DevTools: Move to Userland/DevTools/

Userland/DevTools/HackStudio/AutoCompleteResponse.h

@@ -0,0 +1,67 @@
+/*
+ * Copyright (c) 2020, the SerenityOS developers.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <AK/String.h>
+#include <AK/Types.h>
+#include <LibGUI/AutocompleteProvider.h>
+#include <LibIPC/Decoder.h>
+#include <LibIPC/Encoder.h>
+
+namespace IPC {
+
+template<>
+inline bool encode(IPC::Encoder& encoder, const GUI::AutocompleteProvider::Entry& response)
+{
+    encoder << response.completion;
+    encoder << (u64)response.partial_input_length;
+    encoder << (u32)response.kind;
+    encoder << (u32)response.language;
+    return true;
+}
+
+template<>
+inline bool decode(IPC::Decoder& decoder, GUI::AutocompleteProvider::Entry& response)
+{
+    u32 kind = 0;
+    u32 language = 0;
+    u64 partial_input_length = 0;
+    bool ok = decoder.decode(response.completion)
+        && decoder.decode(partial_input_length)
+        && decoder.decode(kind)
+        && decoder.decode(language);
+
+    if (ok) {
+        response.kind = static_cast<GUI::AutocompleteProvider::CompletionKind>(kind);
+        response.language = static_cast<GUI::AutocompleteProvider::Language>(language);
+        response.partial_input_length = partial_input_length;
+    }
+
+    return ok;
+}
+
+}

Userland/DevTools/HackStudio/CMakeLists.txt

@@ -0,0 +1,37 @@
+add_subdirectory(LanguageServers)
+add_subdirectory(LanguageClients)
+
+set(SOURCES
+    CodeDocument.cpp
+    CursorTool.cpp
+    Debugger/BacktraceModel.cpp
+    Debugger/DebugInfoWidget.cpp
+    Debugger/Debugger.cpp
+    Debugger/DisassemblyModel.cpp
+    Debugger/DisassemblyWidget.cpp
+    Debugger/RegistersModel.cpp
+    Debugger/VariablesModel.cpp
+    Editor.cpp
+    EditorWrapper.cpp
+    FindInFilesWidget.cpp
+    FormEditorWidget.cpp
+    FormWidget.cpp
+    Git/DiffViewer.cpp
+    Git/GitFilesModel.cpp
+    Git/GitFilesView.cpp
+    Git/GitRepo.cpp
+    Git/GitWidget.cpp
+    HackStudioWidget.cpp
+    LanguageClient.cpp
+    Locator.cpp
+    Project.cpp
+    ProjectFile.cpp
+    TerminalWrapper.cpp
+    WidgetTool.cpp
+    WidgetTreeModel.cpp
+    main.cpp
+)
+
+serenity_app(HackStudio ICON app-hack-studio)
+target_link_libraries(HackStudio LibWeb LibMarkdown LibGUI LibGfx LibCore LibVT LibDebug LibX86 LibDiff LibShell)
+add_dependencies(HackStudio CppLanguageServer)

Userland/DevTools/HackStudio/CodeDocument.cpp

@@ -0,0 +1,68 @@
+/*
+ * Copyright (c) 2020, Itamar S. <itamar8910@gmail.com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "CodeDocument.h"
+
+namespace HackStudio {
+
+NonnullRefPtr<CodeDocument> CodeDocument::create(const String& file_path, Client* client)
+{
+    return adopt(*new CodeDocument(file_path, client));
+}
+
+NonnullRefPtr<CodeDocument> CodeDocument::create(Client* client)
+{
+    return adopt(*new CodeDocument(client));
+}
+
+CodeDocument::CodeDocument(const String& file_path, Client* client)
+    : TextDocument(client)
+    , m_file_path(file_path)
+{
+    LexicalPath lexical_path(file_path);
+
+    if (lexical_path.has_extension(".cpp") || lexical_path.has_extension(".h"))
+        m_language = Language::Cpp;
+    else if (lexical_path.has_extension(".js"))
+        m_language = Language::JavaScript;
+    else if (lexical_path.has_extension(".gml"))
+        m_language = Language::GML;
+    else if (lexical_path.has_extension(".ini"))
+        m_language = Language::Ini;
+    else if (lexical_path.has_extension(".sh"))
+        m_language = Language::Shell;
+}
+
+CodeDocument::CodeDocument(Client* client)
+    : TextDocument(client)
+{
+}
+
+CodeDocument::~CodeDocument()
+{
+}
+
+}

Userland/DevTools/HackStudio/CodeDocument.h

@@ -0,0 +1,61 @@
+/*
+ * Copyright (c) 2020, Itamar S. <itamar8910@gmail.com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include "Language.h"
+#include <AK/LexicalPath.h>
+#include <LibGUI/TextDocument.h>
+
+namespace HackStudio {
+
+class CodeDocument final : public GUI::TextDocument {
+public:
+    virtual ~CodeDocument() override;
+    static NonnullRefPtr<CodeDocument> create(const String& file_path, Client* client = nullptr);
+    static NonnullRefPtr<CodeDocument> create(Client* client = nullptr);
+
+    const Vector<size_t>& breakpoint_lines() const { return m_breakpoint_lines; }
+    Vector<size_t>& breakpoint_lines() { return m_breakpoint_lines; }
+    Optional<size_t> execution_position() const { return m_execution_position; }
+    void set_execution_position(size_t line) { m_execution_position = line; }
+    void clear_execution_position() { m_execution_position.clear(); }
+    const String& file_path() const { return m_file_path; }
+    Language language() const { return m_language; }
+
+    virtual bool is_code_document() const override final { return true; }
+
+private:
+    explicit CodeDocument(const String& file_path, Client* client = nullptr);
+    explicit CodeDocument(Client* client = nullptr);
+
+    String m_file_path;
+    Language m_language { Language::Unknown };
+    Vector<size_t> m_breakpoint_lines;
+    Optional<size_t> m_execution_position;
+};
+
+}

Userland/DevTools/HackStudio/CursorTool.cpp

@@ -0,0 +1,204 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "CursorTool.h"
+#include "FormEditorWidget.h"
+#include "FormWidget.h"
+#include "WidgetTreeModel.h"
+#include <AK/LogStream.h>
+#include <LibGfx/Palette.h>
+
+//#define DEBUG_CURSOR_TOOL
+
+namespace HackStudio {
+
+void CursorTool::on_mousedown(GUI::MouseEvent& event)
+{
+#ifdef DEBUG_CURSOR_TOOL
+    dbgln("CursorTool::on_mousedown");
+#endif
+    auto& form_widget = m_editor.form_widget();
+    auto result = form_widget.hit_test(event.position(), GUI::Widget::ShouldRespectGreediness::No);
+
+    if (event.button() == GUI::MouseButton::Left) {
+        if (result.widget && result.widget != &form_widget) {
+            if (event.modifiers() & Mod_Ctrl) {
+                m_editor.selection().toggle(*result.widget);
+            } else if (!event.modifiers()) {
+                if (!m_editor.selection().contains(*result.widget)) {
+#ifdef DEBUG_CURSOR_TOOL
+                    dbg() << "Selection didn't contain " << *result.widget << ", making it the only selected one";
+#endif
+                    m_editor.selection().set(*result.widget);
+                }
+
+                m_drag_origin = event.position();
+                m_positions_before_drag.clear();
+                m_editor.selection().for_each([&](auto& widget) {
+                    m_positions_before_drag.set(&widget, widget.relative_position());
+                    return IterationDecision::Continue;
+                });
+            }
+        } else {
+            m_editor.selection().clear();
+            m_rubber_banding = true;
+            m_rubber_band_origin = event.position();
+            m_rubber_band_position = event.position();
+            form_widget.update();
+        }
+        // FIXME: Do we need to update any part of the FormEditorWidget outside the FormWidget?
+        form_widget.update();
+    }
+}
+
+void CursorTool::on_mouseup(GUI::MouseEvent& event)
+{
+#ifdef DEBUG_CURSOR_TOOL
+    dbgln("CursorTool::on_mouseup");
+#endif
+    if (event.button() == GUI::MouseButton::Left) {
+        auto& form_widget = m_editor.form_widget();
+        auto result = form_widget.hit_test(event.position(), GUI::Widget::ShouldRespectGreediness::No);
+        if (!m_dragging && !(event.modifiers() & Mod_Ctrl)) {
+            if (result.widget && result.widget != &form_widget) {
+                m_editor.selection().set(*result.widget);
+                // FIXME: Do we need to update any part of the FormEditorWidget outside the FormWidget?
+                form_widget.update();
+            }
+        }
+        m_dragging = false;
+        m_rubber_banding = false;
+        form_widget.update();
+    }
+}
+
+void CursorTool::on_mousemove(GUI::MouseEvent& event)
+{
+#ifdef DEBUG_CURSOR_TOOL
+    dbgln("CursorTool::on_mousemove");
+#endif
+    auto& form_widget = m_editor.form_widget();
+
+    if (m_rubber_banding) {
+        set_rubber_band_position(event.position());
+        return;
+    }
+
+    if (!m_dragging && event.buttons() & GUI::MouseButton::Left && event.position() != m_drag_origin) {
+        auto result = form_widget.hit_test(event.position(), GUI::Widget::ShouldRespectGreediness::No);
+        if (result.widget && result.widget != &form_widget) {
+            if (!m_editor.selection().contains(*result.widget)) {
+                m_editor.selection().set(*result.widget);
+                // FIXME: Do we need to update any part of the FormEditorWidget outside the FormWidget?
+                form_widget.update();
+            }
+        }
+        m_dragging = true;
+    }
+
+    if (m_dragging) {
+        auto movement_delta = event.position() - m_drag_origin;
+        m_editor.selection().for_each([&](auto& widget) {
+            auto new_rect = widget.relative_rect();
+            new_rect.set_location(m_positions_before_drag.get(&widget).value_or({}).translated(movement_delta));
+            new_rect.set_x(new_rect.x() - (new_rect.x() % m_editor.form_widget().grid_size()));
+            new_rect.set_y(new_rect.y() - (new_rect.y() % m_editor.form_widget().grid_size()));
+            widget.set_relative_rect(new_rect);
+            return IterationDecision::Continue;
+        });
+        m_editor.model().update();
+        return;
+    }
+}
+
+void CursorTool::on_keydown(GUI::KeyEvent& event)
+{
+#ifdef DEBUG_CURSOR_TOOL
+    dbgln("CursorTool::on_keydown");
+#endif
+
+    auto move_selected_widgets_by = [this](int x, int y) {
+        m_editor.selection().for_each([&](auto& widget) {
+            widget.move_by(x, y);
+            return IterationDecision::Continue;
+        });
+    };
+
+    if (event.modifiers() == 0) {
+        switch (event.key()) {
+        case Key_Down:
+            move_selected_widgets_by(0, m_editor.form_widget().grid_size());
+            break;
+        case Key_Up:
+            move_selected_widgets_by(0, -m_editor.form_widget().grid_size());
+            break;
+        case Key_Left:
+            move_selected_widgets_by(-m_editor.form_widget().grid_size(), 0);
+            break;
+        case Key_Right:
+            move_selected_widgets_by(m_editor.form_widget().grid_size(), 0);
+            break;
+        default:
+            break;
+        }
+    }
+}
+
+void CursorTool::set_rubber_band_position(const Gfx::IntPoint& position)
+{
+    if (m_rubber_band_position == position)
+        return;
+    m_rubber_band_position = position;
+
+    auto rubber_band_rect = this->rubber_band_rect();
+
+    m_editor.selection().clear();
+    m_editor.form_widget().for_each_child_widget([&](auto& child) {
+        if (child.relative_rect().intersects(rubber_band_rect))
+            m_editor.selection().add(child);
+        return IterationDecision::Continue;
+    });
+
+    m_editor.form_widget().update();
+}
+
+Gfx::IntRect CursorTool::rubber_band_rect() const
+{
+    if (!m_rubber_banding)
+        return {};
+    return Gfx::IntRect::from_two_points(m_rubber_band_origin, m_rubber_band_position);
+}
+
+void CursorTool::on_second_paint(GUI::Painter& painter, GUI::PaintEvent&)
+{
+    if (!m_rubber_banding)
+        return;
+    auto rect = rubber_band_rect();
+    painter.fill_rect(rect, m_editor.palette().rubber_band_fill());
+    painter.draw_rect(rect, m_editor.palette().rubber_band_border());
+}
+
+}

Userland/DevTools/HackStudio/CursorTool.h

@@ -0,0 +1,64 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include "Tool.h"
+#include <AK/HashMap.h>
+#include <LibGUI/Forward.h>
+#include <LibGfx/Point.h>
+
+namespace HackStudio {
+
+class CursorTool final : public Tool {
+public:
+    explicit CursorTool(FormEditorWidget& editor)
+        : Tool(editor)
+    {
+    }
+    virtual ~CursorTool() override { }
+
+private:
+    virtual const char* class_name() const override { return "CursorTool"; }
+    virtual void on_mousedown(GUI::MouseEvent&) override;
+    virtual void on_mouseup(GUI::MouseEvent&) override;
+    virtual void on_mousemove(GUI::MouseEvent&) override;
+    virtual void on_keydown(GUI::KeyEvent&) override;
+    virtual void on_second_paint(GUI::Painter&, GUI::PaintEvent&) override;
+
+    void set_rubber_band_position(const Gfx::IntPoint&);
+    Gfx::IntRect rubber_band_rect() const;
+
+    Gfx::IntPoint m_drag_origin;
+    HashMap<GUI::Widget*, Gfx::IntPoint> m_positions_before_drag;
+    bool m_dragging { false };
+
+    bool m_rubber_banding { false };
+    Gfx::IntPoint m_rubber_band_origin;
+    Gfx::IntPoint m_rubber_band_position;
+};
+
+}

Userland/DevTools/HackStudio/Debugger/BacktraceModel.cpp

@@ -0,0 +1,78 @@
+/*
+ * Copyright (c) 2020, Itamar S. <itamar8910@gmail.com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "BacktraceModel.h"
+#include "Debugger.h"
+#include <LibDebug/StackFrameUtils.h>
+
+namespace HackStudio {
+
+NonnullRefPtr<BacktraceModel> BacktraceModel::create(const Debug::DebugSession& debug_session, const PtraceRegisters& regs)
+{
+    return adopt(*new BacktraceModel(create_backtrace(debug_session, regs)));
+}
+
+GUI::Variant BacktraceModel::data(const GUI::ModelIndex& index, GUI::ModelRole role) const
+{
+    if (role == GUI::ModelRole::Display) {
+        auto& frame = m_frames.at(index.row());
+        return frame.function_name;
+    }
+    return {};
+}
+
+GUI::ModelIndex BacktraceModel::index(int row, int column, const GUI::ModelIndex&) const
+{
+    if (row < 0 || row >= static_cast<int>(m_frames.size()))
+        return {};
+    return create_index(row, column, &m_frames.at(row));
+}
+
+Vector<BacktraceModel::FrameInfo> BacktraceModel::create_backtrace(const Debug::DebugSession& debug_session, const PtraceRegisters& regs)
+{
+    u32 current_ebp = regs.ebp;
+    u32 current_instruction = regs.eip;
+    Vector<BacktraceModel::FrameInfo> frames;
+    do {
+        auto lib = debug_session.library_at(regs.eip);
+        if (!lib)
+            continue;
+        String name = lib->debug_info->name_of_containing_function(current_instruction - lib->base_address);
+        if (name.is_null()) {
+            dbgln("BacktraceModel: couldn't find containing function for address: {:p}", current_instruction);
+            name = "<missing>";
+        }
+
+        frames.append({ name, current_instruction, current_ebp });
+        auto frame_info = Debug::StackFrameUtils::get_info(*Debugger::the().session(), current_ebp);
+        ASSERT(frame_info.has_value());
+        current_instruction = frame_info.value().return_address;
+        current_ebp = frame_info.value().next_ebp;
+    } while (current_ebp && current_instruction);
+    return frames;
+}
+
+}

Userland/DevTools/HackStudio/Debugger/BacktraceModel.h

@@ -0,0 +1,78 @@
+/*
+ * Copyright (c) 2020, Itamar S. <itamar8910@gmail.com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <AK/Vector.h>
+#include <LibGUI/ListView.h>
+#include <LibGUI/Model.h>
+#include <sys/arch/i386/regs.h>
+
+namespace Debug {
+
+class DebugSession;
+
+}
+
+namespace HackStudio {
+
+class BacktraceModel final : public GUI::Model {
+public:
+    static NonnullRefPtr<BacktraceModel> create(const Debug::DebugSession&, const PtraceRegisters& regs);
+
+    virtual int row_count(const GUI::ModelIndex& = GUI::ModelIndex()) const override { return m_frames.size(); }
+    virtual int column_count(const GUI::ModelIndex& = GUI::ModelIndex()) const override { return 1; }
+
+    virtual String column_name(int) const override
+    {
+        return "";
+    }
+
+    virtual GUI::Variant data(const GUI::ModelIndex&, GUI::ModelRole) const override;
+
+    virtual void update() override { }
+    virtual GUI::ModelIndex index(int row, int column, const GUI::ModelIndex&) const override;
+
+    struct FrameInfo {
+        String function_name;
+        u32 instruction_address;
+        u32 frame_base;
+    };
+
+    const Vector<FrameInfo>& frames() const { return m_frames; }
+
+private:
+    explicit BacktraceModel(Vector<FrameInfo>&& frames)
+        : m_frames(move(frames))
+    {
+    }
+
+    static Vector<FrameInfo> create_backtrace(const Debug::DebugSession&, const PtraceRegisters&);
+
+    Vector<FrameInfo> m_frames;
+};
+
+}

Userland/DevTools/HackStudio/Debugger/BreakpointCallback.h

@@ -0,0 +1,42 @@
+/*
+ * Copyright (c) 2020, Itamar S. <itamar8910@gmail.com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <AK/Function.h>
+#include <AK/String.h>
+#include <AK/Types.h>
+
+namespace HackStudio {
+
+enum class BreakpointChange {
+    Added,
+    Removed,
+};
+
+typedef Function<void(const String& file, size_t line, BreakpointChange)> BreakpointChangeCallback;
+
+}

Userland/DevTools/HackStudio/Debugger/DebugInfoWidget.cpp

@@ -0,0 +1,188 @@
+/*
+ * Copyright (c) 2020, Itamar S. <itamar8910@gmail.com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "DebugInfoWidget.h"
+#include "BacktraceModel.h"
+#include "Debugger.h"
+#include "RegistersModel.h"
+#include "VariablesModel.h"
+#include <AK/StringBuilder.h>
+#include <LibGUI/Action.h>
+#include <LibGUI/BoxLayout.h>
+#include <LibGUI/InputBox.h>
+#include <LibGUI/Layout.h>
+#include <LibGUI/ListView.h>
+#include <LibGUI/Menu.h>
+#include <LibGUI/Model.h>
+#include <LibGUI/Splitter.h>
+#include <LibGUI/TabWidget.h>
+#include <LibGUI/TreeView.h>
+
+namespace HackStudio {
+
+void DebugInfoWidget::init_toolbar()
+{
+    m_continue_action = GUI::Action::create("Continue", Gfx::Bitmap::load_from_file("/res/icons/16x16/debug-continue.png"), [](auto&) {
+        Debugger::the().set_requested_debugger_action(Debugger::DebuggerAction::Continue);
+    });
+
+    m_singlestep_action = GUI::Action::create("Step Over", { Mod_None, Key_F10 }, Gfx::Bitmap::load_from_file("/res/icons/16x16/debug-step-over.png"), [](auto&) {
+        Debugger::the().set_requested_debugger_action(Debugger::DebuggerAction::SourceStepOver);
+    });
+
+    m_step_in_action = GUI::Action::create("Step In", { Mod_None, Key_F11 }, Gfx::Bitmap::load_from_file("/res/icons/16x16/debug-step-in.png"), [](auto&) {
+        Debugger::the().set_requested_debugger_action(Debugger::DebuggerAction::SourceSingleStep);
+    });
+
+    m_step_out_action = GUI::Action::create("Step Out", { Mod_Shift, Key_F11 }, Gfx::Bitmap::load_from_file("/res/icons/16x16/debug-step-out.png"), [](auto&) {
+        Debugger::the().set_requested_debugger_action(Debugger::DebuggerAction::SourceStepOut);
+    });
+
+    m_toolbar->add_action(*m_continue_action);
+    m_toolbar->add_action(*m_singlestep_action);
+    m_toolbar->add_action(*m_step_in_action);
+    m_toolbar->add_action(*m_step_out_action);
+
+    set_debug_actions_enabled(false);
+}
+
+DebugInfoWidget::DebugInfoWidget()
+{
+    set_layout<GUI::VerticalBoxLayout>();
+    auto& toolbar_container = add<GUI::ToolBarContainer>();
+    m_toolbar = toolbar_container.add<GUI::ToolBar>();
+    init_toolbar();
+    auto& bottom_box = add<GUI::Widget>();
+    bottom_box.set_layout<GUI::HorizontalBoxLayout>();
+
+    auto& splitter = bottom_box.add<GUI::HorizontalSplitter>();
+    m_backtrace_view = splitter.add<GUI::ListView>();
+    auto& variables_tab_widget = splitter.add<GUI::TabWidget>();
+    variables_tab_widget.set_tab_position(GUI::TabWidget::TabPosition::Bottom);
+    variables_tab_widget.add_widget("Variables", build_variables_tab());
+    variables_tab_widget.add_widget("Registers", build_registers_tab());
+
+    m_backtrace_view->on_selection = [this](auto& index) {
+        auto& model = static_cast<BacktraceModel&>(*m_backtrace_view->model());
+
+        // Note: The reconstruction of the register set here is obviously incomplete.
+        // We currently only reconstruct eip & ebp. Ideally would also reconstruct the other registers somehow.
+        // (Other registers may be needed to get the values of variables who are not stored on the stack)
+        PtraceRegisters frame_regs {};
+        frame_regs.eip = model.frames()[index.row()].instruction_address;
+        frame_regs.ebp = model.frames()[index.row()].frame_base;
+
+        m_variables_view->set_model(VariablesModel::create(frame_regs));
+    };
+}
+
+NonnullRefPtr<GUI::Widget> DebugInfoWidget::build_variables_tab()
+{
+    auto variables_widget = GUI::Widget::construct();
+    variables_widget->set_layout<GUI::HorizontalBoxLayout>();
+
+    m_variables_view = variables_widget->add<GUI::TreeView>();
+
+    auto is_valid_index = [](auto& index) {
+        if (!index.is_valid())
+            return false;
+        auto* variable = static_cast<const Debug::DebugInfo::VariableInfo*>(index.internal_data());
+        if (variable->location_type != Debug::DebugInfo::VariableInfo::LocationType::Address)
+            return false;
+        return variable->is_enum_type() || variable->type_name.is_one_of("int", "bool");
+    };
+
+    m_variables_view->on_context_menu_request = [this, is_valid_index](auto& index, auto& event) {
+        if (!is_valid_index(index))
+            return;
+        m_variable_context_menu->popup(event.screen_position());
+    };
+
+    m_variables_view->on_activation = [this, is_valid_index](auto& index) {
+        if (!is_valid_index(index))
+            return;
+
+        String value;
+        if (GUI::InputBox::show(value, window(), "Enter new value:", "Set variable value") == GUI::InputBox::ExecOK) {
+            auto& model = static_cast<VariablesModel&>(*m_variables_view->model());
+            model.set_variable_value(index, value, window());
+        }
+    };
+
+    auto edit_variable_action = GUI::Action::create("Change value", [this](auto&) {
+        m_variables_view->on_activation(m_variables_view->selection().first());
+    });
+
+    m_variable_context_menu = GUI::Menu::construct();
+    m_variable_context_menu->add_action(edit_variable_action);
+
+    return variables_widget;
+}
+
+NonnullRefPtr<GUI::Widget> DebugInfoWidget::build_registers_tab()
+{
+    auto registers_widget = GUI::Widget::construct();
+    registers_widget->set_layout<GUI::HorizontalBoxLayout>();
+
+    m_registers_view = registers_widget->add<GUI::TableView>();
+
+    return registers_widget;
+}
+
+void DebugInfoWidget::update_state(const Debug::DebugSession& debug_session, const PtraceRegisters& regs)
+{
+    m_variables_view->set_model(VariablesModel::create(regs));
+    m_backtrace_view->set_model(BacktraceModel::create(debug_session, regs));
+    if (m_registers_view->model()) {
+        auto& previous_registers = static_cast<RegistersModel*>(m_registers_view->model())->raw_registers();
+        m_registers_view->set_model(RegistersModel::create(regs, previous_registers));
+    } else {
+        m_registers_view->set_model(RegistersModel::create(regs));
+    }
+    auto selected_index = m_backtrace_view->model()->index(0);
+    if (!selected_index.is_valid()) {
+        dbgln("Warning: DebugInfoWidget: backtrace selected index is invalid");
+        return;
+    }
+    m_backtrace_view->selection().set(selected_index);
+}
+
+void DebugInfoWidget::program_stopped()
+{
+    m_variables_view->set_model({});
+    m_backtrace_view->set_model({});
+    m_registers_view->set_model({});
+}
+
+void DebugInfoWidget::set_debug_actions_enabled(bool enabled)
+{
+    m_continue_action->set_enabled(enabled);
+    m_singlestep_action->set_enabled(enabled);
+    m_step_in_action->set_enabled(enabled);
+    m_step_out_action->set_enabled(enabled);
+}
+
+}

Userland/DevTools/HackStudio/Debugger/DebugInfoWidget.h

@@ -0,0 +1,71 @@
+/*
+ * Copyright (c) 2020, Itamar S. <itamar8910@gmail.com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include "Debugger.h"
+#include <AK/NonnullOwnPtr.h>
+#include <LibGUI/Action.h>
+#include <LibGUI/ListView.h>
+#include <LibGUI/Menu.h>
+#include <LibGUI/Model.h>
+#include <LibGUI/TableView.h>
+#include <LibGUI/ToolBar.h>
+#include <LibGUI/ToolBarContainer.h>
+#include <LibGUI/TreeView.h>
+#include <LibGUI/Widget.h>
+#include <sys/arch/i386/regs.h>
+
+namespace HackStudio {
+
+class DebugInfoWidget final : public GUI::Widget {
+    C_OBJECT(DebugInfoWidget)
+public:
+    virtual ~DebugInfoWidget() override { }
+
+    void update_state(const Debug::DebugSession&, const PtraceRegisters&);
+    void program_stopped();
+    void set_debug_actions_enabled(bool enabled);
+
+private:
+    explicit DebugInfoWidget();
+    void init_toolbar();
+
+    NonnullRefPtr<GUI::Widget> build_variables_tab();
+    NonnullRefPtr<GUI::Widget> build_registers_tab();
+
+    RefPtr<GUI::TreeView> m_variables_view;
+    RefPtr<GUI::TableView> m_registers_view;
+    RefPtr<GUI::ListView> m_backtrace_view;
+    RefPtr<GUI::Menu> m_variable_context_menu;
+    RefPtr<GUI::ToolBar> m_toolbar;
+    RefPtr<GUI::Action> m_continue_action;
+    RefPtr<GUI::Action> m_singlestep_action;
+    RefPtr<GUI::Action> m_step_in_action;
+    RefPtr<GUI::Action> m_step_out_action;
+};
+
+}

Userland/DevTools/HackStudio/Debugger/Debugger.cpp

@@ -0,0 +1,295 @@
+/*
+ * Copyright (c) 2020, Itamar S. <itamar8910@gmail.com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "Debugger.h"
+#include <LibDebug/StackFrameUtils.h>
+
+namespace HackStudio {
+
+static Debugger* s_the;
+
+Debugger& Debugger::the()
+{
+    ASSERT(s_the);
+    return *s_the;
+}
+
+void Debugger::initialize(
+    String source_root,
+    Function<HasControlPassedToUser(const PtraceRegisters&)> on_stop_callback,
+    Function<void()> on_continue_callback,
+    Function<void()> on_exit_callback)
+{
+    s_the = new Debugger(source_root, move(on_stop_callback), move(on_continue_callback), move(on_exit_callback));
+}
+
+bool Debugger::is_initialized()
+{
+    return s_the;
+}
+
+Debugger::Debugger(
+    String source_root,
+    Function<HasControlPassedToUser(const PtraceRegisters&)> on_stop_callback,
+    Function<void()> on_continue_callback,
+    Function<void()> on_exit_callback)
+    : m_source_root(source_root)
+    , m_on_stopped_callback(move(on_stop_callback))
+    , m_on_continue_callback(move(on_continue_callback))
+    , m_on_exit_callback(move(on_exit_callback))
+{
+    pthread_mutex_init(&m_ui_action_mutex, nullptr);
+    pthread_cond_init(&m_ui_action_cond, nullptr);
+}
+
+void Debugger::on_breakpoint_change(const String& file, size_t line, BreakpointChange change_type)
+{
+    auto position = create_source_position(file, line);
+
+    if (change_type == BreakpointChange::Added) {
+        Debugger::the().m_breakpoints.append(position);
+    } else {
+        Debugger::the().m_breakpoints.remove_all_matching([&](Debug::DebugInfo::SourcePosition val) { return val == position; });
+    }
+
+    auto session = Debugger::the().session();
+    if (!session)
+        return;
+
+    auto address = session->get_address_from_source_position(position.file_path, position.line_number);
+    if (!address.has_value()) {
+        dbgln("Warning: couldn't get instruction address from source");
+        // TODO: Currently, the GUI will indicate that a breakpoint was inserted/removed at this line,
+        // regardless of whether we actually succeeded to insert it. (For example a breakpoint on a comment, or an include statement).
+        // We should indicate failure via a return value from this function, and not update the breakpoint GUI if we fail.
+        return;
+    }
+
+    if (change_type == BreakpointChange::Added) {
+        bool success = session->insert_breakpoint(reinterpret_cast<void*>(address.value().address));
+        ASSERT(success);
+    } else {
+        bool success = session->remove_breakpoint(reinterpret_cast<void*>(address.value().address));
+        ASSERT(success);
+    }
+}
+
+Debug::DebugInfo::SourcePosition Debugger::create_source_position(const String& file, size_t line)
+{
+    if (!file.starts_with('/') && !file.starts_with("./"))
+        return { String::formatted("./{}", file), line + 1 };
+    return { file, line + 1 };
+}
+
+int Debugger::start_static()
+{
+    Debugger::the().start();
+    return 0;
+}
+
+void Debugger::start()
+{
+    m_debug_session = Debug::DebugSession::exec_and_attach(m_executable_path, m_source_root);
+    ASSERT(!!m_debug_session);
+
+    for (const auto& breakpoint : m_breakpoints) {
+        dbgln("inserting breakpoint at: {}:{}", breakpoint.file_path, breakpoint.line_number);
+        auto address = m_debug_session->get_address_from_source_position(breakpoint.file_path, breakpoint.line_number);
+        if (address.has_value()) {
+            bool success = m_debug_session->insert_breakpoint(reinterpret_cast<void*>(address.value().address));
+            ASSERT(success);
+        } else {
+            dbgln("couldn't insert breakpoint");
+        }
+    }
+
+    debugger_loop();
+}
+
+int Debugger::debugger_loop()
+{
+    ASSERT(m_debug_session);
+
+    m_debug_session->run(Debug::DebugSession::DesiredInitialDebugeeState::Running, [this](Debug::DebugSession::DebugBreakReason reason, Optional<PtraceRegisters> optional_regs) {
+        if (reason == Debug::DebugSession::DebugBreakReason::Exited) {
+            dbgln("Program exited");
+            m_on_exit_callback();
+            return Debug::DebugSession::DebugDecision::Detach;
+        }
+        remove_temporary_breakpoints();
+        ASSERT(optional_regs.has_value());
+        const PtraceRegisters& regs = optional_regs.value();
+
+        auto source_position = m_debug_session->get_source_position(regs.eip);
+        if (!source_position.has_value())
+            return Debug::DebugSession::DebugDecision::SingleStep;
+
+        // We currently do no support stepping through assembly source
+        if (source_position.value().file_path.ends_with(".S"))
+            return Debug::DebugSession::DebugDecision::SingleStep;
+
+        ASSERT(source_position.has_value());
+        if (m_state.get() == Debugger::DebuggingState::SingleStepping) {
+            if (m_state.should_stop_single_stepping(source_position.value())) {
+                m_state.set_normal();
+            } else {
+                return Debug::DebugSession::DebugDecision::SingleStep;
+            }
+        }
+
+        auto control_passed_to_user = m_on_stopped_callback(regs);
+
+        if (control_passed_to_user == HasControlPassedToUser::Yes) {
+            pthread_mutex_lock(&m_ui_action_mutex);
+            pthread_cond_wait(&m_ui_action_cond, &m_ui_action_mutex);
+            pthread_mutex_unlock(&m_ui_action_mutex);
+
+            if (m_requested_debugger_action != DebuggerAction::Exit)
+                m_on_continue_callback();
+
+        } else {
+            m_requested_debugger_action = DebuggerAction::Continue;
+        }
+
+        switch (m_requested_debugger_action) {
+        case DebuggerAction::Continue:
+            m_state.set_normal();
+            return Debug::DebugSession::DebugDecision::Continue;
+        case DebuggerAction::SourceSingleStep:
+            m_state.set_single_stepping(source_position.value());
+            return Debug::DebugSession::DebugDecision::SingleStep;
+        case DebuggerAction::SourceStepOut:
+            m_state.set_stepping_out();
+            do_step_out(regs);
+            return Debug::DebugSession::DebugDecision::Continue;
+        case DebuggerAction::SourceStepOver:
+            m_state.set_stepping_over();
+            do_step_over(regs);
+            return Debug::DebugSession::DebugDecision::Continue;
+        case DebuggerAction::Exit:
+            // NOTE: Is detaching from the debuggee the best thing to do here?
+            // We could display a dialog in the UI, remind the user that there is
+            // a live debugged process, and ask whether they want to terminate/detach.
+            dbgln("Debugger exiting");
+            return Debug::DebugSession::DebugDecision::Detach;
+        }
+        ASSERT_NOT_REACHED();
+    });
+    m_debug_session.clear();
+    return 0;
+}
+
+void Debugger::DebuggingState::set_normal()
+{
+    m_state = State::Normal;
+    m_original_source_position.clear();
+}
+
+void Debugger::DebuggingState::set_single_stepping(Debug::DebugInfo::SourcePosition original_source_position)
+{
+    m_state = State::SingleStepping;
+    m_original_source_position = original_source_position;
+}
+
+bool Debugger::DebuggingState::should_stop_single_stepping(const Debug::DebugInfo::SourcePosition& current_source_position) const
+{
+    ASSERT(m_state == State::SingleStepping);
+    return m_original_source_position.value() != current_source_position;
+}
+
+void Debugger::remove_temporary_breakpoints()
+{
+    for (auto breakpoint_address : m_state.temporary_breakpoints()) {
+        ASSERT(m_debug_session->breakpoint_exists((void*)breakpoint_address));
+        bool rc = m_debug_session->remove_breakpoint((void*)breakpoint_address);
+        ASSERT(rc);
+    }
+    m_state.clear_temporary_breakpoints();
+}
+
+void Debugger::DebuggingState::clear_temporary_breakpoints()
+{
+    m_addresses_of_temporary_breakpoints.clear();
+}
+void Debugger::DebuggingState::add_temporary_breakpoint(u32 address)
+{
+    m_addresses_of_temporary_breakpoints.append(address);
+}
+
+void Debugger::do_step_out(const PtraceRegisters& regs)
+{
+    // To step out, we simply insert a temporary breakpoint at the
+    // instruction the current function returns to, and continue
+    // execution until we hit that instruction (or some other breakpoint).
+    insert_temporary_breakpoint_at_return_address(regs);
+}
+
+void Debugger::do_step_over(const PtraceRegisters& regs)
+{
+    // To step over, we insert a temporary breakpoint at each line in the current function,
+    // as well as at the current function's return point, and continue execution.
+    auto lib = m_debug_session->library_at(regs.eip);
+    if (!lib)
+        return;
+    auto current_function = lib->debug_info->get_containing_function(regs.eip - lib->base_address);
+    if (!current_function.has_value()) {
+        dbgln("cannot perform step_over, failed to find containing function of: {:p}", regs.eip);
+        return;
+    }
+    ASSERT(current_function.has_value());
+    auto lines_in_current_function = lib->debug_info->source_lines_in_scope(current_function.value());
+    for (const auto& line : lines_in_current_function) {
+        insert_temporary_breakpoint(line.address_of_first_statement.value() + lib->base_address);
+    }
+    insert_temporary_breakpoint_at_return_address(regs);
+}
+
+void Debugger::insert_temporary_breakpoint_at_return_address(const PtraceRegisters& regs)
+{
+    auto frame_info = Debug::StackFrameUtils::get_info(*m_debug_session, regs.ebp);
+    ASSERT(frame_info.has_value());
+    u32 return_address = frame_info.value().return_address;
+    insert_temporary_breakpoint(return_address);
+}
+
+void Debugger::insert_temporary_breakpoint(FlatPtr address)
+{
+    if (m_debug_session->breakpoint_exists((void*)address))
+        return;
+    bool success = m_debug_session->insert_breakpoint(reinterpret_cast<void*>(address));
+    ASSERT(success);
+    m_state.add_temporary_breakpoint(address);
+}
+
+void Debugger::set_requested_debugger_action(DebuggerAction action)
+{
+    pthread_mutex_lock(continue_mutex());
+    m_requested_debugger_action = action;
+    pthread_cond_signal(continue_cond());
+    pthread_mutex_unlock(continue_mutex());
+}
+
+}

Userland/DevTools/HackStudio/Debugger/Debugger.h

@@ -0,0 +1,139 @@
+/*
+ * Copyright (c) 2020, Itamar S. <itamar8910@gmail.com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include "BreakpointCallback.h"
+#include <AK/Function.h>
+#include <AK/Vector.h>
+#include <LibDebug/DebugSession.h>
+#include <LibThread/Lock.h>
+#include <LibThread/Thread.h>
+
+namespace HackStudio {
+
+class Debugger {
+public:
+    static Debugger& the();
+
+    enum class HasControlPassedToUser {
+        No,
+        Yes,
+    };
+
+    static void initialize(
+        String source_root,
+        Function<HasControlPassedToUser(const PtraceRegisters&)> on_stop_callback,
+        Function<void()> on_continue_callback,
+        Function<void()> on_exit_callback);
+
+    static bool is_initialized();
+
+    static void on_breakpoint_change(const String& file, size_t line, BreakpointChange change_type);
+
+    void set_executable_path(const String& path) { m_executable_path = path; }
+
+    Debug::DebugSession* session() { return m_debug_session.ptr(); }
+
+    // Thread entry point
+    static int start_static();
+
+    pthread_mutex_t* continue_mutex() { return &m_ui_action_mutex; }
+    pthread_cond_t* continue_cond() { return &m_ui_action_cond; }
+
+    enum class DebuggerAction {
+        Continue,
+        SourceSingleStep,
+        SourceStepOut,
+        SourceStepOver,
+        Exit,
+    };
+
+    void set_requested_debugger_action(DebuggerAction);
+    void reset_breakpoints() { m_breakpoints.clear(); }
+
+private:
+    class DebuggingState {
+    public:
+        enum State {
+            Normal, // Continue normally until we hit a breakpoint / program terminates
+            SingleStepping,
+            SteppingOut,
+            SteppingOver,
+        };
+        State get() const { return m_state; }
+
+        void set_normal();
+        void set_single_stepping(Debug::DebugInfo::SourcePosition original_source_position);
+        void set_stepping_out() { m_state = State::SteppingOut; }
+        void set_stepping_over() { m_state = State::SteppingOver; }
+
+        bool should_stop_single_stepping(const Debug::DebugInfo::SourcePosition& current_source_position) const;
+        void clear_temporary_breakpoints();
+        void add_temporary_breakpoint(u32 address);
+        const Vector<u32>& temporary_breakpoints() const { return m_addresses_of_temporary_breakpoints; }
+
+    private:
+        State m_state { Normal };
+        Optional<Debug::DebugInfo::SourcePosition> m_original_source_position; // The source position at which we started the current single step
+        Vector<u32> m_addresses_of_temporary_breakpoints;
+    };
+
+    explicit Debugger(
+        String source_root,
+        Function<HasControlPassedToUser(const PtraceRegisters&)> on_stop_callback,
+        Function<void()> on_continue_callback,
+        Function<void()> on_exit_callback);
+
+    static Debug::DebugInfo::SourcePosition create_source_position(const String& file, size_t line);
+
+    void start();
+    int debugger_loop();
+
+    void remove_temporary_breakpoints();
+    void do_step_out(const PtraceRegisters&);
+    void do_step_over(const PtraceRegisters&);
+    void insert_temporary_breakpoint(FlatPtr address);
+    void insert_temporary_breakpoint_at_return_address(const PtraceRegisters&);
+
+    OwnPtr<Debug::DebugSession> m_debug_session;
+    String m_source_root;
+    DebuggingState m_state;
+
+    pthread_mutex_t m_ui_action_mutex {};
+    pthread_cond_t m_ui_action_cond {};
+    DebuggerAction m_requested_debugger_action { DebuggerAction::Continue };
+
+    Vector<Debug::DebugInfo::SourcePosition> m_breakpoints;
+
+    String m_executable_path;
+
+    Function<HasControlPassedToUser(const PtraceRegisters&)> m_on_stopped_callback;
+    Function<void()> m_on_continue_callback;
+    Function<void()> m_on_exit_callback;
+};
+
+}

Userland/DevTools/HackStudio/Debugger/DisassemblyModel.cpp

@@ -0,0 +1,137 @@
+/*
+ * Copyright (c) 2020, Luke Wilde <luke.wilde@live.co.uk>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "DisassemblyModel.h"
+#include <AK/MappedFile.h>
+#include <AK/StringBuilder.h>
+#include <LibDebug/DebugSession.h>
+#include <LibELF/Image.h>
+#include <LibX86/Disassembler.h>
+#include <LibX86/ELFSymbolProvider.h>
+#include <ctype.h>
+#include <stdio.h>
+
+namespace HackStudio {
+
+DisassemblyModel::DisassemblyModel(const Debug::DebugSession& debug_session, const PtraceRegisters& regs)
+{
+    auto lib = debug_session.library_at(regs.eip);
+    if (!lib)
+        return;
+    auto containing_function = lib->debug_info->get_containing_function(regs.eip - lib->base_address);
+    if (!containing_function.has_value()) {
+        dbgln("Cannot disassemble as the containing function was not found.");
+        return;
+    }
+
+    OwnPtr<ELF::Image> kernel_elf;
+    const ELF::Image* elf = nullptr;
+
+    if (containing_function.value().address_low >= 0xc0000000) {
+        auto file_or_error = MappedFile::map("/boot/Kernel");
+        if (file_or_error.is_error())
+            return;
+        kernel_elf = make<ELF::Image>(file_or_error.value()->bytes());
+        elf = kernel_elf.ptr();
+    } else {
+        elf = &lib->debug_info->elf();
+    }
+
+    auto symbol = elf->find_symbol(containing_function.value().address_low);
+    if (!symbol.has_value())
+        return;
+    ASSERT(symbol.has_value());
+
+    auto view = symbol.value().raw_data();
+
+    X86::ELFSymbolProvider symbol_provider(*elf);
+    X86::SimpleInstructionStream stream((const u8*)view.characters_without_null_termination(), view.length());
+    X86::Disassembler disassembler(stream);
+
+    size_t offset_into_symbol = 0;
+    for (;;) {
+        auto insn = disassembler.next();
+        if (!insn.has_value())
+            break;
+        FlatPtr address_in_profiled_program = symbol.value().value() + offset_into_symbol;
+        auto disassembly = insn.value().to_string(address_in_profiled_program, &symbol_provider);
+        StringView instruction_bytes = view.substring_view(offset_into_symbol, insn.value().length());
+        m_instructions.append({ insn.value(), disassembly, instruction_bytes, address_in_profiled_program });
+
+        offset_into_symbol += insn.value().length();
+    }
+}
+
+DisassemblyModel::~DisassemblyModel()
+{
+}
+
+int DisassemblyModel::row_count(const GUI::ModelIndex&) const
+{
+    return m_instructions.size();
+}
+
+String DisassemblyModel::column_name(int column) const
+{
+    switch (column) {
+    case Column::Address:
+        return "Address";
+    case Column::InstructionBytes:
+        return "Insn Bytes";
+    case Column::Disassembly:
+        return "Disassembly";
+    default:
+        ASSERT_NOT_REACHED();
+        return {};
+    }
+}
+
+GUI::Variant DisassemblyModel::data(const GUI::ModelIndex& index, GUI::ModelRole role) const
+{
+    auto& insn = m_instructions[index.row()];
+
+    if (role == GUI::ModelRole::Display) {
+        if (index.column() == Column::Address)
+            return String::formatted("{:p}", insn.address);
+        if (index.column() == Column::InstructionBytes) {
+            StringBuilder builder;
+            for (auto ch : insn.bytes)
+                builder.appendff("{:02x} ", static_cast<unsigned char>(ch));
+            return builder.to_string();
+        }
+        if (index.column() == Column::Disassembly)
+            return insn.disassembly;
+        return {};
+    }
+    return {};
+}
+
+void DisassemblyModel::update()
+{
+    did_update();
+}
+
+}

Userland/DevTools/HackStudio/Debugger/DisassemblyModel.h

@@ -0,0 +1,77 @@
+/*
+ * Copyright (c) 2020, Luke Wilde <luke.wilde@live.co.uk>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <AK/Vector.h>
+#include <LibGUI/Model.h>
+#include <LibX86/Instruction.h>
+#include <sys/arch/i386/regs.h>
+
+namespace Debug {
+
+class DebugSession;
+
+}
+
+namespace HackStudio {
+
+struct InstructionData {
+    X86::Instruction insn;
+    String disassembly;
+    StringView bytes;
+    FlatPtr address { 0 };
+};
+
+class DisassemblyModel final : public GUI::Model {
+public:
+    static NonnullRefPtr<DisassemblyModel> create(const Debug::DebugSession& debug_session, const PtraceRegisters& regs)
+    {
+        return adopt(*new DisassemblyModel(debug_session, regs));
+    }
+
+    enum Column {
+        Address,
+        InstructionBytes,
+        Disassembly,
+        __Count
+    };
+
+    virtual ~DisassemblyModel() override;
+
+    virtual int row_count(const GUI::ModelIndex& = GUI::ModelIndex()) const override;
+    virtual int column_count(const GUI::ModelIndex& = GUI::ModelIndex()) const override { return Column::__Count; }
+    virtual String column_name(int) const override;
+    virtual GUI::Variant data(const GUI::ModelIndex&, GUI::ModelRole) const override;
+    virtual void update() override;
+
+private:
+    DisassemblyModel(const Debug::DebugSession&, const PtraceRegisters&);
+
+    Vector<InstructionData> m_instructions;
+};
+
+}

Userland/DevTools/HackStudio/Debugger/DisassemblyWidget.cpp

@@ -0,0 +1,105 @@
+/*
+ * Copyright (c) 2020, Luke Wilde <luke.wilde@live.co.uk>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "DisassemblyWidget.h"
+#include "DisassemblyModel.h"
+#include <LibGUI/BoxLayout.h>
+#include <LibGUI/Painter.h>
+#include <LibGfx/Palette.h>
+
+namespace HackStudio {
+
+void UnavailableDisassemblyWidget::paint_event(GUI::PaintEvent& event)
+{
+    Frame::paint_event(event);
+    if (reason().is_empty())
+        return;
+    GUI::Painter painter(*this);
+    painter.add_clip_rect(event.rect());
+    painter.draw_text(frame_inner_rect(), reason(), Gfx::TextAlignment::Center, palette().window_text(), Gfx::TextElision::Right);
+}
+
+DisassemblyWidget::DisassemblyWidget()
+{
+    set_layout<GUI::VerticalBoxLayout>();
+
+    m_top_container = add<GUI::Widget>();
+    m_top_container->set_layout<GUI::HorizontalBoxLayout>();
+    m_top_container->set_fixed_height(20);
+
+    m_function_name_label = m_top_container->add<GUI::Label>("");
+
+    m_disassembly_view = add<GUI::TableView>();
+
+    m_unavailable_disassembly_widget = add<UnavailableDisassemblyWidget>("");
+
+    hide_disassembly("Program isn't running");
+}
+
+void DisassemblyWidget::update_state(const Debug::DebugSession& debug_session, const PtraceRegisters& regs)
+{
+    m_disassembly_view->set_model(DisassemblyModel::create(debug_session, regs));
+
+    if (m_disassembly_view->model()->row_count() > 0) {
+        auto lib = debug_session.library_at(regs.eip);
+        if (!lib)
+            return;
+        auto containing_function = lib->debug_info->get_containing_function(regs.eip - lib->base_address);
+        if (containing_function.has_value())
+            m_function_name_label->set_text(containing_function.value().name);
+        else
+            m_function_name_label->set_text("<missing>");
+        show_disassembly();
+    } else {
+        hide_disassembly("No disassembly to show for this function");
+    }
+}
+
+void DisassemblyWidget::program_stopped()
+{
+    m_disassembly_view->set_model({});
+    m_function_name_label->set_text("");
+    hide_disassembly("Program isn't running");
+}
+
+void DisassemblyWidget::show_disassembly()
+{
+    m_top_container->set_visible(true);
+    m_disassembly_view->set_visible(true);
+    m_function_name_label->set_visible(true);
+    m_unavailable_disassembly_widget->set_visible(false);
+}
+
+void DisassemblyWidget::hide_disassembly(const String& reason)
+{
+    m_top_container->set_visible(false);
+    m_disassembly_view->set_visible(false);
+    m_function_name_label->set_visible(false);
+    m_unavailable_disassembly_widget->set_visible(true);
+    m_unavailable_disassembly_widget->set_reason(reason);
+}
+
+}

Userland/DevTools/HackStudio/Debugger/DisassemblyWidget.h

@@ -0,0 +1,78 @@
+/*
+ * Copyright (c) 2020, Luke Wilde <luke.wilde@live.co.uk>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include "Debugger.h"
+#include <AK/NonnullOwnPtr.h>
+#include <LibGUI/Label.h>
+#include <LibGUI/Model.h>
+#include <LibGUI/TableView.h>
+#include <LibGUI/Widget.h>
+#include <sys/arch/i386/regs.h>
+
+namespace HackStudio {
+
+class UnavailableDisassemblyWidget final : public GUI::Frame {
+    C_OBJECT(UnavailableDisassemblyWidget)
+public:
+    virtual ~UnavailableDisassemblyWidget() override { }
+
+    const String& reason() const { return m_reason; }
+    void set_reason(const String& text) { m_reason = text; }
+
+private:
+    UnavailableDisassemblyWidget(const String& reason)
+        : m_reason(reason)
+    {
+    }
+
+    virtual void paint_event(GUI::PaintEvent& event) override;
+
+    String m_reason;
+};
+
+class DisassemblyWidget final : public GUI::Widget {
+    C_OBJECT(DisassemblyWidget)
+public:
+    virtual ~DisassemblyWidget() override { }
+
+    void update_state(const Debug::DebugSession&, const PtraceRegisters&);
+    void program_stopped();
+
+private:
+    DisassemblyWidget();
+
+    void show_disassembly();
+    void hide_disassembly(const String&);
+
+    RefPtr<GUI::Widget> m_top_container;
+    RefPtr<GUI::TableView> m_disassembly_view;
+    RefPtr<GUI::Label> m_function_name_label;
+    RefPtr<UnavailableDisassemblyWidget> m_unavailable_disassembly_widget;
+};
+
+}

Userland/DevTools/HackStudio/Debugger/RegistersModel.cpp

@@ -0,0 +1,121 @@
+/*
+ * Copyright (c) 2020, Luke Wilde <luke.wilde@live.co.uk>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "RegistersModel.h"
+
+namespace HackStudio {
+
+RegistersModel::RegistersModel(const PtraceRegisters& regs)
+    : m_raw_registers(regs)
+{
+    m_registers.append({ "eax", regs.eax });
+    m_registers.append({ "ebx", regs.ebx });
+    m_registers.append({ "ecx", regs.ecx });
+    m_registers.append({ "edx", regs.edx });
+    m_registers.append({ "esp", regs.esp });
+    m_registers.append({ "ebp", regs.ebp });
+    m_registers.append({ "esi", regs.esi });
+    m_registers.append({ "edi", regs.edi });
+    m_registers.append({ "eip", regs.eip });
+    m_registers.append({ "eflags", regs.eflags });
+    m_registers.append({ "cs", regs.cs });
+    m_registers.append({ "ss", regs.ss });
+    m_registers.append({ "ds", regs.ds });
+    m_registers.append({ "es", regs.es });
+    m_registers.append({ "fs", regs.fs });
+    m_registers.append({ "gs", regs.gs });
+}
+
+RegistersModel::RegistersModel(const PtraceRegisters& current_regs, const PtraceRegisters& previous_regs)
+    : m_raw_registers(current_regs)
+{
+    m_registers.append({ "eax", current_regs.eax, current_regs.eax != previous_regs.eax });
+    m_registers.append({ "ebx", current_regs.ebx, current_regs.ebx != previous_regs.ebx });
+    m_registers.append({ "ecx", current_regs.ecx, current_regs.ecx != previous_regs.ecx });
+    m_registers.append({ "edx", current_regs.edx, current_regs.edx != previous_regs.edx });
+    m_registers.append({ "esp", current_regs.esp, current_regs.esp != previous_regs.esp });
+    m_registers.append({ "ebp", current_regs.ebp, current_regs.ebp != previous_regs.ebp });
+    m_registers.append({ "esi", current_regs.esi, current_regs.esi != previous_regs.esi });
+    m_registers.append({ "edi", current_regs.edi, current_regs.edi != previous_regs.edi });
+    m_registers.append({ "eip", current_regs.eip, current_regs.eip != previous_regs.eip });
+    m_registers.append({ "eflags", current_regs.eflags, current_regs.eflags != previous_regs.eflags });
+    m_registers.append({ "cs", current_regs.cs, current_regs.cs != previous_regs.cs });
+    m_registers.append({ "ss", current_regs.ss, current_regs.ss != previous_regs.ss });
+    m_registers.append({ "ds", current_regs.ds, current_regs.ds != previous_regs.ds });
+    m_registers.append({ "es", current_regs.es, current_regs.es != previous_regs.es });
+    m_registers.append({ "fs", current_regs.fs, current_regs.ds != previous_regs.fs });
+    m_registers.append({ "gs", current_regs.gs, current_regs.gs != previous_regs.gs });
+}
+
+RegistersModel::~RegistersModel()
+{
+}
+
+int RegistersModel::row_count(const GUI::ModelIndex&) const
+{
+    return m_registers.size();
+}
+
+String RegistersModel::column_name(int column) const
+{
+    switch (column) {
+    case Column::Register:
+        return "Register";
+    case Column::Value:
+        return "Value";
+    default:
+        ASSERT_NOT_REACHED();
+        return {};
+    }
+}
+
+GUI::Variant RegistersModel::data(const GUI::ModelIndex& index, GUI::ModelRole role) const
+{
+    auto& reg = m_registers[index.row()];
+
+    if (role == GUI::ModelRole::ForegroundColor) {
+        if (reg.changed)
+            return Color(Color::Red);
+        else
+            return Color(Color::Black);
+    }
+
+    if (role == GUI::ModelRole::Display) {
+        if (index.column() == Column::Register)
+            return reg.name;
+        if (index.column() == Column::Value)
+            return String::formatted("{:08x}", reg.value);
+        return {};
+    }
+    return {};
+}
+
+void RegistersModel::update()
+{
+    did_update();
+}
+
+}

Userland/DevTools/HackStudio/Debugger/RegistersModel.h

@@ -0,0 +1,77 @@
+/*
+ * Copyright (c) 2020, Luke Wilde <luke.wilde@live.co.uk>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <AK/Vector.h>
+#include <LibGUI/Model.h>
+#include <sys/arch/i386/regs.h>
+
+namespace HackStudio {
+
+struct RegisterData {
+    String name;
+    u32 value;
+    bool changed { false };
+};
+
+class RegistersModel final : public GUI::Model {
+public:
+    static RefPtr<RegistersModel> create(const PtraceRegisters& regs)
+    {
+        return adopt(*new RegistersModel(regs));
+    }
+
+    static RefPtr<RegistersModel> create(const PtraceRegisters& current_regs, const PtraceRegisters& previous_regs)
+    {
+        return adopt(*new RegistersModel(current_regs, previous_regs));
+    }
+
+    enum Column {
+        Register,
+        Value,
+        __Count
+    };
+
+    virtual ~RegistersModel() override;
+
+    virtual int row_count(const GUI::ModelIndex& = GUI::ModelIndex()) const override;
+    virtual int column_count(const GUI::ModelIndex& = GUI::ModelIndex()) const override { return Column::__Count; }
+    virtual String column_name(int) const override;
+    virtual GUI::Variant data(const GUI::ModelIndex&, GUI::ModelRole) const override;
+    virtual void update() override;
+
+    const PtraceRegisters& raw_registers() const { return m_raw_registers; }
+
+private:
+    explicit RegistersModel(const PtraceRegisters& regs);
+    RegistersModel(const PtraceRegisters& current_regs, const PtraceRegisters& previous_regs);
+
+    PtraceRegisters m_raw_registers;
+    Vector<RegisterData> m_registers;
+};
+
+}

Userland/DevTools/HackStudio/Debugger/VariablesModel.cpp

@@ -0,0 +1,194 @@
+/*
+ * Copyright (c) 2020, Itamar S. <itamar8910@gmail.com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "VariablesModel.h"
+#include <LibGUI/Application.h>
+#include <LibGUI/MessageBox.h>
+
+namespace HackStudio {
+
+GUI::ModelIndex VariablesModel::index(int row, int column, const GUI::ModelIndex& parent_index) const
+{
+    if (!parent_index.is_valid())
+        return create_index(row, column, &m_variables[row]);
+    auto* parent = static_cast<const Debug::DebugInfo::VariableInfo*>(parent_index.internal_data());
+    auto* child = &parent->members[row];
+    return create_index(row, column, child);
+}
+
+GUI::ModelIndex VariablesModel::parent_index(const GUI::ModelIndex& index) const
+{
+    if (!index.is_valid())
+        return {};
+    auto* child = static_cast<const Debug::DebugInfo::VariableInfo*>(index.internal_data());
+    auto* parent = child->parent;
+    if (parent == nullptr)
+        return {};
+
+    if (parent->parent == nullptr) {
+        for (size_t row = 0; row < m_variables.size(); row++)
+            if (m_variables.ptr_at(row).ptr() == parent)
+                return create_index(row, 0, parent);
+        ASSERT_NOT_REACHED();
+    }
+    for (size_t row = 0; row < parent->parent->members.size(); row++) {
+        Debug::DebugInfo::VariableInfo* child_at_row = parent->parent->members.ptr_at(row).ptr();
+        if (child_at_row == parent)
+            return create_index(row, 0, parent);
+    }
+    ASSERT_NOT_REACHED();
+}
+
+int VariablesModel::row_count(const GUI::ModelIndex& index) const
+{
+    if (!index.is_valid())
+        return m_variables.size();
+    auto* node = static_cast<const Debug::DebugInfo::VariableInfo*>(index.internal_data());
+    return node->members.size();
+}
+
+static String variable_value_as_string(const Debug::DebugInfo::VariableInfo& variable)
+{
+    if (variable.location_type != Debug::DebugInfo::VariableInfo::LocationType::Address)
+        return "N/A";
+
+    auto variable_address = variable.location_data.address;
+
+    if (variable.is_enum_type()) {
+        auto value = Debugger::the().session()->peek((u32*)variable_address);
+        ASSERT(value.has_value());
+        auto it = variable.type->members.find_if([&enumerator_value = value.value()](const auto& enumerator) {
+            return enumerator->constant_data.as_u32 == enumerator_value;
+        });
+        ASSERT(!it.is_end());
+        return String::formatted("{}::{}", variable.type_name, (*it)->name);
+    }
+
+    if (variable.type_name == "int") {
+        auto value = Debugger::the().session()->peek((u32*)variable_address);
+        ASSERT(value.has_value());
+        return String::formatted("{}", static_cast<int>(value.value()));
+    }
+
+    if (variable.type_name == "char") {
+        auto value = Debugger::the().session()->peek((u32*)variable_address);
+        ASSERT(value.has_value());
+        return String::formatted("'{0:c}' ({0:d})", value.value());
+    }
+
+    if (variable.type_name == "bool") {
+        auto value = Debugger::the().session()->peek((u32*)variable_address);
+        ASSERT(value.has_value());
+        return (value.value() & 1) ? "true" : "false";
+    }
+
+    return String::formatted("type: {} @ {:p}, ", variable.type_name, variable_address);
+}
+
+static Optional<u32> string_to_variable_value(const StringView& string_value, const Debug::DebugInfo::VariableInfo& variable)
+{
+    if (variable.is_enum_type()) {
+        auto prefix_string = String::formatted("{}::", variable.type_name);
+        auto string_to_use = string_value;
+        if (string_value.starts_with(prefix_string))
+            string_to_use = string_value.substring_view(prefix_string.length(), string_value.length() - prefix_string.length());
+
+        auto it = variable.type->members.find_if([string_to_use](const auto& enumerator) {
+            return enumerator->name == string_to_use;
+        });
+
+        if (it.is_end())
+            return {};
+        return (*it)->constant_data.as_u32;
+    }
+
+    if (variable.type_name == "int") {
+        auto value = string_value.to_int();
+        if (value.has_value())
+            return value.value();
+        return {};
+    }
+
+    if (variable.type_name == "bool") {
+        if (string_value == "true")
+            return true;
+        if (string_value == "false")
+            return false;
+        return {};
+    }
+
+    return {};
+}
+
+void VariablesModel::set_variable_value(const GUI::ModelIndex& index, const StringView& string_value, GUI::Window* parent_window)
+{
+    auto variable = static_cast<const Debug::DebugInfo::VariableInfo*>(index.internal_data());
+
+    auto value = string_to_variable_value(string_value, *variable);
+
+    if (value.has_value()) {
+        auto success = Debugger::the().session()->poke((u32*)variable->location_data.address, value.value());
+        ASSERT(success);
+        return;
+    }
+
+    GUI::MessageBox::show(
+        parent_window,
+        String::formatted("String value \"{}\" could not be converted to a value of type {}.", string_value, variable->type_name),
+        "Set value failed",
+        GUI::MessageBox::Type::Error);
+}
+
+GUI::Variant VariablesModel::data(const GUI::ModelIndex& index, GUI::ModelRole role) const
+{
+    auto* variable = static_cast<const Debug::DebugInfo::VariableInfo*>(index.internal_data());
+    switch (role) {
+    case GUI::ModelRole::Display: {
+        auto value_as_string = variable_value_as_string(*variable);
+        return String::formatted("{}: {}", variable->name, value_as_string);
+    }
+    case GUI::ModelRole::Icon:
+        return m_variable_icon;
+    default:
+        return {};
+    }
+}
+
+void VariablesModel::update()
+{
+    did_update();
+}
+
+RefPtr<VariablesModel> VariablesModel::create(const PtraceRegisters& regs)
+{
+    auto lib = Debugger::the().session()->library_at(regs.eip);
+    if (!lib)
+        return nullptr;
+    auto variables = lib->debug_info->get_variables_in_current_scope(regs);
+    return adopt(*new VariablesModel(move(variables), regs));
+}
+
+}

Userland/DevTools/HackStudio/Debugger/VariablesModel.h

@@ -0,0 +1,63 @@
+/*
+ * Copyright (c) 2020, Itamar S. <itamar8910@gmail.com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include "Debugger.h"
+#include <AK/NonnullOwnPtr.h>
+#include <LibGUI/Model.h>
+#include <LibGUI/TreeView.h>
+#include <sys/arch/i386/regs.h>
+
+namespace HackStudio {
+
+class VariablesModel final : public GUI::Model {
+public:
+    static RefPtr<VariablesModel> create(const PtraceRegisters& regs);
+
+    void set_variable_value(const GUI::ModelIndex&, const StringView&, GUI::Window*);
+
+    virtual int row_count(const GUI::ModelIndex& = GUI::ModelIndex()) const override;
+    virtual int column_count(const GUI::ModelIndex& = GUI::ModelIndex()) const override { return 1; }
+    virtual GUI::Variant data(const GUI::ModelIndex& index, GUI::ModelRole role) const override;
+    virtual void update() override;
+    virtual GUI::ModelIndex parent_index(const GUI::ModelIndex&) const override;
+    virtual GUI::ModelIndex index(int row, int column = 0, const GUI::ModelIndex& = GUI::ModelIndex()) const override;
+
+private:
+    explicit VariablesModel(NonnullOwnPtrVector<Debug::DebugInfo::VariableInfo>&& variables, const PtraceRegisters& regs)
+        : m_variables(move(variables))
+        , m_regs(regs)
+    {
+        m_variable_icon.set_bitmap_for_size(16, Gfx::Bitmap::load_from_file("/res/icons/16x16/inspector-object.png"));
+    }
+    NonnullOwnPtrVector<Debug::DebugInfo::VariableInfo> m_variables;
+    PtraceRegisters m_regs;
+
+    GUI::Icon m_variable_icon;
+};
+
+}

Userland/DevTools/HackStudio/Editor.cpp

@@ -0,0 +1,530 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "Editor.h"
+#include "Debugger/Debugger.h"
+#include "EditorWrapper.h"
+#include "HackStudio.h"
+#include "Language.h"
+#include <AK/ByteBuffer.h>
+#include <AK/LexicalPath.h>
+#include <LibCore/DirIterator.h>
+#include <LibCore/File.h>
+#include <LibGUI/Application.h>
+#include <LibGUI/CppSyntaxHighlighter.h>
+#include <LibGUI/GMLSyntaxHighlighter.h>
+#include <LibGUI/INISyntaxHighlighter.h>
+#include <LibGUI/JSSyntaxHighlighter.h>
+#include <LibGUI/Label.h>
+#include <LibGUI/Painter.h>
+#include <LibGUI/ScrollBar.h>
+#include <LibGUI/ShellSyntaxHighlighter.h>
+#include <LibGUI/SyntaxHighlighter.h>
+#include <LibGUI/Window.h>
+#include <LibMarkdown/Document.h>
+#include <LibWeb/DOM/ElementFactory.h>
+#include <LibWeb/DOM/Text.h>
+#include <LibWeb/HTML/HTMLHeadElement.h>
+#include <LibWeb/OutOfProcessWebView.h>
+#include <fcntl.h>
+
+// #define EDITOR_DEBUG
+
+namespace HackStudio {
+
+Editor::Editor()
+{
+    set_document(CodeDocument::create());
+    m_documentation_tooltip_window = GUI::Window::construct();
+    m_documentation_tooltip_window->set_rect(0, 0, 500, 400);
+    m_documentation_tooltip_window->set_window_type(GUI::WindowType::Tooltip);
+    m_documentation_page_view = m_documentation_tooltip_window->set_main_widget<Web::OutOfProcessWebView>();
+}
+
+Editor::~Editor()
+{
+}
+
+EditorWrapper& Editor::wrapper()
+{
+    return static_cast<EditorWrapper&>(*parent());
+}
+const EditorWrapper& Editor::wrapper() const
+{
+    return static_cast<const EditorWrapper&>(*parent());
+}
+
+void Editor::focusin_event(GUI::FocusEvent& event)
+{
+    wrapper().set_editor_has_focus({}, true);
+    if (on_focus)
+        on_focus();
+    GUI::TextEditor::focusin_event(event);
+}
+
+void Editor::focusout_event(GUI::FocusEvent& event)
+{
+    wrapper().set_editor_has_focus({}, false);
+    GUI::TextEditor::focusout_event(event);
+}
+
+Gfx::IntRect Editor::breakpoint_icon_rect(size_t line_number) const
+{
+    auto ruler_line_rect = ruler_content_rect(line_number);
+
+    auto scroll_value = vertical_scrollbar().value();
+    ruler_line_rect = ruler_line_rect.translated({ 0, -scroll_value });
+    auto center = ruler_line_rect.center().translated({ ruler_line_rect.width() - 10, -line_spacing() - 3 });
+    constexpr int size = 32;
+    return { center.x() - size / 2, center.y() - size / 2, size, size };
+}
+
+void Editor::paint_event(GUI::PaintEvent& event)
+{
+    GUI::TextEditor::paint_event(event);
+
+    GUI::Painter painter(*this);
+    if (is_focused()) {
+        painter.add_clip_rect(event.rect());
+
+        auto rect = frame_inner_rect();
+        if (vertical_scrollbar().is_visible())
+            rect.set_width(rect.width() - vertical_scrollbar().width());
+        if (horizontal_scrollbar().is_visible())
+            rect.set_height(rect.height() - horizontal_scrollbar().height());
+        painter.draw_rect(rect, palette().selection());
+    }
+
+    if (ruler_visible()) {
+        size_t first_visible_line = text_position_at(event.rect().top_left()).line();
+        size_t last_visible_line = text_position_at(event.rect().bottom_right()).line();
+        for (size_t line : breakpoint_lines()) {
+            if (line < first_visible_line || line > last_visible_line) {
+                continue;
+            }
+            const auto& icon = breakpoint_icon_bitmap();
+            painter.blit(breakpoint_icon_rect(line).center(), icon, icon.rect());
+        }
+        if (execution_position().has_value()) {
+            const auto& icon = current_position_icon_bitmap();
+            painter.blit(breakpoint_icon_rect(execution_position().value()).center(), icon, icon.rect());
+        }
+    }
+}
+
+static HashMap<String, String>& man_paths()
+{
+    static HashMap<String, String> paths;
+    if (paths.is_empty()) {
+        // FIXME: This should also search man3, possibly other places..
+        Core::DirIterator it("/usr/share/man/man2", Core::DirIterator::Flags::SkipDots);
+        while (it.has_next()) {
+            auto path = String::formatted("/usr/share/man/man2/{}", it.next_path());
+            auto title = LexicalPath(path).title();
+            paths.set(title, path);
+        }
+    }
+
+    return paths;
+}
+
+void Editor::show_documentation_tooltip_if_available(const String& hovered_token, const Gfx::IntPoint& screen_location)
+{
+    auto it = man_paths().find(hovered_token);
+    if (it == man_paths().end()) {
+#ifdef EDITOR_DEBUG
+        dbgln("no man path for {}", hovered_token);
+#endif
+        m_documentation_tooltip_window->hide();
+        return;
+    }
+
+    if (m_documentation_tooltip_window->is_visible() && hovered_token == m_last_parsed_token) {
+        return;
+    }
+
+#ifdef EDITOR_DEBUG
+    dbgln("opening {}", it->value);
+#endif
+    auto file = Core::File::construct(it->value);
+    if (!file->open(Core::File::ReadOnly)) {
+        dbgln("failed to open {}, {}", it->value, file->error_string());
+        return;
+    }
+
+    auto man_document = Markdown::Document::parse(file->read_all());
+
+    if (!man_document) {
+        dbgln("failed to parse markdown");
+        return;
+    }
+
+    StringBuilder html;
+    // FIXME: With the InProcessWebView we used to manipulate the document body directly,
+    // With OutOfProcessWebView this isn't possible (at the moment). The ideal solution
+    // is probably to tweak Markdown::Document::render_to_html() so we can inject styles
+    // into the rendered HTML easily.
+    html.append(man_document->render_to_html());
+    html.append("<style>body { background-color: #dac7b5; }</style>");
+    m_documentation_page_view->load_html(html.build(), {});
+
+    m_documentation_tooltip_window->move_to(screen_location.translated(4, 4));
+    m_documentation_tooltip_window->show();
+
+    m_last_parsed_token = hovered_token;
+}
+
+void Editor::mousemove_event(GUI::MouseEvent& event)
+{
+    GUI::TextEditor::mousemove_event(event);
+
+    if (document().spans().is_empty())
+        return;
+
+    auto text_position = text_position_at(event.position());
+    if (!text_position.is_valid()) {
+        m_documentation_tooltip_window->hide();
+        return;
+    }
+
+    auto highlighter = wrapper().editor().syntax_highlighter();
+    if (!highlighter)
+        return;
+
+    bool hide_tooltip = true;
+    bool is_over_link = false;
+
+    auto ruler_line_rect = ruler_content_rect(text_position.line());
+    auto hovering_lines_ruler = (event.position().x() < ruler_line_rect.width());
+    if (hovering_lines_ruler && !is_in_drag_select())
+        set_override_cursor(Gfx::StandardCursor::Arrow);
+    else if (m_hovering_editor)
+        set_override_cursor(m_hovering_link && event.ctrl() ? Gfx::StandardCursor::Hand : Gfx::StandardCursor::IBeam);
+
+    for (auto& span : document().spans()) {
+        if (span.range.contains(m_previous_text_position) && !span.range.contains(text_position)) {
+            if (highlighter->is_navigatable(span.data) && span.attributes.underline) {
+                span.attributes.underline = false;
+                wrapper().editor().update();
+            }
+        }
+
+        if (span.range.contains(text_position)) {
+            auto adjusted_range = span.range;
+            auto end_line_length = document().line(span.range.end().line()).length();
+            adjusted_range.end().set_column(min(end_line_length, adjusted_range.end().column() + 1));
+            auto hovered_span_text = document().text_in_range(adjusted_range);
+#ifdef EDITOR_DEBUG
+            dbgln("Hovering: {} \"{}\"", adjusted_range, hovered_span_text);
+#endif
+
+            if (highlighter->is_navigatable(span.data)) {
+                is_over_link = true;
+                bool was_underlined = span.attributes.underline;
+                span.attributes.underline = event.modifiers() & Mod_Ctrl;
+                if (span.attributes.underline != was_underlined) {
+                    wrapper().editor().update();
+                }
+            }
+            if (highlighter->is_identifier(span.data)) {
+                show_documentation_tooltip_if_available(hovered_span_text, event.position().translated(screen_relative_rect().location()));
+                hide_tooltip = false;
+            }
+        }
+    }
+
+    m_previous_text_position = text_position;
+    if (hide_tooltip)
+        m_documentation_tooltip_window->hide();
+
+    m_hovering_link = is_over_link && (event.modifiers() & Mod_Ctrl);
+}
+
+void Editor::mousedown_event(GUI::MouseEvent& event)
+{
+    auto highlighter = wrapper().editor().syntax_highlighter();
+    if (!highlighter) {
+        GUI::TextEditor::mousedown_event(event);
+        return;
+    }
+
+    auto text_position = text_position_at(event.position());
+    auto ruler_line_rect = ruler_content_rect(text_position.line());
+    if (event.button() == GUI::MouseButton::Left && event.position().x() < ruler_line_rect.width()) {
+        if (!breakpoint_lines().contains_slow(text_position.line())) {
+            breakpoint_lines().append(text_position.line());
+            Debugger::on_breakpoint_change(wrapper().filename_label().text(), text_position.line(), BreakpointChange::Added);
+        } else {
+            breakpoint_lines().remove_first_matching([&](size_t line) { return line == text_position.line(); });
+            Debugger::on_breakpoint_change(wrapper().filename_label().text(), text_position.line(), BreakpointChange::Removed);
+        }
+    }
+
+    if (!(event.modifiers() & Mod_Ctrl)) {
+        GUI::TextEditor::mousedown_event(event);
+        return;
+    }
+
+    if (!text_position.is_valid()) {
+        GUI::TextEditor::mousedown_event(event);
+        return;
+    }
+
+    if (auto* span = document().span_at(text_position)) {
+        if (!highlighter->is_navigatable(span->data)) {
+            GUI::TextEditor::mousedown_event(event);
+            return;
+        }
+
+        auto adjusted_range = span->range;
+        adjusted_range.end().set_column(adjusted_range.end().column() + 1);
+        auto span_text = document().text_in_range(adjusted_range);
+        auto header_path = span_text.substring(1, span_text.length() - 2);
+#ifdef EDITOR_DEBUG
+        dbgln("Ctrl+click: {} \"{}\"", adjusted_range, header_path);
+#endif
+        navigate_to_include_if_available(header_path);
+        return;
+    }
+
+    GUI::TextEditor::mousedown_event(event);
+}
+
+void Editor::enter_event(Core::Event& event)
+{
+    m_hovering_editor = true;
+    GUI::TextEditor::enter_event(event);
+}
+
+void Editor::leave_event(Core::Event& event)
+{
+    m_hovering_editor = false;
+    GUI::TextEditor::leave_event(event);
+}
+
+static HashMap<String, String>& include_paths()
+{
+    static HashMap<String, String> paths;
+
+    auto add_directory = [](String base, Optional<String> recursive, auto handle_directory) -> void {
+        Core::DirIterator it(recursive.value_or(base), Core::DirIterator::Flags::SkipDots);
+        while (it.has_next()) {
+            auto path = it.next_full_path();
+            if (!Core::File::is_directory(path)) {
+                auto key = path.substring(base.length() + 1, path.length() - base.length() - 1);
+#ifdef EDITOR_DEBUG
+                dbgln("Adding header \"{}\" in path \"{}\"", key, path);
+#endif
+                paths.set(key, path);
+            } else {
+                handle_directory(base, path, handle_directory);
+            }
+        }
+    };
+
+    if (paths.is_empty()) {
+        add_directory(".", {}, add_directory);
+        add_directory("/usr/local/include", {}, add_directory);
+        add_directory("/usr/local/include/c++/9.2.0", {}, add_directory);
+        add_directory("/usr/include", {}, add_directory);
+    }
+
+    return paths;
+}
+
+void Editor::navigate_to_include_if_available(String path)
+{
+    auto it = include_paths().find(path);
+    if (it == include_paths().end()) {
+#ifdef EDITOR_DEBUG
+        dbgln("no header {} found.", path);
+#endif
+        return;
+    }
+
+    on_open(it->value);
+}
+
+void Editor::set_execution_position(size_t line_number)
+{
+    code_document().set_execution_position(line_number);
+    scroll_position_into_view({ line_number, 0 });
+    update(breakpoint_icon_rect(line_number));
+}
+
+void Editor::clear_execution_position()
+{
+    if (!execution_position().has_value()) {
+        return;
+    }
+    size_t previous_position = execution_position().value();
+    code_document().clear_execution_position();
+    update(breakpoint_icon_rect(previous_position));
+}
+
+const Gfx::Bitmap& Editor::breakpoint_icon_bitmap()
+{
+    static auto bitmap = Gfx::Bitmap::load_from_file("/res/icons/16x16/breakpoint.png");
+    return *bitmap;
+}
+
+const Gfx::Bitmap& Editor::current_position_icon_bitmap()
+{
+    static auto bitmap = Gfx::Bitmap::load_from_file("/res/icons/16x16/go-forward.png");
+    return *bitmap;
+}
+
+const CodeDocument& Editor::code_document() const
+{
+    const auto& doc = document();
+    ASSERT(doc.is_code_document());
+    return static_cast<const CodeDocument&>(doc);
+}
+
+CodeDocument& Editor::code_document()
+{
+    return const_cast<CodeDocument&>(static_cast<const Editor&>(*this).code_document());
+}
+
+void Editor::set_document(GUI::TextDocument& doc)
+{
+    ASSERT(doc.is_code_document());
+    GUI::TextEditor::set_document(doc);
+
+    set_override_cursor(Gfx::StandardCursor::IBeam);
+
+    CodeDocument& code_document = static_cast<CodeDocument&>(doc);
+    switch (code_document.language()) {
+    case Language::Cpp:
+        set_syntax_highlighter(make<GUI::CppSyntaxHighlighter>());
+        m_language_client = get_language_client<LanguageClients::Cpp::ServerConnection>(project().root_path());
+        break;
+    case Language::GML:
+        set_syntax_highlighter(make<GUI::GMLSyntaxHighlighter>());
+        break;
+    case Language::JavaScript:
+        set_syntax_highlighter(make<GUI::JSSyntaxHighlighter>());
+        break;
+    case Language::Ini:
+        set_syntax_highlighter(make<GUI::IniSyntaxHighlighter>());
+        break;
+    case Language::Shell:
+        set_syntax_highlighter(make<GUI::ShellSyntaxHighlighter>());
+        m_language_client = get_language_client<LanguageClients::Shell::ServerConnection>(project().root_path());
+        break;
+    default:
+        set_syntax_highlighter({});
+    }
+
+    if (m_language_client) {
+        set_autocomplete_provider(make<LanguageServerAidedAutocompleteProvider>(*m_language_client));
+        dbgln("Opening {}", code_document.file_path());
+        int fd = open(code_document.file_path().characters(), O_RDONLY | O_NOCTTY);
+        if (fd < 0) {
+            perror("open");
+            return;
+        }
+        m_language_client->open_file(code_document.file_path(), fd);
+        close(fd);
+    }
+}
+
+Optional<Editor::AutoCompleteRequestData> Editor::get_autocomplete_request_data()
+{
+    if (!wrapper().editor().m_language_client)
+        return {};
+
+    return Editor::AutoCompleteRequestData { cursor() };
+}
+
+void Editor::LanguageServerAidedAutocompleteProvider::provide_completions(Function<void(Vector<Entry>)> callback)
+{
+    auto& editor = static_cast<Editor&>(*m_editor).wrapper().editor();
+    auto data = editor.get_autocomplete_request_data();
+    if (!data.has_value())
+        callback({});
+
+    m_language_client.on_autocomplete_suggestions = [callback = move(callback)](auto suggestions) {
+        callback(suggestions);
+    };
+
+    m_language_client.request_autocomplete(
+        editor.code_document().file_path(),
+        data.value().position.line(),
+        data.value().position.column());
+}
+
+void Editor::on_edit_action(const GUI::Command& command)
+{
+    if (!m_language_client)
+        return;
+
+    if (command.is_insert_text()) {
+        const GUI::InsertTextCommand& insert_command = static_cast<const GUI::InsertTextCommand&>(command);
+        m_language_client->insert_text(
+            code_document().file_path(),
+            insert_command.text(),
+            insert_command.range().start().line(),
+            insert_command.range().start().column());
+        return;
+    }
+
+    if (command.is_remove_text()) {
+        const GUI::RemoveTextCommand& remove_command = static_cast<const GUI::RemoveTextCommand&>(command);
+        m_language_client->remove_text(
+            code_document().file_path(),
+            remove_command.range().start().line(),
+            remove_command.range().start().column(),
+            remove_command.range().end().line(),
+            remove_command.range().end().column());
+        return;
+    }
+
+    ASSERT_NOT_REACHED();
+}
+
+void Editor::undo()
+{
+    TextEditor::undo();
+    flush_file_content_to_langauge_server();
+}
+
+void Editor::redo()
+{
+    TextEditor::redo();
+    flush_file_content_to_langauge_server();
+}
+
+void Editor::flush_file_content_to_langauge_server()
+{
+    if (!m_language_client)
+        return;
+
+    m_language_client->set_file_content(
+        code_document().file_path(),
+        document().text());
+}
+}

Userland/DevTools/HackStudio/Editor.h

@@ -0,0 +1,118 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include "CodeDocument.h"
+#include "Debugger/BreakpointCallback.h"
+#include "LanguageClient.h"
+#include <AK/Optional.h>
+#include <AK/OwnPtr.h>
+#include <LibGUI/TextEditor.h>
+#include <LibWeb/Forward.h>
+
+namespace HackStudio {
+
+class EditorWrapper;
+
+class Editor final : public GUI::TextEditor {
+    C_OBJECT(Editor)
+public:
+    virtual ~Editor() override;
+
+    Function<void()> on_focus;
+    Function<void(String)> on_open;
+
+    EditorWrapper& wrapper();
+    const EditorWrapper& wrapper() const;
+
+    const Vector<size_t>& breakpoint_lines() const { return code_document().breakpoint_lines(); }
+    Vector<size_t>& breakpoint_lines() { return code_document().breakpoint_lines(); }
+    Optional<size_t> execution_position() const { return code_document().execution_position(); }
+    void set_execution_position(size_t line_number);
+    void clear_execution_position();
+
+    const CodeDocument& code_document() const;
+    CodeDocument& code_document();
+
+    virtual void set_document(GUI::TextDocument&) override;
+
+    virtual void on_edit_action(const GUI::Command&) override;
+
+    virtual void undo() override;
+    virtual void redo() override;
+
+private:
+    virtual void focusin_event(GUI::FocusEvent&) override;
+    virtual void focusout_event(GUI::FocusEvent&) override;
+    virtual void paint_event(GUI::PaintEvent&) override;
+    virtual void mousemove_event(GUI::MouseEvent&) override;
+    virtual void mousedown_event(GUI::MouseEvent&) override;
+    virtual void enter_event(Core::Event&) override;
+    virtual void leave_event(Core::Event&) override;
+
+    void show_documentation_tooltip_if_available(const String&, const Gfx::IntPoint& screen_location);
+    void navigate_to_include_if_available(String);
+
+    Gfx::IntRect breakpoint_icon_rect(size_t line_number) const;
+    static const Gfx::Bitmap& breakpoint_icon_bitmap();
+    static const Gfx::Bitmap& current_position_icon_bitmap();
+
+    struct AutoCompleteRequestData {
+        GUI::TextPosition position;
+    };
+
+    class LanguageServerAidedAutocompleteProvider final : virtual public GUI::AutocompleteProvider {
+    public:
+        LanguageServerAidedAutocompleteProvider(LanguageClient& client)
+            : m_language_client(client)
+        {
+        }
+        virtual ~LanguageServerAidedAutocompleteProvider() override { }
+
+    private:
+        virtual void provide_completions(Function<void(Vector<Entry>)> callback) override;
+        LanguageClient& m_language_client;
+    };
+
+    Optional<AutoCompleteRequestData> get_autocomplete_request_data();
+
+    void flush_file_content_to_langauge_server();
+
+    explicit Editor();
+
+    RefPtr<GUI::Window> m_documentation_tooltip_window;
+    RefPtr<Web::OutOfProcessWebView> m_documentation_page_view;
+    String m_last_parsed_token;
+    GUI::TextPosition m_previous_text_position { 0, 0 };
+    bool m_hovering_editor { false };
+    bool m_hovering_link { false };
+    bool m_autocomplete_in_focus { false };
+
+    OwnPtr<LanguageClient> m_language_client;
+};
+
+}

Userland/DevTools/HackStudio/EditorWrapper.cpp

@@ -0,0 +1,84 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "EditorWrapper.h"
+#include "Editor.h"
+#include "HackStudio.h"
+#include <LibGUI/Action.h>
+#include <LibGUI/BoxLayout.h>
+#include <LibGUI/InputBox.h>
+#include <LibGUI/Label.h>
+#include <LibGfx/Font.h>
+#include <LibGfx/FontDatabase.h>
+
+namespace HackStudio {
+
+EditorWrapper::EditorWrapper()
+{
+    set_layout<GUI::VerticalBoxLayout>();
+
+    auto& label_wrapper = add<GUI::Widget>();
+    label_wrapper.set_fixed_height(14);
+    label_wrapper.set_fill_with_background_color(true);
+    label_wrapper.set_layout<GUI::HorizontalBoxLayout>();
+    label_wrapper.layout()->set_margins({ 2, 0, 2, 0 });
+
+    m_filename_label = label_wrapper.add<GUI::Label>("(Untitled)");
+    m_filename_label->set_text_alignment(Gfx::TextAlignment::CenterLeft);
+    m_filename_label->set_fixed_height(14);
+
+    m_cursor_label = label_wrapper.add<GUI::Label>("(Cursor)");
+    m_cursor_label->set_text_alignment(Gfx::TextAlignment::CenterRight);
+    m_cursor_label->set_fixed_height(14);
+
+    m_editor = add<Editor>();
+    m_editor->set_ruler_visible(true);
+    m_editor->set_line_wrapping_enabled(true);
+    m_editor->set_automatic_indentation_enabled(true);
+
+    m_editor->on_cursor_change = [this] {
+        m_cursor_label->set_text(String::formatted("Line: {}, Column: {}", m_editor->cursor().line() + 1, m_editor->cursor().column()));
+    };
+
+    m_editor->on_focus = [this] {
+        set_current_editor_wrapper(this);
+    };
+
+    m_editor->on_open = [](String path) {
+        open_file(path);
+    };
+}
+
+EditorWrapper::~EditorWrapper()
+{
+}
+
+void EditorWrapper::set_editor_has_focus(Badge<Editor>, bool focus)
+{
+    m_filename_label->set_font(focus ? Gfx::FontDatabase::default_bold_font() : Gfx::FontDatabase::default_font());
+}
+
+}

Userland/DevTools/HackStudio/EditorWrapper.h

@@ -0,0 +1,60 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include "Debugger/BreakpointCallback.h"
+#include <AK/Function.h>
+#include <AK/Vector.h>
+#include <LibGUI/Widget.h>
+#include <string.h>
+
+namespace HackStudio {
+
+class Editor;
+
+class EditorWrapper : public GUI::Widget {
+    C_OBJECT(EditorWrapper)
+public:
+    virtual ~EditorWrapper() override;
+
+    Editor& editor() { return *m_editor; }
+    const Editor& editor() const { return *m_editor; }
+
+    GUI::Label& filename_label() { return *m_filename_label; }
+    const GUI::Label& filename_label() const { return *m_filename_label; }
+
+    void set_editor_has_focus(Badge<Editor>, bool);
+
+private:
+    EditorWrapper();
+
+    RefPtr<GUI::Label> m_filename_label;
+    RefPtr<GUI::Label> m_cursor_label;
+    RefPtr<Editor> m_editor;
+};
+
+}

Userland/DevTools/HackStudio/FindInFilesWidget.cpp

@@ -0,0 +1,173 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "FindInFilesWidget.h"
+#include "HackStudio.h"
+#include "Project.h"
+#include <AK/StringBuilder.h>
+#include <LibGUI/BoxLayout.h>
+#include <LibGUI/Button.h>
+#include <LibGUI/TableView.h>
+#include <LibGUI/TextBox.h>
+#include <LibGfx/FontDatabase.h>
+
+namespace HackStudio {
+
+struct Match {
+    String filename;
+    GUI::TextRange range;
+    String text;
+};
+
+class SearchResultsModel final : public GUI::Model {
+public:
+    enum Column {
+        Filename,
+        Location,
+        MatchedText,
+        __Count
+    };
+
+    explicit SearchResultsModel(const Vector<Match>&& matches)
+        : m_matches(move(matches))
+    {
+    }
+
+    virtual int row_count(const GUI::ModelIndex& = GUI::ModelIndex()) const override { return m_matches.size(); }
+    virtual int column_count(const GUI::ModelIndex& = GUI::ModelIndex()) const override { return Column::__Count; }
+
+    virtual String column_name(int column) const override
+    {
+        switch (column) {
+        case Column::Filename:
+            return "Filename";
+        case Column::Location:
+            return "#";
+        case Column::MatchedText:
+            return "Text";
+        default:
+            ASSERT_NOT_REACHED();
+        }
+    }
+
+    virtual GUI::Variant data(const GUI::ModelIndex& index, GUI::ModelRole role) const override
+    {
+        if (role == GUI::ModelRole::TextAlignment)
+            return Gfx::TextAlignment::CenterLeft;
+        if (role == GUI::ModelRole::Font) {
+            if (index.column() == Column::MatchedText)
+                return Gfx::FontDatabase::default_fixed_width_font();
+            return {};
+        }
+        if (role == GUI::ModelRole::Display) {
+            auto& match = m_matches.at(index.row());
+            switch (index.column()) {
+            case Column::Filename:
+                return match.filename;
+            case Column::Location:
+                return (int)match.range.start().line();
+            case Column::MatchedText:
+                return match.text;
+            }
+        }
+        return {};
+    }
+
+    virtual void update() override { }
+    virtual GUI::ModelIndex index(int row, int column = 0, const GUI::ModelIndex& = GUI::ModelIndex()) const override
+    {
+        if (row < 0 || row >= (int)m_matches.size())
+            return {};
+        if (column < 0 || column >= Column::__Count)
+            return {};
+        return create_index(row, column, &m_matches.at(row));
+    }
+
+private:
+    Vector<Match> m_matches;
+};
+
+static RefPtr<SearchResultsModel> find_in_files(const StringView& text)
+{
+    Vector<Match> matches;
+    project().for_each_text_file([&](auto& file) {
+        auto matches_in_file = file.document().find_all(text);
+        for (auto& range : matches_in_file) {
+            auto whole_line_range = file.document().range_for_entire_line(range.start().line());
+            auto whole_line_containing_match = file.document().text_in_range(whole_line_range);
+            auto left_part = whole_line_containing_match.substring(0, range.start().column());
+            auto right_part = whole_line_containing_match.substring(range.end().column(), whole_line_containing_match.length() - range.end().column());
+            StringBuilder builder;
+            builder.append(left_part);
+            builder.append(0x01);
+            builder.append(file.document().text_in_range(range));
+            builder.append(0x02);
+            builder.append(right_part);
+            matches.append({ file.name(), range, builder.to_string() });
+        }
+    });
+
+    return adopt(*new SearchResultsModel(move(matches)));
+}
+
+FindInFilesWidget::FindInFilesWidget()
+{
+    set_layout<GUI::VerticalBoxLayout>();
+
+    auto& top_container = add<Widget>();
+    top_container.set_layout<GUI::HorizontalBoxLayout>();
+    top_container.set_fixed_height(20);
+
+    m_textbox = top_container.add<GUI::TextBox>();
+
+    m_button = top_container.add<GUI::Button>("Find in files");
+    m_button->set_fixed_width(100);
+
+    m_result_view = add<GUI::TableView>();
+
+    m_result_view->on_activation = [](auto& index) {
+        auto& match = *(const Match*)index.internal_data();
+        open_file(match.filename);
+        current_editor().set_selection(match.range);
+        current_editor().set_focus(true);
+    };
+
+    m_button->on_click = [this](auto) {
+        auto results_model = find_in_files(m_textbox->text());
+        m_result_view->set_model(results_model);
+    };
+    m_textbox->on_return_pressed = [this] {
+        m_button->click();
+    };
+}
+
+void FindInFilesWidget::focus_textbox_and_select_all()
+{
+    m_textbox->select_all();
+    m_textbox->set_focus(true);
+}
+
+}

Userland/DevTools/HackStudio/FindInFilesWidget.h

@@ -0,0 +1,50 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <LibGUI/Button.h>
+#include <LibGUI/TextBox.h>
+#include <LibGUI/Widget.h>
+
+namespace HackStudio {
+
+class FindInFilesWidget final : public GUI::Widget {
+    C_OBJECT(FindInFilesWidget)
+public:
+    virtual ~FindInFilesWidget() override { }
+
+    void focus_textbox_and_select_all();
+
+private:
+    explicit FindInFilesWidget();
+
+    RefPtr<GUI::TextBox> m_textbox;
+    RefPtr<GUI::Button> m_button;
+    RefPtr<GUI::TableView> m_result_view;
+};
+
+}

Userland/DevTools/HackStudio/FormEditorWidget.cpp

@@ -0,0 +1,68 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "FormEditorWidget.h"
+#include "CursorTool.h"
+#include "FormWidget.h"
+#include "WidgetTreeModel.h"
+#include <LibGUI/Painter.h>
+
+namespace HackStudio {
+
+FormEditorWidget::FormEditorWidget()
+    : m_tool(make<CursorTool>(*this))
+{
+    set_fill_with_background_color(true);
+
+    m_form_widget = add<FormWidget>();
+    m_widget_tree_model = WidgetTreeModel::create(*m_form_widget);
+}
+
+FormEditorWidget::~FormEditorWidget()
+{
+}
+
+void FormEditorWidget::paint_event(GUI::PaintEvent& event)
+{
+    GUI::Frame::paint_event(event);
+
+    GUI::Painter painter(*this);
+    painter.add_clip_rect(event.rect());
+}
+
+void FormEditorWidget::set_tool(NonnullOwnPtr<Tool> tool)
+{
+    m_tool->detach();
+    m_tool = move(tool);
+    m_tool->attach();
+}
+
+WidgetTreeModel& FormEditorWidget::model()
+{
+    return *m_widget_tree_model;
+}
+
+}

Userland/DevTools/HackStudio/FormEditorWidget.h

@@ -0,0 +1,137 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <AK/HashTable.h>
+#include <LibGUI/ScrollableWidget.h>
+
+namespace HackStudio {
+
+class FormWidget;
+class Tool;
+class WidgetTreeModel;
+
+class FormEditorWidget final : public GUI::ScrollableWidget {
+    C_OBJECT(FormEditorWidget)
+public:
+    virtual ~FormEditorWidget() override;
+
+    FormWidget& form_widget() { return *m_form_widget; }
+    const FormWidget& form_widget() const { return *m_form_widget; }
+
+    Tool& tool() { return *m_tool; }
+    const Tool& tool() const { return *m_tool; }
+
+    void set_tool(NonnullOwnPtr<Tool>);
+
+    WidgetTreeModel& model();
+
+    class WidgetSelection {
+    public:
+        Function<void(GUI::Widget&)> on_remove;
+        Function<void(GUI::Widget&)> on_add;
+        Function<void()> on_clear;
+
+        void enable_hooks() { m_hooks_enabled = true; }
+        void disable_hooks() { m_hooks_enabled = false; }
+
+        bool is_empty() const
+        {
+            return m_widgets.is_empty();
+        }
+
+        bool contains(GUI::Widget& widget) const
+        {
+            return m_widgets.contains(&widget);
+        }
+
+        void toggle(GUI::Widget& widget)
+        {
+            if (contains(widget))
+                remove(widget);
+            else
+                add(widget);
+        }
+
+        void set(GUI::Widget& widget)
+        {
+            clear();
+            add(widget);
+        }
+
+        void remove(GUI::Widget& widget)
+        {
+            ASSERT(m_widgets.contains(&widget));
+            m_widgets.remove(&widget);
+            if (m_hooks_enabled && on_remove)
+                on_remove(widget);
+        }
+
+        void add(GUI::Widget& widget)
+        {
+            m_widgets.set(&widget);
+            if (m_hooks_enabled && on_add)
+                on_add(widget);
+        }
+
+        void clear()
+        {
+            m_widgets.clear();
+            if (m_hooks_enabled && on_clear)
+                on_clear();
+        }
+
+        template<typename Callback>
+        void for_each(Callback callback)
+        {
+            for (auto& it : m_widgets) {
+                if (callback(*it) == IterationDecision::Break)
+                    break;
+            }
+        }
+
+        WidgetSelection() { }
+
+    private:
+        HashTable<GUI::Widget*> m_widgets;
+        bool m_hooks_enabled { true };
+    };
+
+    WidgetSelection& selection() { return m_selection; }
+
+private:
+    virtual void paint_event(GUI::PaintEvent&) override;
+
+    FormEditorWidget();
+
+    RefPtr<FormWidget> m_form_widget;
+    RefPtr<WidgetTreeModel> m_widget_tree_model;
+    NonnullOwnPtr<Tool> m_tool;
+    WidgetSelection m_selection;
+};
+
+}

Userland/DevTools/HackStudio/FormWidget.cpp

@@ -0,0 +1,106 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "FormWidget.h"
+#include "FormEditorWidget.h"
+#include "Tool.h"
+#include <LibGUI/Painter.h>
+
+namespace HackStudio {
+
+FormWidget::FormWidget()
+{
+    set_focus_policy(GUI::FocusPolicy::StrongFocus);
+    set_fill_with_background_color(true);
+    set_relative_rect(5, 5, 400, 300);
+
+    set_greedy_for_hits(true);
+}
+
+FormWidget::~FormWidget()
+{
+}
+
+FormEditorWidget& FormWidget::editor()
+{
+    return static_cast<FormEditorWidget&>(*parent());
+}
+
+const FormEditorWidget& FormWidget::editor() const
+{
+    return static_cast<const FormEditorWidget&>(*parent());
+}
+
+void FormWidget::paint_event(GUI::PaintEvent& event)
+{
+    GUI::Painter painter(*this);
+    painter.add_clip_rect(event.rect());
+
+    for (int y = 0; y < height(); y += m_grid_size) {
+        for (int x = 0; x < width(); x += m_grid_size) {
+            painter.set_pixel({ x, y }, Color::from_rgb(0x404040));
+        }
+    }
+}
+
+void FormWidget::second_paint_event(GUI::PaintEvent& event)
+{
+    GUI::Painter painter(*this);
+    painter.add_clip_rect(event.rect());
+
+    if (!editor().selection().is_empty()) {
+        for_each_child_widget([&](auto& child) {
+            if (editor().selection().contains(child)) {
+                painter.draw_rect(child.relative_rect(), Color::Blue);
+            }
+            return IterationDecision::Continue;
+        });
+    }
+
+    editor().tool().on_second_paint(painter, event);
+}
+
+void FormWidget::mousedown_event(GUI::MouseEvent& event)
+{
+    editor().tool().on_mousedown(event);
+}
+
+void FormWidget::mouseup_event(GUI::MouseEvent& event)
+{
+    editor().tool().on_mouseup(event);
+}
+
+void FormWidget::mousemove_event(GUI::MouseEvent& event)
+{
+    editor().tool().on_mousemove(event);
+}
+
+void FormWidget::keydown_event(GUI::KeyEvent& event)
+{
+    editor().tool().on_keydown(event);
+}
+
+}

Userland/DevTools/HackStudio/FormWidget.h

@@ -0,0 +1,61 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <AK/Badge.h>
+#include <LibGUI/Widget.h>
+
+namespace HackStudio {
+
+class CursorTool;
+class FormEditorWidget;
+
+class FormWidget final : public GUI::Widget {
+    C_OBJECT(FormWidget)
+public:
+    virtual ~FormWidget() override;
+
+    FormEditorWidget& editor();
+    const FormEditorWidget& editor() const;
+
+    // FIXME: This should be an app-wide preference instead.
+    int grid_size() const { return m_grid_size; }
+
+private:
+    virtual void paint_event(GUI::PaintEvent&) override;
+    virtual void second_paint_event(GUI::PaintEvent&) override;
+    virtual void mousedown_event(GUI::MouseEvent&) override;
+    virtual void mouseup_event(GUI::MouseEvent&) override;
+    virtual void mousemove_event(GUI::MouseEvent&) override;
+    virtual void keydown_event(GUI::KeyEvent&) override;
+
+    FormWidget();
+
+    int m_grid_size { 5 };
+};
+
+}

Userland/DevTools/HackStudio/Git/DiffViewer.cpp

@@ -0,0 +1,253 @@
+/*
+ * Copyright (c) 2020, Itamar S. <itamar8910@gmail.com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "DiffViewer.h"
+#include <LibDiff/Hunks.h>
+#include <LibGUI/AbstractView.h>
+#include <LibGUI/Painter.h>
+#include <LibGUI/ScrollBar.h>
+#include <LibGfx/Color.h>
+#include <LibGfx/Font.h>
+#include <LibGfx/FontDatabase.h>
+#include <LibGfx/Palette.h>
+
+// #define DEBUG_DIFF
+
+namespace HackStudio {
+
+DiffViewer::~DiffViewer()
+{
+}
+
+void DiffViewer::paint_event(GUI::PaintEvent& event)
+{
+    GUI::Painter painter(*this);
+    painter.add_clip_rect(widget_inner_rect());
+    painter.add_clip_rect(event.rect());
+    painter.fill_rect(event.rect(), palette().color(background_role()));
+    painter.translate(frame_thickness(), frame_thickness());
+    painter.translate(-horizontal_scrollbar().value(), -vertical_scrollbar().value());
+
+    // Why we need to translate here again? We've already translated the painter.
+    // Anyways, it paints correctly so I'll leave it like this.
+    painter.fill_rect_with_dither_pattern(
+        separator_rect().translated(horizontal_scrollbar().value(), vertical_scrollbar().value()),
+        Gfx::Color::LightGray,
+        Gfx::Color::White);
+
+    size_t y_offset = 10;
+    size_t current_original_line_index = 0;
+    for (const auto& hunk : m_hunks) {
+        for (size_t i = current_original_line_index; i < hunk.original_start_line; ++i) {
+            draw_line(painter, m_original_lines[i], y_offset, LinePosition::Both, LineType::Normal);
+            y_offset += line_height();
+        }
+        current_original_line_index = hunk.original_start_line + hunk.removed_lines.size();
+
+        size_t left_y_offset = y_offset;
+        for (const auto& removed_line : hunk.removed_lines) {
+            draw_line(painter, removed_line, left_y_offset, LinePosition::Left, LineType::Diff);
+            left_y_offset += line_height();
+        }
+        for (int i = 0; i < (int)hunk.added_lines.size() - (int)hunk.removed_lines.size(); ++i) {
+            draw_line(painter, "", left_y_offset, LinePosition::Left, LineType::Missing);
+            left_y_offset += line_height();
+        }
+
+        size_t right_y_offset = y_offset;
+        for (const auto& added_line : hunk.added_lines) {
+            draw_line(painter, added_line, right_y_offset, LinePosition::Right, LineType::Diff);
+            right_y_offset += line_height();
+        }
+        for (int i = 0; i < (int)hunk.removed_lines.size() - (int)hunk.added_lines.size(); ++i) {
+            draw_line(painter, "", right_y_offset, LinePosition::Right, LineType::Missing);
+            right_y_offset += line_height();
+        }
+
+        ASSERT(left_y_offset == right_y_offset);
+        y_offset = left_y_offset;
+    }
+    for (size_t i = current_original_line_index; i < m_original_lines.size(); ++i) {
+        draw_line(painter, m_original_lines[i], y_offset, LinePosition::Both, LineType::Normal);
+        y_offset += line_height();
+    }
+}
+
+void DiffViewer::draw_line(GUI::Painter& painter, const String& line, size_t y_offset, LinePosition line_position, LineType line_type)
+{
+    size_t line_width = font().width(line);
+
+    constexpr size_t padding = 10;
+    size_t left_side_x_offset = padding;
+    size_t right_side_x_offset = separator_rect().x() + padding;
+
+    // FIXME: Long lines will overflow out of their side of the diff view
+    Gfx::IntRect left_line_rect { (int)left_side_x_offset, (int)y_offset, (int)line_width, (int)line_height() };
+    Gfx::IntRect right_line_rect { (int)right_side_x_offset, (int)y_offset, (int)line_width, (int)line_height() };
+    auto color = palette().color(foreground_role());
+
+    if (line_position == LinePosition::Left || line_position == LinePosition::Both) {
+        painter.draw_text(left_line_rect, line, Gfx::TextAlignment::TopLeft, color);
+        if (line_type != LineType::Normal) {
+            Gfx::IntRect outline = { (int)left_side_x_offset, ((int)y_offset) - 2, separator_rect().x() - (int)(padding * 2), (int)line_height() };
+            if (line_type == LineType::Diff) {
+                painter.fill_rect(
+                    outline,
+                    red_background());
+            }
+            if (line_type == LineType::Missing) {
+                painter.fill_rect(
+                    outline,
+                    gray_background());
+            }
+        }
+    }
+    if (line_position == LinePosition::Right || line_position == LinePosition::Both) {
+        painter.draw_text(right_line_rect, line, Gfx::TextAlignment::TopLeft, color);
+        if (line_type != LineType::Normal) {
+            Gfx::IntRect outline = { (int)right_side_x_offset, ((int)y_offset) - 2, frame_inner_rect().width() - separator_rect().x() - (int)(padding * 2) - 10, (int)line_height() };
+            if (line_type == LineType::Diff) {
+                painter.fill_rect(
+                    outline,
+                    green_background());
+            }
+            if (line_type == LineType::Missing) {
+                painter.fill_rect(
+                    outline,
+                    gray_background());
+            }
+        }
+    }
+}
+
+size_t DiffViewer::line_height() const
+{
+    return font().glyph_height() + 4;
+}
+
+Gfx::IntRect DiffViewer::separator_rect() const
+{
+    return Gfx::IntRect { frame_inner_rect().width() / 2 - 2,
+        0,
+        4,
+        frame_inner_rect().height() };
+}
+
+void DiffViewer::set_content(const String& original, const String& diff)
+{
+    m_original_lines = split_to_lines(original);
+    m_hunks = Diff::parse_hunks(diff);
+
+#ifdef DEBUG_DIFF
+    for (size_t i = 0; i < m_original_lines.size(); ++i)
+        dbgln("{}:{}", i, m_original_lines[i]);
+#endif
+}
+
+DiffViewer::DiffViewer()
+{
+    setup_properties();
+}
+
+DiffViewer::DiffViewer(const String& original, const String& diff)
+    : m_original_lines(split_to_lines(original))
+    , m_hunks(Diff::parse_hunks(diff))
+{
+    setup_properties();
+}
+
+void DiffViewer::setup_properties()
+{
+    set_font(Gfx::FontDatabase::default_fixed_width_font());
+    set_background_role(ColorRole::Base);
+    set_foreground_role(ColorRole::BaseText);
+}
+
+Vector<String> DiffViewer::split_to_lines(const String& text)
+{
+    // NOTE: This is slightly different than text.split('\n')
+    Vector<String> lines;
+    size_t next_line_start_index = 0;
+    for (size_t i = 0; i < text.length(); ++i) {
+        if (text[i] == '\n') {
+            auto line_text = text.substring(next_line_start_index, i - next_line_start_index);
+            lines.append(move(line_text));
+            next_line_start_index = i + 1;
+        }
+    }
+    lines.append(text.substring(next_line_start_index, text.length() - next_line_start_index));
+    return lines;
+}
+
+Gfx::Color DiffViewer::red_background()
+{
+    static Gfx::Color color = Gfx::Color::from_rgba(0x88ff0000);
+    return color;
+}
+
+Gfx::Color DiffViewer::green_background()
+{
+    static Gfx::Color color = Gfx::Color::from_rgba(0x8800ff00);
+    return color;
+}
+
+Gfx::Color DiffViewer::gray_background()
+{
+    static Gfx::Color color = Gfx::Color::from_rgba(0x88888888);
+    return color;
+}
+
+void DiffViewer::update_content_size()
+{
+    if (m_hunks.is_empty()) {
+        set_content_size({ 0, 0 });
+        return;
+    }
+
+    size_t num_lines = 0;
+    size_t current_original_line_index = 0;
+    for (const auto& hunk : m_hunks) {
+        num_lines += ((int)hunk.original_start_line - (int)current_original_line_index);
+
+        num_lines += hunk.removed_lines.size();
+        if (hunk.added_lines.size() > hunk.removed_lines.size()) {
+            num_lines += ((int)hunk.added_lines.size() - (int)hunk.removed_lines.size());
+        }
+        current_original_line_index = hunk.original_start_line + hunk.removed_lines.size();
+    }
+    num_lines += ((int)m_original_lines.size() - (int)current_original_line_index);
+
+    // TODO: Support Horizontal scrolling
+    set_content_size({ 0, (int)(num_lines * line_height()) });
+}
+
+void DiffViewer::resize_event(GUI::ResizeEvent& event)
+{
+    ScrollableWidget::resize_event(event);
+    update_content_size();
+}
+
+}

Userland/DevTools/HackStudio/Git/DiffViewer.h

@@ -0,0 +1,80 @@
+/*
+ * Copyright (c) 2020, Itamar S. <itamar8910@gmail.com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <AK/String.h>
+#include <AK/Vector.h>
+#include <LibDiff/Hunks.h>
+#include <LibGUI/ScrollableWidget.h>
+
+namespace HackStudio {
+class DiffViewer final : public GUI::ScrollableWidget {
+    C_OBJECT(DiffViewer)
+public:
+    virtual ~DiffViewer() override;
+
+    void set_content(const String& original, const String& diff);
+
+private:
+    DiffViewer(const String& original, const String& diff);
+    DiffViewer();
+
+    void setup_properties();
+
+    virtual void paint_event(GUI::PaintEvent&) override;
+    virtual void resize_event(GUI::ResizeEvent&) override;
+
+    void update_content_size();
+
+    enum class LinePosition {
+        Left,
+        Right,
+        Both,
+    };
+
+    enum class LineType {
+        Normal,
+        Diff,
+        Missing,
+    };
+
+    void draw_line(GUI::Painter&, const String& line, size_t y_offset, LinePosition, LineType);
+
+    static Vector<String> split_to_lines(const String& text);
+
+    static Gfx::Color red_background();
+    static Gfx::Color green_background();
+    static Gfx::Color gray_background();
+
+    size_t line_height() const;
+
+    Gfx::IntRect separator_rect() const;
+
+    Vector<String> m_original_lines;
+    Vector<Diff::Hunk> m_hunks;
+};
+}

Userland/DevTools/HackStudio/Git/GitFilesModel.cpp

@@ -0,0 +1,56 @@
+/*
+ * Copyright (c) 2020, Itamar S. <itamar8910@gmail.com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "GitFilesModel.h"
+
+namespace HackStudio {
+
+NonnullRefPtr<GitFilesModel> GitFilesModel::create(Vector<LexicalPath>&& files)
+{
+    return adopt(*new GitFilesModel(move(files)));
+}
+
+GitFilesModel::GitFilesModel(Vector<LexicalPath>&& files)
+    : m_files(move(files))
+{
+}
+
+GUI::Variant GitFilesModel::data(const GUI::ModelIndex& index, GUI::ModelRole role) const
+{
+    if (role == GUI::ModelRole::Display) {
+        return m_files.at(index.row()).string();
+    }
+    return {};
+}
+
+GUI::ModelIndex GitFilesModel::index(int row, int column, const GUI::ModelIndex&) const
+{
+    if (row < 0 || row >= static_cast<int>(m_files.size()))
+        return {};
+    return create_index(row, column, &m_files.at(row));
+}
+
+};

Userland/DevTools/HackStudio/Git/GitFilesModel.h

@@ -0,0 +1,57 @@
+/*
+ * Copyright (c) 2020, Itamar S. <itamar8910@gmail.com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include "GitRepo.h"
+#include <AK/LexicalPath.h>
+#include <AK/NonnullRefPtr.h>
+#include <LibGUI/Model.h>
+
+namespace HackStudio {
+
+class GitFilesModel final : public GUI::Model {
+public:
+    static NonnullRefPtr<GitFilesModel> create(Vector<LexicalPath>&& files);
+
+    virtual int row_count(const GUI::ModelIndex& = GUI::ModelIndex()) const override { return m_files.size(); }
+    virtual int column_count(const GUI::ModelIndex& = GUI::ModelIndex()) const override { return 1; }
+
+    virtual String column_name(int) const override
+    {
+        return "";
+    }
+
+    virtual GUI::Variant data(const GUI::ModelIndex&, GUI::ModelRole) const override;
+
+    virtual void update() override { }
+    virtual GUI::ModelIndex index(int row, int column, const GUI::ModelIndex&) const override;
+
+private:
+    explicit GitFilesModel(Vector<LexicalPath>&& files);
+    Vector<LexicalPath> m_files;
+};
+}

Userland/DevTools/HackStudio/Git/GitFilesView.cpp

@@ -0,0 +1,82 @@
+/*
+ * Copyright (c) 2020, Itamar S. <itamar8910@gmail.com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "GitFilesView.h"
+#include <LibGUI/Model.h>
+#include <LibGUI/Painter.h>
+#include <LibGUI/ScrollBar.h>
+#include <LibGfx/Palette.h>
+
+namespace HackStudio {
+GitFilesView::~GitFilesView()
+{
+}
+
+void GitFilesView::paint_list_item(GUI::Painter& painter, int row_index, int painted_item_index)
+{
+    ListView::paint_list_item(painter, row_index, painted_item_index);
+
+    painter.blit(action_icon_rect((size_t)painted_item_index).top_left(), *m_action_icon, m_action_icon->rect());
+}
+
+Gfx::IntRect GitFilesView::action_icon_rect(size_t painted_item_index)
+{
+    int y = painted_item_index * item_height();
+    return { content_width() - 20, y, m_action_icon->rect().width(), m_action_icon->rect().height() };
+}
+
+GitFilesView::GitFilesView(GitFileActionCallback callback, NonnullRefPtr<Gfx::Bitmap> action_icon)
+    : m_action_callback(move(callback))
+    , m_action_icon(action_icon)
+{
+    set_alternating_row_colors(false);
+}
+
+void GitFilesView::mousedown_event(GUI::MouseEvent& event)
+{
+    if (event.button() != GUI::MouseButton::Left) {
+        ListView::mousedown_event(event);
+        return;
+    }
+
+    if (event.x() < action_icon_rect(0).x() || event.x() > action_icon_rect(0).top_right().x()) {
+        ListView::mousedown_event(event);
+        return;
+    }
+
+    size_t item_index = (event.y() + vertical_scrollbar().value()) / item_height();
+    if (model()->row_count() == 0 || item_index > (size_t)model()->row_count()) {
+        ListView::mousedown_event(event);
+        return;
+    }
+
+    auto data = model()->index(item_index, model_column()).data();
+
+    ASSERT(data.is_string());
+    m_action_callback(LexicalPath(data.to_string()));
+}
+
+};

Userland/DevTools/HackStudio/Git/GitFilesView.h

@@ -0,0 +1,56 @@
+/*
+ * Copyright (c) 2020, Itamar S. <itamar8910@gmail.com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <AK/LexicalPath.h>
+#include <LibGUI/ListView.h>
+#include <LibGfx/Bitmap.h>
+
+namespace HackStudio {
+
+// A "GitFileAction" is either the staging or the unstaging of a file.
+typedef Function<void(const LexicalPath& file)> GitFileActionCallback;
+
+class GitFilesView : public GUI::ListView {
+    C_OBJECT(GitFilesView)
+public:
+    virtual ~GitFilesView() override;
+
+protected:
+    GitFilesView(GitFileActionCallback, NonnullRefPtr<Gfx::Bitmap> action_icon);
+
+private:
+    virtual void paint_list_item(GUI::Painter& painter, int row_index, int painted_item_index);
+
+    virtual void mousedown_event(GUI::MouseEvent&) override;
+    virtual Gfx::IntRect action_icon_rect(size_t painted_item_index);
+
+    GitFileActionCallback m_action_callback;
+    NonnullRefPtr<Gfx::Bitmap> m_action_icon;
+};
+
+}

Userland/DevTools/HackStudio/Git/GitRepo.cpp

@@ -0,0 +1,151 @@
+/*
+ * Copyright (c) 2020, Itamar S. <itamar8910@gmail.com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "GitRepo.h"
+#include <LibCore/Command.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+namespace HackStudio {
+
+GitRepo::CreateResult GitRepo::try_to_create(const LexicalPath& repository_root)
+{
+    if (!git_is_installed()) {
+        return { CreateResult::Type::GitProgramNotFound, nullptr };
+    }
+    if (!git_repo_exists(repository_root)) {
+        return { CreateResult::Type::NoGitRepo, nullptr };
+    }
+
+    return { CreateResult::Type::Success, adopt(*new GitRepo(repository_root)) };
+}
+
+RefPtr<GitRepo> GitRepo::initialize_repository(const LexicalPath& repository_root)
+{
+    auto res = command_wrapper({ "init" }, repository_root);
+    if (res.is_null())
+        return {};
+
+    ASSERT(git_repo_exists(repository_root));
+    return adopt(*new GitRepo(repository_root));
+}
+
+Vector<LexicalPath> GitRepo::unstaged_files() const
+{
+    auto modified = modified_files();
+    auto untracked = untracked_files();
+    modified.append(move(untracked));
+    return modified;
+}
+//
+Vector<LexicalPath> GitRepo::staged_files() const
+{
+    auto raw_result = command({ "diff", "--cached", "--name-only" });
+    if (raw_result.is_null())
+        return {};
+    return parse_files_list(raw_result);
+}
+
+Vector<LexicalPath> GitRepo::modified_files() const
+{
+    auto raw_result = command({ "ls-files", "--modified", "--exclude-standard" });
+    if (raw_result.is_null())
+        return {};
+    return parse_files_list(raw_result);
+}
+
+Vector<LexicalPath> GitRepo::untracked_files() const
+{
+    auto raw_result = command({ "ls-files", "--others", "--exclude-standard" });
+    if (raw_result.is_null())
+        return {};
+    return parse_files_list(raw_result);
+}
+
+Vector<LexicalPath> GitRepo::parse_files_list(const String& raw_result)
+{
+    auto lines = raw_result.split('\n');
+    Vector<LexicalPath> files;
+    for (const auto& line : lines) {
+        files.empend(line);
+    }
+    return files;
+}
+
+String GitRepo::command(const Vector<String>& command_parts) const
+{
+    return command_wrapper(command_parts, m_repository_root);
+}
+
+String GitRepo::command_wrapper(const Vector<String>& command_parts, const LexicalPath& chdir)
+{
+    return Core::command("git", command_parts, chdir);
+}
+
+bool GitRepo::git_is_installed()
+{
+    return !command_wrapper({ "--help" }, LexicalPath("/")).is_null();
+}
+
+bool GitRepo::git_repo_exists(const LexicalPath& repo_root)
+{
+    return !command_wrapper({ "status" }, repo_root).is_null();
+}
+
+bool GitRepo::stage(const LexicalPath& file)
+{
+    return !command({ "add", file.string() }).is_null();
+}
+
+bool GitRepo::unstage(const LexicalPath& file)
+{
+    return !command({ "reset", "HEAD", "--", file.string() }).is_null();
+}
+
+bool GitRepo::commit(const String& message)
+{
+    return !command({ "commit", "-m", message }).is_null();
+}
+
+Optional<String> GitRepo::original_file_content(const LexicalPath& file) const
+{
+    return command({ "show", String::formatted("HEAD:{}", file) });
+}
+
+Optional<String> GitRepo::unstaged_diff(const LexicalPath& file) const
+{
+    return command({ "diff", file.string().characters() });
+}
+
+bool GitRepo::is_tracked(const LexicalPath& file) const
+{
+    auto res = command({ "ls-files", file.string() });
+    if (res.is_null())
+        return false;
+    return !res.is_empty();
+}
+
+}

Userland/DevTools/HackStudio/Git/GitRepo.h

@@ -0,0 +1,81 @@
+/*
+ * Copyright (c) 2020, Itamar S. <itamar8910@gmail.com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <AK/LexicalPath.h>
+#include <AK/Optional.h>
+#include <AK/RefCounted.h>
+#include <AK/RefPtr.h>
+#include <AK/String.h>
+#include <AK/Vector.h>
+
+namespace HackStudio {
+
+class GitRepo final : public RefCounted<GitRepo> {
+public:
+    struct CreateResult {
+        enum class Type {
+            Success,
+            NoGitRepo,
+            GitProgramNotFound,
+        };
+        Type type;
+        RefPtr<GitRepo> repo;
+    };
+
+    static CreateResult try_to_create(const LexicalPath& repository_root);
+    static RefPtr<GitRepo> initialize_repository(const LexicalPath& repository_root);
+
+    Vector<LexicalPath> unstaged_files() const;
+    Vector<LexicalPath> staged_files() const;
+    bool stage(const LexicalPath& file);
+    bool unstage(const LexicalPath& file);
+    bool commit(const String& message);
+    Optional<String> original_file_content(const LexicalPath& file) const;
+    Optional<String> unstaged_diff(const LexicalPath& file) const;
+    bool is_tracked(const LexicalPath& file) const;
+
+private:
+    static String command_wrapper(const Vector<String>& command_parts, const LexicalPath& chdir);
+    static bool git_is_installed();
+    static bool git_repo_exists(const LexicalPath& repo_root);
+    static Vector<LexicalPath> parse_files_list(const String&);
+
+    explicit GitRepo(const LexicalPath& repository_root)
+        : m_repository_root(repository_root)
+    {
+    }
+
+    Vector<LexicalPath> modified_files() const;
+    Vector<LexicalPath> untracked_files() const;
+
+    String command(const Vector<String>& command_parts) const;
+
+    LexicalPath m_repository_root;
+};
+
+}

Userland/DevTools/HackStudio/Git/GitWidget.cpp

@@ -0,0 +1,188 @@
+/*
+ * Copyright (c) 2020, Itamar S. <itamar8910@gmail.com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "GitWidget.h"
+#include "GitFilesModel.h"
+#include <AK/LogStream.h>
+#include <LibCore/File.h>
+#include <LibDiff/Format.h>
+#include <LibGUI/Application.h>
+#include <LibGUI/BoxLayout.h>
+#include <LibGUI/Button.h>
+#include <LibGUI/InputBox.h>
+#include <LibGUI/Label.h>
+#include <LibGUI/MessageBox.h>
+#include <LibGUI/Model.h>
+#include <LibGUI/Painter.h>
+#include <LibGfx/Bitmap.h>
+#include <stdio.h>
+
+namespace HackStudio {
+
+GitWidget::GitWidget(const LexicalPath& repo_root)
+    : m_repo_root(repo_root)
+{
+    set_layout<GUI::HorizontalBoxLayout>();
+
+    auto& unstaged = add<GUI::Widget>();
+    unstaged.set_layout<GUI::VerticalBoxLayout>();
+    auto& unstaged_header = unstaged.add<GUI::Widget>();
+    unstaged_header.set_layout<GUI::HorizontalBoxLayout>();
+
+    auto& refresh_button = unstaged_header.add<GUI::Button>();
+    refresh_button.set_icon(Gfx::Bitmap::load_from_file("/res/icons/16x16/reload.png"));
+    refresh_button.set_fixed_size(16, 16);
+    refresh_button.set_tooltip("refresh");
+    refresh_button.on_click = [this](int) { refresh(); };
+
+    auto& unstaged_label = unstaged_header.add<GUI::Label>();
+    unstaged_label.set_text("Unstaged");
+
+    unstaged_header.set_fixed_height(20);
+    m_unstaged_files = unstaged.add<GitFilesView>(
+        [this](const auto& file) { stage_file(file); },
+        Gfx::Bitmap::load_from_file("/res/icons/16x16/plus.png").release_nonnull());
+    m_unstaged_files->on_selection = [this](const GUI::ModelIndex& index) {
+        const auto& selected = index.data().as_string();
+        show_diff(LexicalPath(selected));
+    };
+
+    auto& staged = add<GUI::Widget>();
+    staged.set_layout<GUI::VerticalBoxLayout>();
+
+    auto& staged_header = staged.add<GUI::Widget>();
+    staged_header.set_layout<GUI::HorizontalBoxLayout>();
+
+    auto& commit_button = staged_header.add<GUI::Button>();
+    commit_button.set_icon(Gfx::Bitmap::load_from_file("/res/icons/16x16/commit.png"));
+    commit_button.set_fixed_size(16, 16);
+    commit_button.set_tooltip("commit");
+    commit_button.on_click = [this](int) { commit(); };
+
+    auto& staged_label = staged_header.add<GUI::Label>();
+    staged_label.set_text("Staged");
+
+    staged_header.set_fixed_height(20);
+    m_staged_files = staged.add<GitFilesView>(
+        [this](const auto& file) { unstage_file(file); },
+        Gfx::Bitmap::load_from_file("/res/icons/16x16/minus.png").release_nonnull());
+}
+
+bool GitWidget::initialize()
+{
+    auto result = GitRepo::try_to_create(m_repo_root);
+    switch (result.type) {
+    case GitRepo::CreateResult::Type::Success:
+        m_git_repo = result.repo;
+        return true;
+    case GitRepo::CreateResult::Type::GitProgramNotFound:
+        GUI::MessageBox::show(window(), "Please install the Git port", "Error", GUI::MessageBox::Type::Error);
+        return false;
+    case GitRepo::CreateResult::Type::NoGitRepo: {
+        auto decision = GUI::MessageBox::show(window(), "Create git repository?", "Git", GUI::MessageBox::Type::Question, GUI::MessageBox::InputType::YesNo);
+        if (decision != GUI::Dialog::ExecResult::ExecYes)
+            return false;
+        m_git_repo = GitRepo::initialize_repository(m_repo_root);
+        return true;
+    }
+    default:
+        ASSERT_NOT_REACHED();
+    }
+}
+
+bool GitWidget::initialize_if_needed()
+{
+    if (initialized())
+        return true;
+
+    return initialize();
+}
+
+void GitWidget::refresh()
+{
+    if (!initialize_if_needed()) {
+        dbgln("GitWidget initialization failed");
+        return;
+    }
+
+    ASSERT(!m_git_repo.is_null());
+
+    m_unstaged_files->set_model(GitFilesModel::create(m_git_repo->unstaged_files()));
+    m_staged_files->set_model(GitFilesModel::create(m_git_repo->staged_files()));
+}
+
+void GitWidget::stage_file(const LexicalPath& file)
+{
+    dbgln("staging: {}", file);
+    bool rc = m_git_repo->stage(file);
+    ASSERT(rc);
+    refresh();
+}
+
+void GitWidget::unstage_file(const LexicalPath& file)
+{
+    dbgln("unstaging: {}", file);
+    bool rc = m_git_repo->unstage(file);
+    ASSERT(rc);
+    refresh();
+}
+
+void GitWidget::commit()
+{
+    String message;
+    auto res = GUI::InputBox::show(message, window(), "Commit message:", "Commit");
+    if (res != GUI::InputBox::ExecOK || message.is_empty())
+        return;
+    dbgln("commit message: {}", message);
+    m_git_repo->commit(message);
+    refresh();
+}
+
+void GitWidget::set_view_diff_callback(ViewDiffCallback callback)
+{
+    m_view_diff_callback = move(callback);
+}
+
+void GitWidget::show_diff(const LexicalPath& file_path)
+{
+    if (!m_git_repo->is_tracked(file_path)) {
+        auto file = Core::File::construct(file_path.string());
+        if (!file->open(Core::IODevice::ReadOnly)) {
+            perror("open");
+            ASSERT_NOT_REACHED();
+        }
+
+        auto content = file->read_all();
+        String content_string((char*)content.data(), content.size());
+        m_view_diff_callback("", Diff::generate_only_additions(content_string));
+        return;
+    }
+    const auto& original_content = m_git_repo->original_file_content(file_path);
+    const auto& diff = m_git_repo->unstaged_diff(file_path);
+    ASSERT(original_content.has_value() && diff.has_value());
+    m_view_diff_callback(original_content.value(), diff.value());
+}
+}

Userland/DevTools/HackStudio/Git/GitWidget.h

@@ -0,0 +1,65 @@
+/*
+ * Copyright (c) 2020, Itamar S. <itamar8910@gmail.com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include "GitFilesView.h"
+#include "GitRepo.h"
+#include <AK/Function.h>
+#include <LibGUI/Forward.h>
+#include <LibGUI/Widget.h>
+
+namespace HackStudio {
+
+typedef Function<void(const String& original_content, const String& diff)> ViewDiffCallback;
+
+class GitWidget final : public GUI::Widget {
+    C_OBJECT(GitWidget)
+public:
+    virtual ~GitWidget() override { }
+
+    void refresh();
+    void set_view_diff_callback(ViewDiffCallback callback);
+    bool initialized() const { return !m_git_repo.is_null(); };
+
+private:
+    explicit GitWidget(const LexicalPath& repo_root);
+
+    bool initialize();
+    bool initialize_if_needed();
+    void stage_file(const LexicalPath&);
+    void unstage_file(const LexicalPath&);
+    void commit();
+    void show_diff(const LexicalPath&);
+
+    LexicalPath m_repo_root;
+    RefPtr<GitFilesView> m_unstaged_files;
+    RefPtr<GitFilesView> m_staged_files;
+    RefPtr<GitRepo> m_git_repo;
+    ViewDiffCallback m_view_diff_callback;
+};
+
+}

Userland/DevTools/HackStudio/HackStudio.h

@@ -0,0 +1,45 @@
+/*
+ * Copyright (c) 2020, the SerenityOS developers.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include "EditorWrapper.h"
+#include "LanguageClients/ServerConnections.h"
+#include "Project.h"
+#include <AK/String.h>
+#include <LibGUI/TextEditor.h>
+
+namespace HackStudio {
+
+GUI::TextEditor& current_editor();
+void open_file(const String&);
+RefPtr<EditorWrapper> current_editor_wrapper();
+void open_file(const String&);
+Project& project();
+String currently_open_file();
+void set_current_editor_wrapper(RefPtr<EditorWrapper>);
+
+}

Userland/DevTools/HackStudio/HackStudioWidget.cpp

@@ -0,0 +1,945 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2020, Itamar S. <itamar8910@gmail.com>
+ * Copyright (c) 2020, the SerenityOS developers
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "HackStudioWidget.h"
+#include "CursorTool.h"
+#include "Debugger/DebugInfoWidget.h"
+#include "Debugger/Debugger.h"
+#include "Debugger/DisassemblyWidget.h"
+#include "Editor.h"
+#include "EditorWrapper.h"
+#include "FindInFilesWidget.h"
+#include "FormEditorWidget.h"
+#include "FormWidget.h"
+#include "Git/DiffViewer.h"
+#include "Git/GitWidget.h"
+#include "HackStudio.h"
+#include "HackStudioWidget.h"
+#include "Locator.h"
+#include "Project.h"
+#include "TerminalWrapper.h"
+#include "WidgetTool.h"
+#include "WidgetTreeModel.h"
+#include <AK/StringBuilder.h>
+#include <LibCore/ArgsParser.h>
+#include <LibCore/Event.h>
+#include <LibCore/EventLoop.h>
+#include <LibCore/File.h>
+#include <LibDebug/DebugSession.h>
+#include <LibGUI/Action.h>
+#include <LibGUI/ActionGroup.h>
+#include <LibGUI/Application.h>
+#include <LibGUI/BoxLayout.h>
+#include <LibGUI/Button.h>
+#include <LibGUI/EditingEngine.h>
+#include <LibGUI/FilePicker.h>
+#include <LibGUI/InputBox.h>
+#include <LibGUI/ItemListModel.h>
+#include <LibGUI/Label.h>
+#include <LibGUI/Menu.h>
+#include <LibGUI/MenuBar.h>
+#include <LibGUI/MessageBox.h>
+#include <LibGUI/RegularEditingEngine.h>
+#include <LibGUI/Splitter.h>
+#include <LibGUI/StackWidget.h>
+#include <LibGUI/TabWidget.h>
+#include <LibGUI/TableView.h>
+#include <LibGUI/TextBox.h>
+#include <LibGUI/TextEditor.h>
+#include <LibGUI/ToolBar.h>
+#include <LibGUI/ToolBarContainer.h>
+#include <LibGUI/TreeView.h>
+#include <LibGUI/VimEditingEngine.h>
+#include <LibGUI/Widget.h>
+#include <LibGUI/Window.h>
+#include <LibGfx/FontDatabase.h>
+#include <LibThread/Lock.h>
+#include <LibThread/Thread.h>
+#include <LibVT/TerminalWidget.h>
+#include <fcntl.h>
+#include <spawn.h>
+#include <stdio.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+namespace HackStudio {
+
+HackStudioWidget::HackStudioWidget(const String& path_to_project)
+{
+    set_fill_with_background_color(true);
+    set_layout<GUI::VerticalBoxLayout>();
+    layout()->set_spacing(2);
+
+    open_project(path_to_project);
+
+    auto& toolbar_container = add<GUI::ToolBarContainer>();
+
+    auto& outer_splitter = add<GUI::HorizontalSplitter>();
+
+    auto& left_hand_splitter = outer_splitter.add<GUI::VerticalSplitter>();
+    left_hand_splitter.set_fixed_width(150);
+    create_project_tree_view(left_hand_splitter);
+    m_project_tree_view_context_menu = create_project_tree_view_context_menu();
+
+    create_open_files_view(left_hand_splitter);
+
+    m_right_hand_splitter = outer_splitter.add<GUI::VerticalSplitter>();
+    m_right_hand_stack = m_right_hand_splitter->add<GUI::StackWidget>();
+
+    // Put a placeholder widget front & center since we don't have a file open yet.
+    m_right_hand_stack->add<GUI::Widget>();
+
+    create_form_editor(*m_right_hand_stack);
+
+    m_diff_viewer = m_right_hand_stack->add<DiffViewer>();
+
+    m_editors_splitter = m_right_hand_stack->add<GUI::VerticalSplitter>();
+    m_editors_splitter->layout()->set_margins({ 0, 3, 0, 0 });
+    add_new_editor(*m_editors_splitter);
+
+    m_switch_to_next_editor = create_switch_to_next_editor_action();
+    m_switch_to_previous_editor = create_switch_to_previous_editor_action();
+
+    m_remove_current_editor_action = create_remove_current_editor_action();
+    m_open_action = create_open_action();
+    m_save_action = create_save_action();
+
+    create_action_tab(*m_right_hand_splitter);
+
+    m_add_editor_action = create_add_editor_action();
+    m_add_terminal_action = create_add_terminal_action();
+    m_remove_current_terminal_action = create_remove_current_terminal_action();
+
+    m_locator = add<Locator>();
+
+    m_terminal_wrapper->on_command_exit = [this] {
+        m_stop_action->set_enabled(false);
+    };
+
+    m_build_action = create_build_action();
+    m_run_action = create_run_action();
+    m_stop_action = create_stop_action();
+    m_debug_action = create_debug_action();
+
+    initialize_debugger();
+
+    create_toolbar(toolbar_container);
+}
+
+void HackStudioWidget::update_actions()
+{
+    auto is_remove_terminal_enabled = [this]() {
+        auto widget = m_action_tab_widget->active_widget();
+        if (!widget)
+            return false;
+        if (StringView { "TerminalWrapper" } != widget->class_name())
+            return false;
+        if (!reinterpret_cast<TerminalWrapper*>(widget)->user_spawned())
+            return false;
+        return true;
+    };
+
+    m_remove_current_editor_action->set_enabled(m_all_editor_wrappers.size() > 1);
+    m_remove_current_terminal_action->set_enabled(is_remove_terminal_enabled());
+}
+
+void HackStudioWidget::on_action_tab_change()
+{
+    update_actions();
+    auto git_widget = m_action_tab_widget->active_widget();
+    if (!git_widget)
+        return;
+    if (StringView { "GitWidget" } != git_widget->class_name())
+        return;
+    reinterpret_cast<GitWidget*>(git_widget)->refresh();
+}
+
+void HackStudioWidget::open_project(const String& root_path)
+{
+    if (chdir(root_path.characters()) < 0) {
+        perror("chdir");
+        exit(1);
+    }
+    m_project = Project::open_with_root_path(root_path);
+    ASSERT(m_project);
+    if (m_project_tree_view) {
+        m_project_tree_view->set_model(m_project->model());
+        m_project_tree_view->toggle_index(m_project_tree_view->model()->index(0, 0));
+        m_project_tree_view->update();
+    }
+    if (Debugger::is_initialized()) {
+        Debugger::the().reset_breakpoints();
+    }
+}
+
+Vector<String> HackStudioWidget::selected_file_names() const
+{
+    Vector<String> files;
+    m_project_tree_view->selection().for_each_index([&](const GUI::ModelIndex& index) {
+        files.append(index.data().as_string());
+    });
+    return files;
+}
+
+void HackStudioWidget::open_file(const String& filename)
+{
+    if (!currently_open_file().is_empty()) {
+        // Since the file is previously open, it should always be in m_open_files.
+        ASSERT(m_open_files.find(currently_open_file()) != m_open_files.end());
+        auto previous_open_project_file = m_open_files.get(currently_open_file()).value();
+
+        // Update the scrollbar values of the previous_open_project_file and save them to m_open_files.
+        previous_open_project_file->vertical_scroll_value(current_editor().vertical_scrollbar().value());
+        previous_open_project_file->horizontal_scroll_value(current_editor().horizontal_scrollbar().value());
+        m_open_files.set(currently_open_file(), previous_open_project_file);
+    }
+
+    RefPtr<ProjectFile> new_project_file = nullptr;
+    if (auto it = m_open_files.find(filename); it != m_open_files.end()) {
+        new_project_file = it->value;
+    } else {
+        new_project_file = m_project->get_file(filename);
+        if (!new_project_file) {
+            new_project_file = ProjectFile::construct_with_name(filename);
+        }
+        m_open_files.set(filename, *new_project_file);
+        m_open_files_vector.append(filename);
+        m_open_files_view->model()->update();
+    }
+
+    current_editor().set_document(const_cast<GUI::TextDocument&>(new_project_file->document()));
+    current_editor().set_mode(GUI::TextEditor::Editable);
+    current_editor().horizontal_scrollbar().set_value(new_project_file->horizontal_scroll_value());
+    current_editor().vertical_scrollbar().set_value(new_project_file->vertical_scroll_value());
+    current_editor().set_editing_engine(make<GUI::RegularEditingEngine>());
+
+    if (filename.ends_with(".frm")) {
+        set_edit_mode(EditMode::Form);
+    } else {
+        set_edit_mode(EditMode::Text);
+    }
+
+    m_currently_open_file = filename;
+
+    String relative_file_path = m_currently_open_file;
+    if (m_currently_open_file.starts_with(m_project->root_path()))
+        relative_file_path = m_currently_open_file.substring(m_project->root_path().length() + 1);
+
+    window()->set_title(String::formatted("{} - {} - Hack Studio", relative_file_path, m_project->name()));
+    m_project_tree_view->update();
+
+    current_editor_wrapper().filename_label().set_text(filename);
+
+    current_editor().set_focus(true);
+}
+
+EditorWrapper& HackStudioWidget::current_editor_wrapper()
+{
+    ASSERT(m_current_editor_wrapper);
+    return *m_current_editor_wrapper;
+}
+
+GUI::TextEditor& HackStudioWidget::current_editor()
+{
+    return current_editor_wrapper().editor();
+}
+
+void HackStudioWidget::set_edit_mode(EditMode mode)
+{
+    if (mode == EditMode::Text) {
+        m_right_hand_stack->set_active_widget(m_editors_splitter);
+    } else if (mode == EditMode::Form) {
+        m_right_hand_stack->set_active_widget(m_form_inner_container);
+    } else if (mode == EditMode::Diff) {
+        m_right_hand_stack->set_active_widget(m_diff_viewer);
+    } else {
+        ASSERT_NOT_REACHED();
+    }
+    m_right_hand_stack->active_widget()->update();
+}
+
+NonnullRefPtr<GUI::Menu> HackStudioWidget::create_project_tree_view_context_menu()
+{
+    m_open_selected_action = create_open_selected_action();
+    m_new_action = create_new_action();
+    m_delete_action = create_delete_action();
+    auto project_tree_view_context_menu = GUI::Menu::construct("Project Files");
+    project_tree_view_context_menu->add_action(*m_open_selected_action);
+    // TODO: Rename, cut, copy, duplicate with new name, show containing folder ...
+    project_tree_view_context_menu->add_separator();
+    project_tree_view_context_menu->add_action(*m_new_action);
+    project_tree_view_context_menu->add_action(*m_delete_action);
+    return project_tree_view_context_menu;
+}
+
+NonnullRefPtr<GUI::Action> HackStudioWidget::create_new_action()
+{
+    return GUI::Action::create("Add new file to project...", { Mod_Ctrl, Key_N }, Gfx::Bitmap::load_from_file("/res/icons/16x16/new.png"), [this](const GUI::Action&) {
+        String filename;
+        if (GUI::InputBox::show(filename, window(), "Enter name of new file:", "Add new file to project") != GUI::InputBox::ExecOK)
+            return;
+        auto file = Core::File::construct(filename);
+        if (!file->open((Core::IODevice::OpenMode)(Core::IODevice::WriteOnly | Core::IODevice::MustBeNew))) {
+            GUI::MessageBox::show(window(), String::formatted("Failed to create '{}'", filename), "Error", GUI::MessageBox::Type::Error);
+            return;
+        }
+        m_project_tree_view->toggle_index(m_project_tree_view->model()->index(0, 0));
+        open_file(filename);
+    });
+}
+
+NonnullRefPtr<GUI::Action> HackStudioWidget::create_open_selected_action()
+{
+
+    auto open_selected_action = GUI::Action::create("Open", [this](const GUI::Action&) {
+        auto files = selected_file_names();
+        for (auto& file : files)
+            open_file(file);
+    });
+    open_selected_action->set_enabled(true);
+    return open_selected_action;
+}
+
+NonnullRefPtr<GUI::Action> HackStudioWidget::create_delete_action()
+{
+    auto delete_action = GUI::CommonActions::make_delete_action([this](const GUI::Action&) {
+        auto files = selected_file_names();
+        if (files.is_empty())
+            return;
+
+        String message;
+        if (files.size() == 1) {
+            message = String::formatted("Really remove {} from disk?", LexicalPath(files[0]).basename());
+        } else {
+            message = String::formatted("Really remove {} files from disk?", files.size());
+        }
+
+        auto result = GUI::MessageBox::show(window(),
+            message,
+            "Confirm deletion",
+            GUI::MessageBox::Type::Warning,
+            GUI::MessageBox::InputType::OKCancel);
+        if (result == GUI::MessageBox::ExecCancel)
+            return;
+
+        for (auto& file : files) {
+            if (1) {
+                // FIXME: Remove `file` from disk
+            } else {
+                GUI::MessageBox::show(window(),
+                    String::formatted("Removing file {} from the project failed.", file),
+                    "Removal failed",
+                    GUI::MessageBox::Type::Error);
+                break;
+            }
+        }
+    });
+    delete_action->set_enabled(false);
+    return delete_action;
+}
+
+void HackStudioWidget::add_new_editor(GUI::Widget& parent)
+{
+    auto wrapper = EditorWrapper::construct();
+    if (m_action_tab_widget) {
+        parent.insert_child_before(wrapper, *m_action_tab_widget);
+    } else {
+        parent.add_child(wrapper);
+    }
+    m_current_editor_wrapper = wrapper;
+    m_all_editor_wrappers.append(wrapper);
+    wrapper->editor().set_focus(true);
+}
+
+NonnullRefPtr<GUI::Action> HackStudioWidget::create_switch_to_next_editor_action()
+{
+    return GUI::Action::create("Switch to next editor", { Mod_Ctrl, Key_E }, [this](auto&) {
+        if (m_all_editor_wrappers.size() <= 1)
+            return;
+        Vector<EditorWrapper*> wrappers;
+        m_editors_splitter->for_each_child_of_type<EditorWrapper>([this, &wrappers](auto& child) {
+            wrappers.append(&child);
+            return IterationDecision::Continue;
+        });
+        for (size_t i = 0; i < wrappers.size(); ++i) {
+            if (m_current_editor_wrapper.ptr() == wrappers[i]) {
+                if (i == wrappers.size() - 1)
+                    wrappers[0]->editor().set_focus(true);
+                else
+                    wrappers[i + 1]->editor().set_focus(true);
+            }
+        }
+    });
+}
+
+NonnullRefPtr<GUI::Action> HackStudioWidget::create_switch_to_previous_editor_action()
+{
+    return GUI::Action::create("Switch to previous editor", { Mod_Ctrl | Mod_Shift, Key_E }, [this](auto&) {
+        if (m_all_editor_wrappers.size() <= 1)
+            return;
+        Vector<EditorWrapper*> wrappers;
+        m_editors_splitter->for_each_child_of_type<EditorWrapper>([this, &wrappers](auto& child) {
+            wrappers.append(&child);
+            return IterationDecision::Continue;
+        });
+        for (int i = wrappers.size() - 1; i >= 0; --i) {
+            if (m_current_editor_wrapper.ptr() == wrappers[i]) {
+                if (i == 0)
+                    wrappers.last()->editor().set_focus(true);
+                else
+                    wrappers[i - 1]->editor().set_focus(true);
+            }
+        }
+    });
+}
+
+NonnullRefPtr<GUI::Action> HackStudioWidget::create_remove_current_editor_action()
+{
+    return GUI::Action::create("Remove current editor", { Mod_Alt | Mod_Shift, Key_E }, [this](auto&) {
+        if (m_all_editor_wrappers.size() <= 1)
+            return;
+        auto wrapper = m_current_editor_wrapper;
+        m_switch_to_next_editor->activate();
+        m_editors_splitter->remove_child(*wrapper);
+        m_all_editor_wrappers.remove_first_matching([&wrapper](auto& entry) { return entry == wrapper.ptr(); });
+        update_actions();
+    });
+}
+
+NonnullRefPtr<GUI::Action> HackStudioWidget::create_open_action()
+{
+    return GUI::Action::create("Open project...", { Mod_Ctrl | Mod_Shift, Key_O }, Gfx::Bitmap::load_from_file("/res/icons/16x16/open.png"), [this](auto&) {
+        auto open_path = GUI::FilePicker::get_open_filepath(window(), "Open project");
+        if (!open_path.has_value())
+            return;
+        open_project(open_path.value());
+        update_actions();
+    });
+}
+
+NonnullRefPtr<GUI::Action> HackStudioWidget::create_save_action()
+{
+    return GUI::Action::create("Save", { Mod_Ctrl, Key_S }, Gfx::Bitmap::load_from_file("/res/icons/16x16/save.png"), [this](auto&) {
+        if (m_currently_open_file.is_empty())
+            return;
+
+        current_editor().write_to_file(m_currently_open_file);
+
+        if (m_git_widget->initialized())
+            m_git_widget->refresh();
+    });
+}
+
+NonnullRefPtr<GUI::Action> HackStudioWidget::create_remove_current_terminal_action()
+{
+    return GUI::Action::create("Remove current Terminal", { Mod_Alt | Mod_Shift, Key_T }, [this](auto&) {
+        auto widget = m_action_tab_widget->active_widget();
+        if (!widget)
+            return;
+        if (!is<TerminalWrapper>(widget))
+            return;
+        auto& terminal = *static_cast<TerminalWrapper*>(widget);
+        if (!terminal.user_spawned())
+            return;
+        m_action_tab_widget->remove_tab(terminal);
+        update_actions();
+    });
+}
+
+NonnullRefPtr<GUI::Action> HackStudioWidget::create_add_editor_action()
+{
+    return GUI::Action::create("Add new editor", { Mod_Ctrl | Mod_Alt, Key_E },
+        Gfx::Bitmap::load_from_file("/res/icons/16x16/app-text-editor.png"),
+        [this](auto&) {
+            add_new_editor(*m_editors_splitter);
+            update_actions();
+        });
+}
+
+NonnullRefPtr<GUI::Action> HackStudioWidget::create_add_terminal_action()
+{
+    return GUI::Action::create("Add new Terminal", { Mod_Ctrl | Mod_Alt, Key_T },
+        Gfx::Bitmap::load_from_file("/res/icons/16x16/app-terminal.png"),
+        [this](auto&) {
+            auto& terminal_wrapper = m_action_tab_widget->add_tab<TerminalWrapper>("Terminal");
+            reveal_action_tab(terminal_wrapper);
+            update_actions();
+            terminal_wrapper.terminal().set_focus(true);
+        });
+}
+
+void HackStudioWidget::reveal_action_tab(GUI::Widget& widget)
+{
+    if (m_action_tab_widget->min_height() < 200)
+        m_action_tab_widget->set_fixed_height(200);
+    m_action_tab_widget->set_active_widget(&widget);
+}
+
+NonnullRefPtr<GUI::Action> HackStudioWidget::create_debug_action()
+{
+    return GUI::Action::create("Debug", Gfx::Bitmap::load_from_file("/res/icons/16x16/debug-run.png"), [this](auto&) {
+        if (!GUI::FilePicker::file_exists(get_project_executable_path())) {
+            GUI::MessageBox::show(window(), String::formatted("Could not find file: {}. (did you build the project?)", get_project_executable_path()), "Error", GUI::MessageBox::Type::Error);
+            return;
+        }
+        if (Debugger::the().session()) {
+            GUI::MessageBox::show(window(), "Debugger is already running", "Error", GUI::MessageBox::Type::Error);
+            return;
+        }
+
+        Debugger::the().set_executable_path(get_project_executable_path());
+        m_debugger_thread = LibThread::Thread::construct(Debugger::start_static);
+        m_debugger_thread->start();
+    });
+}
+
+void HackStudioWidget::initialize_debugger()
+{
+    Debugger::initialize(
+        m_project->root_path(),
+        [this](const PtraceRegisters& regs) {
+            ASSERT(Debugger::the().session());
+            const auto& debug_session = *Debugger::the().session();
+            auto source_position = debug_session.get_source_position(regs.eip);
+            if (!source_position.has_value()) {
+                dbgln("Could not find source position for address: {:p}", regs.eip);
+                return Debugger::HasControlPassedToUser::No;
+            }
+            dbgln("Debugger stopped at source position: {}:{}", source_position.value().file_path, source_position.value().line_number);
+
+            Core::EventLoop::main().post_event(
+                *window(),
+                make<Core::DeferredInvocationEvent>(
+                    [this, source_position, &regs](auto&) {
+                        m_current_editor_in_execution = get_editor_of_file(source_position.value().file_path);
+                        m_current_editor_in_execution->editor().set_execution_position(source_position.value().line_number - 1);
+                        m_debug_info_widget->update_state(*Debugger::the().session(), regs);
+                        m_debug_info_widget->set_debug_actions_enabled(true);
+                        m_disassembly_widget->update_state(*Debugger::the().session(), regs);
+                        HackStudioWidget::reveal_action_tab(*m_debug_info_widget);
+                    }));
+            Core::EventLoop::wake();
+
+            return Debugger::HasControlPassedToUser::Yes;
+        },
+        [this]() {
+            Core::EventLoop::main().post_event(*window(), make<Core::DeferredInvocationEvent>([this](auto&) {
+                m_debug_info_widget->set_debug_actions_enabled(false);
+                if (m_current_editor_in_execution) {
+                    m_current_editor_in_execution->editor().clear_execution_position();
+                }
+            }));
+            Core::EventLoop::wake();
+        },
+        [this]() {
+            Core::EventLoop::main().post_event(*window(), make<Core::DeferredInvocationEvent>([this](auto&) {
+                m_debug_info_widget->program_stopped();
+                m_disassembly_widget->program_stopped();
+                HackStudioWidget::hide_action_tabs();
+                GUI::MessageBox::show(window(), "Program Exited", "Debugger", GUI::MessageBox::Type::Information);
+            }));
+            Core::EventLoop::wake();
+        });
+}
+
+String HackStudioWidget::get_full_path_of_serenity_source(const String& file)
+{
+    auto path_parts = LexicalPath(file).parts();
+    ASSERT(path_parts[0] == "..");
+    path_parts.remove(0);
+    StringBuilder relative_path_builder;
+    relative_path_builder.join("/", path_parts);
+    constexpr char SERENITY_LIBS_PREFIX[] = "/usr/src/serenity";
+    LexicalPath serenity_sources_base(SERENITY_LIBS_PREFIX);
+    return String::formatted("{}/{}", serenity_sources_base, relative_path_builder.to_string());
+}
+
+NonnullRefPtr<EditorWrapper> HackStudioWidget::get_editor_of_file(const String& file_name)
+{
+
+    String file_path = file_name;
+
+    // TODO: We can probably do a more specific condition here, something like
+    // "if (file.starts_with("../Libraries/") || file.starts_with("../AK/"))"
+    if (file_name.starts_with("../")) {
+        file_path = get_full_path_of_serenity_source(file_name);
+    }
+
+    open_file(file_path);
+    return current_editor_wrapper();
+}
+
+String HackStudioWidget::get_project_executable_path() const
+{
+    // FIXME: Dumb heuristic ahead!
+    // e.g /my/project => /my/project/project
+    // TODO: Perhaps a Makefile rule for getting the value of $(PROGRAM) would be better?
+    return String::formatted("{}/{}", m_project->root_path(), LexicalPath(m_project->root_path()).basename());
+}
+
+void HackStudioWidget::build(TerminalWrapper& wrapper)
+{
+    if (m_currently_open_file.ends_with(".js"))
+        wrapper.run_command(String::formatted("js -A {}", m_currently_open_file));
+    else
+        wrapper.run_command("make");
+}
+
+void HackStudioWidget::run(TerminalWrapper& wrapper)
+{
+    if (m_currently_open_file.ends_with(".js"))
+        wrapper.run_command(String::formatted("js {}", m_currently_open_file));
+    else
+        wrapper.run_command("make run");
+}
+
+void HackStudioWidget::hide_action_tabs()
+{
+    m_action_tab_widget->set_fixed_height(24);
+};
+
+Project& HackStudioWidget::project()
+{
+    return *m_project;
+}
+
+void HackStudioWidget::set_current_editor_wrapper(RefPtr<EditorWrapper> editor_wrapper)
+{
+    m_current_editor_wrapper = editor_wrapper;
+}
+
+void HackStudioWidget::create_project_tree_view(GUI::Widget& parent)
+{
+    m_project_tree_view = parent.add<GUI::TreeView>();
+    m_project_tree_view->set_model(m_project->model());
+
+    for (int column_index = 0; column_index < m_project->model().column_count(); ++column_index)
+        m_project_tree_view->set_column_hidden(column_index, true);
+
+    m_project_tree_view->set_column_hidden(GUI::FileSystemModel::Column::Name, false);
+
+    m_project_tree_view->on_context_menu_request = [this](const GUI::ModelIndex& index, const GUI::ContextMenuEvent& event) {
+        if (index.is_valid()) {
+            m_project_tree_view_context_menu->popup(event.screen_position(), m_open_selected_action);
+        }
+    };
+
+    m_project_tree_view->on_selection_change = [this] {
+        m_open_selected_action->set_enabled(!m_project_tree_view->selection().is_empty());
+        m_delete_action->set_enabled(!m_project_tree_view->selection().is_empty());
+    };
+
+    m_project_tree_view->on_activation = [this](auto& index) {
+        auto filename = index.data(GUI::ModelRole::Custom).to_string();
+        open_file(filename);
+    };
+}
+
+void HackStudioWidget::create_open_files_view(GUI::Widget& parent)
+{
+    m_open_files_view = parent.add<GUI::ListView>();
+    auto open_files_model = GUI::ItemListModel<String>::create(m_open_files_vector);
+    m_open_files_view->set_model(open_files_model);
+
+    m_open_files_view->on_activation = [this](auto& index) {
+        open_file(index.data().to_string());
+    };
+}
+
+void HackStudioWidget::create_form_editor(GUI::Widget& parent)
+{
+    m_form_inner_container = parent.add<GUI::Widget>();
+    m_form_inner_container->set_layout<GUI::HorizontalBoxLayout>();
+    auto& form_widgets_toolbar = m_form_inner_container->add<GUI::ToolBar>(Orientation::Vertical, 26);
+    form_widgets_toolbar.set_fixed_width(38);
+
+    GUI::ActionGroup tool_actions;
+    tool_actions.set_exclusive(true);
+
+    auto cursor_tool_action = GUI::Action::create_checkable("Cursor", Gfx::Bitmap::load_from_file("/res/icons/hackstudio/Cursor.png"), [this](auto&) {
+        m_form_editor_widget->set_tool(make<CursorTool>(*m_form_editor_widget));
+    });
+    cursor_tool_action->set_checked(true);
+    tool_actions.add_action(cursor_tool_action);
+
+    form_widgets_toolbar.add_action(cursor_tool_action);
+
+    GUI::WidgetClassRegistration::for_each([&, this](const GUI::WidgetClassRegistration& reg) {
+        constexpr size_t gui_namespace_prefix_length = sizeof("GUI::") - 1;
+        auto icon_path = String::formatted("/res/icons/hackstudio/G{}.png",
+            reg.class_name().substring(gui_namespace_prefix_length, reg.class_name().length() - gui_namespace_prefix_length));
+        if (!Core::File::exists(icon_path))
+            return;
+
+        auto action = GUI::Action::create_checkable(reg.class_name(), Gfx::Bitmap::load_from_file(icon_path), [&reg, this](auto&) {
+            m_form_editor_widget->set_tool(make<WidgetTool>(*m_form_editor_widget, reg));
+            auto widget = reg.construct();
+            m_form_editor_widget->form_widget().add_child(widget);
+            widget->set_relative_rect(30, 30, 30, 30);
+            m_form_editor_widget->model().update();
+        });
+        action->set_checked(false);
+        tool_actions.add_action(action);
+        form_widgets_toolbar.add_action(move(action));
+    });
+
+    auto& form_editor_inner_splitter = m_form_inner_container->add<GUI::HorizontalSplitter>();
+
+    m_form_editor_widget = form_editor_inner_splitter.add<FormEditorWidget>();
+
+    auto& form_editing_pane_container = form_editor_inner_splitter.add<GUI::VerticalSplitter>();
+    form_editing_pane_container.set_fixed_width(190);
+    form_editing_pane_container.set_layout<GUI::VerticalBoxLayout>();
+
+    auto add_properties_pane = [&](auto& text, auto& pane_widget) {
+        auto& wrapper = form_editing_pane_container.add<GUI::Widget>();
+        wrapper.set_layout<GUI::VerticalBoxLayout>();
+        auto& label = wrapper.add<GUI::Label>(text);
+        label.set_fill_with_background_color(true);
+        label.set_text_alignment(Gfx::TextAlignment::CenterLeft);
+        label.set_font(Gfx::FontDatabase::default_bold_font());
+        label.set_fixed_height(16);
+        wrapper.add_child(pane_widget);
+    };
+
+    m_form_widget_tree_view = GUI::TreeView::construct();
+    m_form_widget_tree_view->set_model(m_form_editor_widget->model());
+    m_form_widget_tree_view->on_selection_change = [this] {
+        m_form_editor_widget->selection().disable_hooks();
+        m_form_editor_widget->selection().clear();
+        m_form_widget_tree_view->selection().for_each_index([this](auto& index) {
+            // NOTE: Make sure we don't add the FormWidget itself to the selection,
+            //       since that would allow you to drag-move the FormWidget.
+            if (index.internal_data() != &m_form_editor_widget->form_widget())
+                m_form_editor_widget->selection().add(*(GUI::Widget*)index.internal_data());
+        });
+        m_form_editor_widget->update();
+        m_form_editor_widget->selection().enable_hooks();
+    };
+
+    m_form_editor_widget->selection().on_add = [this](auto& widget) {
+        m_form_widget_tree_view->selection().add(m_form_editor_widget->model().index_for_widget(widget));
+    };
+    m_form_editor_widget->selection().on_remove = [this](auto& widget) {
+        m_form_widget_tree_view->selection().remove(m_form_editor_widget->model().index_for_widget(widget));
+    };
+    m_form_editor_widget->selection().on_clear = [this] {
+        m_form_widget_tree_view->selection().clear();
+    };
+
+    add_properties_pane("Form widget tree:", *m_form_widget_tree_view);
+    add_properties_pane("Widget properties:", *GUI::TableView::construct());
+}
+
+void HackStudioWidget::create_toolbar(GUI::Widget& parent)
+{
+    auto& toolbar = parent.add<GUI::ToolBar>();
+    toolbar.add_action(*m_new_action);
+    toolbar.add_action(*m_save_action);
+    toolbar.add_action(*m_delete_action);
+    toolbar.add_separator();
+
+    toolbar.add_action(GUI::CommonActions::make_cut_action([this](auto&) { current_editor().cut_action().activate(); }));
+    toolbar.add_action(GUI::CommonActions::make_copy_action([this](auto&) { current_editor().copy_action().activate(); }));
+    toolbar.add_action(GUI::CommonActions::make_paste_action([this](auto&) { current_editor().paste_action().activate(); }));
+    toolbar.add_separator();
+    toolbar.add_action(GUI::CommonActions::make_undo_action([this](auto&) { current_editor().undo_action().activate(); }));
+    toolbar.add_action(GUI::CommonActions::make_redo_action([this](auto&) { current_editor().redo_action().activate(); }));
+    toolbar.add_separator();
+
+    toolbar.add_action(*m_build_action);
+    toolbar.add_separator();
+
+    toolbar.add_action(*m_run_action);
+    toolbar.add_action(*m_stop_action);
+    toolbar.add_separator();
+
+    toolbar.add_action(*m_debug_action);
+}
+
+NonnullRefPtr<GUI::Action> HackStudioWidget::create_build_action()
+{
+    return GUI::Action::create("Build", { Mod_Ctrl, Key_B }, Gfx::Bitmap::load_from_file("/res/icons/16x16/build.png"), [this](auto&) {
+        reveal_action_tab(*m_terminal_wrapper);
+        build(*m_terminal_wrapper);
+        m_stop_action->set_enabled(true);
+    });
+}
+
+NonnullRefPtr<GUI::Action> HackStudioWidget::create_run_action()
+{
+    return GUI::Action::create("Run", { Mod_Ctrl, Key_R }, Gfx::Bitmap::load_from_file("/res/icons/16x16/program-run.png"), [this](auto&) {
+        reveal_action_tab(*m_terminal_wrapper);
+        run(*m_terminal_wrapper);
+        m_stop_action->set_enabled(true);
+    });
+}
+
+void HackStudioWidget::create_action_tab(GUI::Widget& parent)
+{
+    m_action_tab_widget = parent.add<GUI::TabWidget>();
+
+    m_action_tab_widget->set_fixed_height(24);
+    m_action_tab_widget->on_change = [this](auto&) {
+        on_action_tab_change();
+
+        static bool first_time = true;
+        if (!first_time)
+            m_action_tab_widget->set_fixed_height(200);
+        first_time = false;
+    };
+
+    m_find_in_files_widget = m_action_tab_widget->add_tab<FindInFilesWidget>("Find in files");
+    m_terminal_wrapper = m_action_tab_widget->add_tab<TerminalWrapper>("Build", false);
+    m_debug_info_widget = m_action_tab_widget->add_tab<DebugInfoWidget>("Debug");
+    m_disassembly_widget = m_action_tab_widget->add_tab<DisassemblyWidget>("Disassembly");
+    m_git_widget = m_action_tab_widget->add_tab<GitWidget>("Git", LexicalPath(m_project->root_path()));
+    m_git_widget->set_view_diff_callback([this](const auto& original_content, const auto& diff) {
+        m_diff_viewer->set_content(original_content, diff);
+        set_edit_mode(EditMode::Diff);
+    });
+}
+
+void HackStudioWidget::create_app_menubar(GUI::MenuBar& menubar)
+{
+    auto& app_menu = menubar.add_menu("Hack Studio");
+    app_menu.add_action(*m_open_action);
+    app_menu.add_action(*m_save_action);
+    app_menu.add_separator();
+    app_menu.add_action(GUI::CommonActions::make_quit_action([](auto&) {
+        GUI::Application::the()->quit();
+    }));
+}
+
+void HackStudioWidget::create_project_menubar(GUI::MenuBar& menubar)
+{
+    auto& project_menu = menubar.add_menu("Project");
+    project_menu.add_action(*m_new_action);
+}
+
+void HackStudioWidget::create_edit_menubar(GUI::MenuBar& menubar)
+{
+    auto& edit_menu = menubar.add_menu("Edit");
+    edit_menu.add_action(GUI::Action::create("Find in files...", { Mod_Ctrl | Mod_Shift, Key_F }, Gfx::Bitmap::load_from_file("/res/icons/16x16/find.png"), [this](auto&) {
+        reveal_action_tab(*m_find_in_files_widget);
+        m_find_in_files_widget->focus_textbox_and_select_all();
+    }));
+
+    edit_menu.add_separator();
+
+    auto line_wrapping_action = GUI::Action::create_checkable("Line wrapping", [this](auto& action) {
+        for (auto& wrapper : m_all_editor_wrappers) {
+            wrapper.editor().set_line_wrapping_enabled(action.is_checked());
+        }
+    });
+    line_wrapping_action->set_checked(current_editor().is_line_wrapping_enabled());
+    edit_menu.add_action(line_wrapping_action);
+
+    edit_menu.add_separator();
+
+    auto vim_emulation_setting_action = GUI::Action::create_checkable("Vim emulation", { Mod_Ctrl | Mod_Shift | Mod_Alt, Key_V }, [this](auto& action) {
+        if (action.is_checked())
+            current_editor().set_editing_engine(make<GUI::VimEditingEngine>());
+        else
+            current_editor().set_editing_engine(make<GUI::RegularEditingEngine>());
+    });
+    vim_emulation_setting_action->set_checked(false);
+    edit_menu.add_action(vim_emulation_setting_action);
+}
+
+void HackStudioWidget::create_build_menubar(GUI::MenuBar& menubar)
+{
+    auto& build_menu = menubar.add_menu("Build");
+    build_menu.add_action(*m_build_action);
+    build_menu.add_separator();
+    build_menu.add_action(*m_run_action);
+    build_menu.add_action(*m_stop_action);
+    build_menu.add_separator();
+    build_menu.add_action(*m_debug_action);
+}
+
+void HackStudioWidget::create_view_menubar(GUI::MenuBar& menubar)
+{
+    auto hide_action_tabs_action = GUI::Action::create("Hide action tabs", { Mod_Ctrl | Mod_Shift, Key_X }, [this](auto&) {
+        hide_action_tabs();
+    });
+    auto open_locator_action = GUI::Action::create("Open locator", { Mod_Ctrl, Key_K }, [this](auto&) {
+        m_locator->open();
+    });
+
+    auto& view_menu = menubar.add_menu("View");
+    view_menu.add_action(hide_action_tabs_action);
+    view_menu.add_action(open_locator_action);
+    view_menu.add_separator();
+    view_menu.add_action(*m_add_editor_action);
+    view_menu.add_action(*m_remove_current_editor_action);
+    view_menu.add_action(*m_add_terminal_action);
+    view_menu.add_action(*m_remove_current_terminal_action);
+}
+
+void HackStudioWidget::create_help_menubar(GUI::MenuBar& menubar)
+{
+    auto& help_menu = menubar.add_menu("Help");
+    help_menu.add_action(GUI::CommonActions::make_about_action("Hack Studio", GUI::Icon::default_icon("app-hack-studio"), window()));
+}
+
+NonnullRefPtr<GUI::Action> HackStudioWidget::create_stop_action()
+{
+    auto action = GUI::Action::create("Stop", Gfx::Bitmap::load_from_file("/res/icons/16x16/program-stop.png"), [this](auto&) {
+        m_terminal_wrapper->kill_running_command();
+    });
+
+    action->set_enabled(false);
+    return action;
+}
+
+void HackStudioWidget::initialize_menubar(GUI::MenuBar& menubar)
+{
+    create_app_menubar(menubar);
+    create_project_menubar(menubar);
+    create_edit_menubar(menubar);
+    create_build_menubar(menubar);
+    create_view_menubar(menubar);
+    create_help_menubar(menubar);
+}
+
+HackStudioWidget::~HackStudioWidget()
+{
+    if (!m_debugger_thread.is_null()) {
+        Debugger::the().set_requested_debugger_action(Debugger::DebuggerAction::Exit);
+        dbgln("Waiting for debugger thread to terminate");
+        auto rc = m_debugger_thread->join();
+        if (rc.is_error()) {
+            warnln("pthread_join: {}", strerror(rc.error().value()));
+            dbgln("error joining debugger thread");
+        }
+    }
+}
+
+}

Userland/DevTools/HackStudio/HackStudioWidget.h

@@ -0,0 +1,170 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2020, Itamar S. <itamar8910@gmail.com>
+ * Copyright (c) 2020, the SerenityOS developers
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include "Debugger/DebugInfoWidget.h"
+#include "Debugger/DisassemblyWidget.h"
+#include "EditorWrapper.h"
+#include "FindInFilesWidget.h"
+#include "FormEditorWidget.h"
+#include "Git/DiffViewer.h"
+#include "Git/GitWidget.h"
+#include "Locator.h"
+#include "Project.h"
+#include "ProjectFile.h"
+#include "TerminalWrapper.h"
+#include <LibGUI/ScrollBar.h>
+#include <LibGUI/Splitter.h>
+#include <LibGUI/Widget.h>
+#include <LibThread/Thread.h>
+
+namespace HackStudio {
+
+class HackStudioWidget : public GUI::Widget {
+    C_OBJECT(HackStudioWidget)
+
+public:
+    virtual ~HackStudioWidget() override;
+    void open_file(const String& filename);
+
+    Vector<String> selected_file_names() const;
+
+    void update_actions();
+    Project& project();
+    GUI::TextEditor& current_editor();
+    EditorWrapper& current_editor_wrapper();
+    void set_current_editor_wrapper(RefPtr<EditorWrapper>);
+
+    String currently_open_file() const { return m_currently_open_file; }
+    void initialize_menubar(GUI::MenuBar&);
+
+private:
+    static String get_full_path_of_serenity_source(const String& file);
+
+    HackStudioWidget(const String& path_to_project);
+    void open_project(const String& root_path);
+
+    enum class EditMode {
+        Text,
+        Form,
+        Diff,
+    };
+
+    void set_edit_mode(EditMode);
+
+    NonnullRefPtr<GUI::Menu> create_project_tree_view_context_menu();
+    NonnullRefPtr<GUI::Action> create_new_action();
+    NonnullRefPtr<GUI::Action> create_open_selected_action();
+    NonnullRefPtr<GUI::Action> create_delete_action();
+    NonnullRefPtr<GUI::Action> create_switch_to_next_editor_action();
+    NonnullRefPtr<GUI::Action> create_switch_to_previous_editor_action();
+    NonnullRefPtr<GUI::Action> create_remove_current_editor_action();
+    NonnullRefPtr<GUI::Action> create_open_action();
+    NonnullRefPtr<GUI::Action> create_save_action();
+    NonnullRefPtr<GUI::Action> create_add_editor_action();
+    NonnullRefPtr<GUI::Action> create_add_terminal_action();
+    NonnullRefPtr<GUI::Action> create_remove_current_terminal_action();
+    NonnullRefPtr<GUI::Action> create_debug_action();
+    NonnullRefPtr<GUI::Action> create_build_action();
+    NonnullRefPtr<GUI::Action> create_run_action();
+    NonnullRefPtr<GUI::Action> create_stop_action();
+
+    void add_new_editor(GUI::Widget& parent);
+    NonnullRefPtr<EditorWrapper> get_editor_of_file(const String& file_name);
+    String get_project_executable_path() const;
+
+    void on_action_tab_change();
+    void reveal_action_tab(GUI::Widget&);
+    void initialize_debugger();
+
+    void create_project_tree_view(GUI::Widget& parent);
+    void create_open_files_view(GUI::Widget& parent);
+    void create_form_editor(GUI::Widget& parent);
+    void create_toolbar(GUI::Widget& parent);
+    void create_action_tab(GUI::Widget& parent);
+    void create_app_menubar(GUI::MenuBar&);
+    void create_project_menubar(GUI::MenuBar&);
+    void create_edit_menubar(GUI::MenuBar&);
+    void create_build_menubar(GUI::MenuBar&);
+    void create_view_menubar(GUI::MenuBar&);
+    void create_help_menubar(GUI::MenuBar&);
+
+    void run(TerminalWrapper& wrapper);
+    void build(TerminalWrapper& wrapper);
+
+    void hide_action_tabs();
+
+    NonnullRefPtrVector<EditorWrapper> m_all_editor_wrappers;
+    RefPtr<EditorWrapper> m_current_editor_wrapper;
+
+    // FIXME: This doesn't seem compatible with multiple split editors
+    String m_currently_open_file;
+
+    HashMap<String, NonnullRefPtr<ProjectFile>> m_open_files;
+    Vector<String> m_open_files_vector; // NOTE: This contains the keys from m_open_files
+
+    OwnPtr<Project> m_project;
+
+    RefPtr<GUI::TreeView> m_project_tree_view;
+    RefPtr<GUI::ListView> m_open_files_view;
+    RefPtr<GUI::VerticalSplitter> m_right_hand_splitter;
+    RefPtr<GUI::StackWidget> m_right_hand_stack;
+    RefPtr<GUI::Splitter> m_editors_splitter;
+    RefPtr<GUI::Widget> m_form_inner_container;
+    RefPtr<FormEditorWidget> m_form_editor_widget;
+    RefPtr<GUI::TreeView> m_form_widget_tree_view;
+    RefPtr<DiffViewer> m_diff_viewer;
+    RefPtr<GitWidget> m_git_widget;
+    RefPtr<GUI::Menu> m_project_tree_view_context_menu;
+    RefPtr<GUI::TabWidget> m_action_tab_widget;
+    RefPtr<TerminalWrapper> m_terminal_wrapper;
+    RefPtr<Locator> m_locator;
+    RefPtr<FindInFilesWidget> m_find_in_files_widget;
+    RefPtr<DebugInfoWidget> m_debug_info_widget;
+    RefPtr<DisassemblyWidget> m_disassembly_widget;
+    RefPtr<LibThread::Thread> m_debugger_thread;
+    RefPtr<EditorWrapper> m_current_editor_in_execution;
+
+    RefPtr<GUI::Action> m_new_action;
+    RefPtr<GUI::Action> m_open_selected_action;
+    RefPtr<GUI::Action> m_delete_action;
+    RefPtr<GUI::Action> m_switch_to_next_editor;
+    RefPtr<GUI::Action> m_switch_to_previous_editor;
+    RefPtr<GUI::Action> m_remove_current_editor_action;
+    RefPtr<GUI::Action> m_open_action;
+    RefPtr<GUI::Action> m_save_action;
+    RefPtr<GUI::Action> m_add_editor_action;
+    RefPtr<GUI::Action> m_add_terminal_action;
+    RefPtr<GUI::Action> m_remove_current_terminal_action;
+    RefPtr<GUI::Action> m_stop_action;
+    RefPtr<GUI::Action> m_debug_action;
+    RefPtr<GUI::Action> m_build_action;
+    RefPtr<GUI::Action> m_run_action;
+};
+}

Userland/DevTools/HackStudio/Language.h

@@ -0,0 +1,38 @@
+/*
+ * Copyright (c) 2020, the SerenityOS developers.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+namespace HackStudio {
+enum class Language {
+    Unknown,
+    Cpp,
+    JavaScript,
+    GML,
+    Ini,
+    Shell,
+};
+}

Userland/DevTools/HackStudio/LanguageClient.cpp

@@ -0,0 +1,72 @@
+/*
+ * Copyright (c) 2020, the SerenityOS developers.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "LanguageClient.h"
+#include <AK/String.h>
+#include <AK/Vector.h>
+
+namespace HackStudio {
+
+void ServerConnection::handle(const Messages::LanguageClient::AutoCompleteSuggestions& message)
+{
+    if (m_language_client)
+        m_language_client->provide_autocomplete_suggestions(message.suggestions());
+}
+
+void LanguageClient::open_file(const String& path, int fd)
+{
+    m_connection.post_message(Messages::LanguageServer::FileOpened(path, fd));
+}
+
+void LanguageClient::set_file_content(const String& path, const String& content)
+{
+    m_connection.post_message(Messages::LanguageServer::SetFileContent(path, content));
+}
+
+void LanguageClient::insert_text(const String& path, const String& text, size_t line, size_t column)
+{
+    m_connection.post_message(Messages::LanguageServer::FileEditInsertText(path, text, line, column));
+}
+
+void LanguageClient::remove_text(const String& path, size_t from_line, size_t from_column, size_t to_line, size_t to_column)
+{
+    m_connection.post_message(Messages::LanguageServer::FileEditRemoveText(path, from_line, from_column, to_line, to_column));
+}
+
+void LanguageClient::request_autocomplete(const String& path, size_t cursor_line, size_t cursor_column)
+{
+    m_connection.post_message(Messages::LanguageServer::AutoCompleteSuggestions(path, cursor_line, cursor_column));
+}
+
+void LanguageClient::provide_autocomplete_suggestions(const Vector<GUI::AutocompleteProvider::Entry>& suggestions)
+{
+    if (on_autocomplete_suggestions)
+        on_autocomplete_suggestions(suggestions);
+
+    // Otherwise, drop it on the floor :shrug:
+}
+
+}

Userland/DevTools/HackStudio/LanguageClient.h

@@ -0,0 +1,122 @@
+/*
+ * Copyright (c) 2020, the SerenityOS developers.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include "AutoCompleteResponse.h"
+#include <AK/Forward.h>
+#include <AK/LexicalPath.h>
+#include <AK/Types.h>
+#include <LibIPC/ServerConnection.h>
+
+#include <DevTools/HackStudio/LanguageServers/LanguageClientEndpoint.h>
+#include <DevTools/HackStudio/LanguageServers/LanguageServerEndpoint.h>
+
+namespace HackStudio {
+
+class LanguageClient;
+
+class ServerConnection
+    : public IPC::ServerConnection<LanguageClientEndpoint, LanguageServerEndpoint>
+    , public LanguageClientEndpoint {
+public:
+    ServerConnection(const StringView& socket)
+        : IPC::ServerConnection<LanguageClientEndpoint, LanguageServerEndpoint>(*this, socket)
+    {
+    }
+
+    void attach(LanguageClient& client)
+    {
+        m_language_client = &client;
+    }
+
+    void detach()
+    {
+        m_language_client = nullptr;
+    }
+
+    virtual void handshake() override
+    {
+        auto response = send_sync<Messages::LanguageServer::Greet>();
+        set_my_client_id(response->client_id());
+    }
+
+    template<typename ConcreteType>
+    static NonnullRefPtr<ServerConnection> get_or_create(const String& project_path)
+    {
+        static HashMap<String, NonnullRefPtr<ConcreteType>> s_instances_for_projects;
+        auto key = LexicalPath { project_path }.string();
+        if (auto instance = s_instances_for_projects.get(key); instance.has_value())
+            return *instance.value();
+
+        auto connection = ConcreteType::construct();
+        connection->handshake();
+        s_instances_for_projects.set(key, *connection);
+        return *connection;
+    }
+
+protected:
+    virtual void handle(const Messages::LanguageClient::AutoCompleteSuggestions&) override;
+
+    LanguageClient* m_language_client { nullptr };
+};
+
+class LanguageClient {
+public:
+    explicit LanguageClient(NonnullRefPtr<ServerConnection>&& connection)
+        : m_connection(*connection)
+        , m_server_connection(move(connection))
+    {
+        m_connection.attach(*this);
+    }
+
+    virtual ~LanguageClient()
+    {
+        m_connection.detach();
+    }
+
+    virtual void open_file(const String& path, int fd);
+    virtual void set_file_content(const String& path, const String& content);
+    virtual void insert_text(const String& path, const String& text, size_t line, size_t column);
+    virtual void remove_text(const String& path, size_t from_line, size_t from_column, size_t to_line, size_t to_column);
+    virtual void request_autocomplete(const String& path, size_t cursor_line, size_t cursor_column);
+
+    void provide_autocomplete_suggestions(const Vector<GUI::AutocompleteProvider::Entry>&);
+
+    Function<void(Vector<GUI::AutocompleteProvider::Entry>)> on_autocomplete_suggestions;
+
+private:
+    ServerConnection& m_connection;
+    NonnullRefPtr<ServerConnection> m_server_connection;
+};
+
+template<typename ServerConnectionT>
+static inline NonnullOwnPtr<LanguageClient> get_language_client(const String& project_path)
+{
+    return make<LanguageClient>(ServerConnection::get_or_create<ServerConnectionT>(project_path));
+}
+
+}

Userland/DevTools/HackStudio/LanguageClients/CMakeLists.txt

@@ -0,0 +1,4 @@
+set(GENERATED_SOURCES
+   ../../LanguageServers/LanguageServerEndpoint.h
+   ../../LanguageServers/LanguageClientEndpoint.h
+)

Userland/DevTools/HackStudio/LanguageClients/ServerConnections.h

@@ -0,0 +1,54 @@
+/*
+ * Copyright (c) 2020, Itamar S. <itamar8910@gmail.com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include "../LanguageClient.h"
+#include <AK/LexicalPath.h>
+#include <DevTools/HackStudio/LanguageServers/LanguageClientEndpoint.h>
+#include <DevTools/HackStudio/LanguageServers/LanguageServerEndpoint.h>
+#include <LibIPC/ServerConnection.h>
+
+#define LANGUAGE_CLIENT(namespace_, socket_name)                                 \
+    namespace namespace_ {                                                       \
+    class ServerConnection : public HackStudio::ServerConnection {               \
+        C_OBJECT(ServerConnection)                                               \
+    private:                                                                     \
+        ServerConnection()                                                       \
+            : HackStudio::ServerConnection("/tmp/portal/language/" #socket_name) \
+        {                                                                        \
+        }                                                                        \
+    };                                                                           \
+    }
+
+namespace LanguageClients {
+
+LANGUAGE_CLIENT(Cpp, cpp)
+LANGUAGE_CLIENT(Shell, shell)
+
+}
+
+#undef LANGUAGE_CLIENT

Userland/DevTools/HackStudio/LanguageServers/CMakeLists.txt

@@ -0,0 +1,5 @@
+compile_ipc(LanguageServer.ipc LanguageServerEndpoint.h)
+compile_ipc(LanguageClient.ipc LanguageClientEndpoint.h)
+
+add_subdirectory(Cpp)
+add_subdirectory(Shell)

Userland/DevTools/HackStudio/LanguageServers/Cpp/AutoComplete.cpp

@@ -0,0 +1,97 @@
+/*
+ * Copyright (c) 2020, Itamar S. <itamar8910@gmail.com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "AutoComplete.h"
+#include <AK/HashTable.h>
+#include <LibCpp/Lexer.h>
+
+// #define DEBUG_AUTOCOMPLETE
+
+namespace LanguageServers::Cpp {
+
+Vector<GUI::AutocompleteProvider::Entry> AutoComplete::get_suggestions(const String& code, const GUI::TextPosition& autocomplete_position)
+{
+    auto lines = code.split('\n', true);
+    Cpp::Lexer lexer(code);
+    auto tokens = lexer.lex();
+
+    auto index_of_target_token = token_in_position(tokens, autocomplete_position);
+    if (!index_of_target_token.has_value())
+        return {};
+
+    auto suggestions = identifier_prefixes(lines, tokens, index_of_target_token.value());
+
+#ifdef DEBUG_AUTOCOMPLETE
+    for (auto& suggestion : suggestions) {
+        dbgln("suggestion: {}", suggestion.completion);
+    }
+#endif
+
+    return suggestions;
+}
+
+StringView AutoComplete::text_of_token(const Vector<String>& lines, const Cpp::Token& token)
+{
+    ASSERT(token.m_start.line == token.m_end.line);
+    ASSERT(token.m_start.column <= token.m_end.column);
+    return lines[token.m_start.line].substring_view(token.m_start.column, token.m_end.column - token.m_start.column + 1);
+}
+
+Optional<size_t> AutoComplete::token_in_position(const Vector<Cpp::Token>& tokens, const GUI::TextPosition& position)
+{
+    for (size_t token_index = 0; token_index < tokens.size(); ++token_index) {
+        auto& token = tokens[token_index];
+        if (token.m_start.line != token.m_end.line)
+            continue;
+        if (token.m_start.line != position.line())
+            continue;
+        if (token.m_start.column + 1 > position.column() || token.m_end.column + 1 < position.column())
+            continue;
+        return token_index;
+    }
+    return {};
+}
+
+Vector<GUI::AutocompleteProvider::Entry> AutoComplete::identifier_prefixes(const Vector<String>& lines, const Vector<Cpp::Token>& tokens, size_t target_token_index)
+{
+    auto partial_input = text_of_token(lines, tokens[target_token_index]);
+    Vector<GUI::AutocompleteProvider::Entry> suggestions;
+
+    HashTable<String> suggestions_lookup; // To avoid duplicate results
+
+    for (size_t i = 0; i < target_token_index; ++i) {
+        auto& token = tokens[i];
+        if (token.m_type != Cpp::Token::Type::Identifier)
+            continue;
+        auto text = text_of_token(lines, token);
+        if (text.starts_with(partial_input) && suggestions_lookup.set(text) == AK::HashSetResult::InsertedNewEntry) {
+            suggestions.append({ text, partial_input.length(), GUI::AutocompleteProvider::CompletionKind::Identifier });
+        }
+    }
+    return suggestions;
+}
+
+}

Userland/DevTools/HackStudio/LanguageServers/Cpp/AutoComplete.h

@@ -0,0 +1,51 @@
+/*
+ * Copyright (c) 2020, Itamar S. <itamar8910@gmail.com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <AK/String.h>
+#include <AK/Vector.h>
+#include <DevTools/HackStudio/AutoCompleteResponse.h>
+#include <LibCpp/Lexer.h>
+#include <LibGUI/TextPosition.h>
+
+namespace LanguageServers::Cpp {
+
+using namespace ::Cpp;
+
+class AutoComplete {
+public:
+    AutoComplete() = delete;
+
+    static Vector<GUI::AutocompleteProvider::Entry> get_suggestions(const String& code, const GUI::TextPosition& autocomplete_position);
+
+private:
+    static Optional<size_t> token_in_position(const Vector<Cpp::Token>&, const GUI::TextPosition&);
+    static StringView text_of_token(const Vector<String>& lines, const Cpp::Token&);
+    static Vector<GUI::AutocompleteProvider::Entry> identifier_prefixes(const Vector<String>& lines, const Vector<Cpp::Token>&, size_t target_token_index);
+};
+
+}

Userland/DevTools/HackStudio/LanguageServers/Cpp/CMakeLists.txt

@@ -0,0 +1,15 @@
+set(SOURCES
+    ClientConnection.cpp
+    main.cpp
+    AutoComplete.cpp
+)
+
+set(GENERATED_SOURCES
+    ../LanguageServerEndpoint.h
+    ../LanguageClientEndpoint.h)
+
+serenity_bin(CppLanguageServer)
+
+# We link with LibGUI because we use GUI::TextDocument to update
+# the content of files according to the edit actions we receive over IPC.
+target_link_libraries(CppLanguageServer LibIPC LibCpp LibGUI)

Userland/DevTools/HackStudio/LanguageServers/Cpp/ClientConnection.cpp

@@ -0,0 +1,177 @@
+/*
+ * Copyright (c) 2020, Itamar S. <itamar8910@gmail.com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "ClientConnection.h"
+#include "AutoComplete.h"
+#include <AK/HashMap.h>
+#include <LibCore/File.h>
+#include <LibGUI/TextDocument.h>
+
+// #define DEBUG_CPP_LANGUAGE_SERVER
+// #define DEBUG_FILE_CONTENT
+
+namespace LanguageServers::Cpp {
+
+static HashMap<int, RefPtr<ClientConnection>> s_connections;
+
+ClientConnection::ClientConnection(NonnullRefPtr<Core::LocalSocket> socket, int client_id)
+    : IPC::ClientConnection<LanguageClientEndpoint, LanguageServerEndpoint>(*this, move(socket), client_id)
+{
+    s_connections.set(client_id, *this);
+}
+
+ClientConnection::~ClientConnection()
+{
+}
+
+void ClientConnection::die()
+{
+    s_connections.remove(client_id());
+    exit(0);
+}
+
+OwnPtr<Messages::LanguageServer::GreetResponse> ClientConnection::handle(const Messages::LanguageServer::Greet&)
+{
+    return make<Messages::LanguageServer::GreetResponse>(client_id());
+}
+
+class DefaultDocumentClient final : public GUI::TextDocument::Client {
+public:
+    virtual ~DefaultDocumentClient() override = default;
+    virtual void document_did_append_line() override {};
+    virtual void document_did_insert_line(size_t) override {};
+    virtual void document_did_remove_line(size_t) override {};
+    virtual void document_did_remove_all_lines() override {};
+    virtual void document_did_change() override {};
+    virtual void document_did_set_text() override {};
+    virtual void document_did_set_cursor(const GUI::TextPosition&) override {};
+
+    virtual bool is_automatic_indentation_enabled() const override { return false; }
+    virtual int soft_tab_width() const override { return 4; }
+};
+
+static DefaultDocumentClient s_default_document_client;
+
+void ClientConnection::handle(const Messages::LanguageServer::FileOpened& message)
+{
+    auto file = Core::File::construct(this);
+    if (!file->open(message.file().fd(), Core::IODevice::ReadOnly, Core::File::ShouldCloseFileDescriptor::Yes)) {
+        errno = file->error();
+        perror("open");
+        dbgln("Failed to open project file");
+        return;
+    }
+    auto content = file->read_all();
+    StringView content_view(content);
+    auto document = GUI::TextDocument::create(&s_default_document_client);
+    document->set_text(content_view);
+    m_open_files.set(message.file_name(), document);
+#ifdef DEBUG_FILE_CONTENT
+    dbg() << document->text();
+#endif
+}
+
+void ClientConnection::handle(const Messages::LanguageServer::FileEditInsertText& message)
+{
+#ifdef DEBUG_CPP_LANGUAGE_SERVER
+    dbgln("InsertText for file: {}", message.file_name());
+    dbgln("Text: {}", message.text());
+    dbgln("[{}:{}]", message.start_line(), message.start_column());
+#endif
+    auto document = document_for(message.file_name());
+    if (!document) {
+        dbgln("file {} has not been opened", message.file_name());
+        return;
+    }
+    GUI::TextPosition start_position { (size_t)message.start_line(), (size_t)message.start_column() };
+    document->insert_at(start_position, message.text(), &s_default_document_client);
+#ifdef DEBUG_FILE_CONTENT
+    dbgln("{}", document->text());
+#endif
+}
+
+void ClientConnection::handle(const Messages::LanguageServer::FileEditRemoveText& message)
+{
+#ifdef DEBUG_CPP_LANGUAGE_SERVER
+    dbgln("RemoveText for file: {}", message.file_name());
+    dbgln("[{}:{} - {}:{}]", message.start_line(), message.start_column(), message.end_line(), message.end_column());
+#endif
+    auto document = document_for(message.file_name());
+    if (!document) {
+        dbgln("file {} has not been opened", message.file_name());
+        return;
+    }
+    GUI::TextPosition start_position { (size_t)message.start_line(), (size_t)message.start_column() };
+    GUI::TextRange range {
+        GUI::TextPosition { (size_t)message.start_line(),
+            (size_t)message.start_column() },
+        GUI::TextPosition { (size_t)message.end_line(),
+            (size_t)message.end_column() }
+    };
+
+    document->remove(range);
+#ifdef DEBUG_FILE_CONTENT
+    dbgln("{}", document->text());
+#endif
+}
+
+void ClientConnection::handle(const Messages::LanguageServer::AutoCompleteSuggestions& message)
+{
+#ifdef DEBUG_CPP_LANGUAGE_SERVER
+    dbgln("AutoCompleteSuggestions for: {} {}:{}", message.file_name(), message.cursor_line(), message.cursor_column());
+#endif
+
+    auto document = document_for(message.file_name());
+    if (!document) {
+        dbgln("file {} has not been opened", message.file_name());
+        return;
+    }
+
+    auto suggestions = AutoComplete::get_suggestions(document->text(), { (size_t)message.cursor_line(), (size_t)max(message.cursor_column(), message.cursor_column() - 1) });
+    post_message(Messages::LanguageClient::AutoCompleteSuggestions(move(suggestions)));
+}
+
+RefPtr<GUI::TextDocument> ClientConnection::document_for(const String& file_name)
+{
+    auto document_optional = m_open_files.get(file_name);
+    if (!document_optional.has_value())
+        return nullptr;
+
+    return document_optional.value();
+}
+
+void ClientConnection::handle(const Messages::LanguageServer::SetFileContent& message)
+{
+    auto document = document_for(message.file_name());
+    if (!document) {
+        dbgln("file {} has not been opened", message.file_name());
+        return;
+    }
+    auto content = message.content();
+    document->set_text(content.view());
+}
+
+}

Userland/DevTools/HackStudio/LanguageServers/Cpp/ClientConnection.h

@@ -0,0 +1,64 @@
+/*
+ * Copyright (c) 2020, Itamar S. <itamar8910@gmail.com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <AK/HashMap.h>
+#include <AK/LexicalPath.h>
+#include <DevTools/HackStudio/AutoCompleteResponse.h>
+#include <LibGUI/TextDocument.h>
+#include <LibIPC/ClientConnection.h>
+
+#include <DevTools/HackStudio/LanguageServers/LanguageClientEndpoint.h>
+#include <DevTools/HackStudio/LanguageServers/LanguageServerEndpoint.h>
+
+namespace LanguageServers::Cpp {
+
+class ClientConnection final
+    : public IPC::ClientConnection<LanguageClientEndpoint, LanguageServerEndpoint>
+    , public LanguageServerEndpoint {
+    C_OBJECT(ClientConnection);
+
+public:
+    explicit ClientConnection(NonnullRefPtr<Core::LocalSocket>, int client_id);
+    ~ClientConnection() override;
+
+    virtual void die() override;
+
+private:
+    virtual OwnPtr<Messages::LanguageServer::GreetResponse> handle(const Messages::LanguageServer::Greet&) override;
+    virtual void handle(const Messages::LanguageServer::FileOpened&) override;
+    virtual void handle(const Messages::LanguageServer::FileEditInsertText&) override;
+    virtual void handle(const Messages::LanguageServer::FileEditRemoveText&) override;
+    virtual void handle(const Messages::LanguageServer::SetFileContent&) override;
+    virtual void handle(const Messages::LanguageServer::AutoCompleteSuggestions&) override;
+
+    RefPtr<GUI::TextDocument> document_for(const String& file_name);
+
+    HashMap<String, NonnullRefPtr<GUI::TextDocument>> m_open_files;
+};
+
+}

Userland/DevTools/HackStudio/LanguageServers/Cpp/main.cpp

@@ -0,0 +1,55 @@
+/*
+ * Copyright (c) 2020, Itamar S. <itamar8910@gmail.com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <AK/LexicalPath.h>
+#include <DevTools/HackStudio/LanguageServers/Cpp/ClientConnection.h>
+#include <LibCore/EventLoop.h>
+#include <LibCore/File.h>
+#include <LibCore/LocalServer.h>
+#include <LibIPC/ClientConnection.h>
+#include <sys/stat.h>
+#include <unistd.h>
+
+int main(int, char**)
+{
+    Core::EventLoop event_loop;
+    if (pledge("stdio unix recvfd", nullptr) < 0) {
+        perror("pledge");
+        return 1;
+    }
+
+    auto socket = Core::LocalSocket::take_over_accepted_socket_from_system_server();
+    IPC::new_client_connection<LanguageServers::Cpp::ClientConnection>(socket.release_nonnull(), 1);
+    if (pledge("stdio recvfd", nullptr) < 0) {
+        perror("pledge");
+        return 1;
+    }
+    if (unveil(nullptr, nullptr) < 0) {
+        perror("unveil");
+        return 1;
+    }
+    return event_loop.exec();
+}

Userland/DevTools/HackStudio/LanguageServers/LanguageClient.ipc

@@ -0,0 +1,4 @@
+endpoint LanguageClient = 8002
+{
+    AutoCompleteSuggestions(Vector<GUI::AutocompleteProvider::Entry> suggestions) =|
+}

Userland/DevTools/HackStudio/LanguageServers/LanguageServer.ipc

@@ -0,0 +1,11 @@
+endpoint LanguageServer = 8001
+{
+    Greet() => (i32 client_id)
+
+    FileOpened(String file_name, IPC::File file) =|
+    FileEditInsertText(String file_name, String text, i32 start_line, i32 start_column) =|
+    FileEditRemoveText(String file_name, i32 start_line, i32 start_column, i32 end_line, i32 end_column) =|
+    SetFileContent(String file_name, String content) =|
+
+    AutoCompleteSuggestions(String file_name, i32 cursor_line, i32 cursor_column) =|
+}

Userland/DevTools/HackStudio/LanguageServers/Shell/AutoComplete.cpp

@@ -0,0 +1,63 @@
+/*
+ * Copyright (c) 2020, the SerenityOS developers.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "AutoComplete.h"
+#include <AK/HashTable.h>
+#include <LibLine/SuggestionManager.h>
+#include <Shell/AST.h>
+#include <Shell/Parser.h>
+#include <Shell/Shell.h>
+
+// #define DEBUG_AUTOCOMPLETE
+
+namespace LanguageServers::Shell {
+
+Vector<GUI::AutocompleteProvider::Entry> AutoComplete::get_suggestions(const String& code, size_t offset)
+{
+    // FIXME: No need to reparse this every time!
+    auto ast = ::Shell::Parser { code }.parse();
+    if (!ast)
+        return {};
+
+#ifdef DEBUG_AUTOCOMPLETE
+    dbgln("Complete '{}'", code);
+    ast->dump(1);
+    dbgln("At offset {}", offset);
+#endif
+
+    auto result = ast->complete_for_editor(m_shell, offset);
+    Vector<GUI::AutocompleteProvider::Entry> completions;
+    for (auto& entry : result) {
+#ifdef DEBUG_AUTOCOMPLETE
+        dbgln("Suggestion: '{}' starting at {}", entry.text_string, entry.input_offset);
+#endif
+        completions.append({ entry.text_string, entry.input_offset });
+    }
+
+    return completions;
+}
+
+}

Userland/DevTools/HackStudio/LanguageServers/Shell/AutoComplete.h

@@ -0,0 +1,50 @@
+/*
+ * Copyright (c) 2020, the SerenityOS developers.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <AK/String.h>
+#include <AK/Vector.h>
+#include <DevTools/HackStudio/AutoCompleteResponse.h>
+#include <LibGUI/TextPosition.h>
+#include <Shell/Shell.h>
+
+namespace LanguageServers::Shell {
+
+class AutoComplete {
+public:
+    AutoComplete()
+        : m_shell(::Shell::Shell::construct())
+    {
+    }
+
+    Vector<GUI::AutocompleteProvider::Entry> get_suggestions(const String& code, size_t autocomplete_position);
+
+private:
+    NonnullRefPtr<::Shell::Shell> m_shell;
+};
+
+}

Userland/DevTools/HackStudio/LanguageServers/Shell/CMakeLists.txt

@@ -0,0 +1,15 @@
+set(SOURCES
+    ClientConnection.cpp
+    main.cpp
+    AutoComplete.cpp
+)
+
+set(GENERATED_SOURCES
+    ../LanguageServerEndpoint.h
+    ../LanguageClientEndpoint.h)
+
+serenity_bin(ShellLanguageServer)
+
+# We link with LibGUI because we use GUI::TextDocument to update
+# the content of files according to the edit actions we receive over IPC.
+target_link_libraries(ShellLanguageServer LibIPC LibShell LibGUI)

Userland/DevTools/HackStudio/LanguageServers/Shell/ClientConnection.cpp

@@ -0,0 +1,186 @@
+/*
+ * Copyright (c) 2020, the SerenityOS developers.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "ClientConnection.h"
+#include "AutoComplete.h"
+#include <AK/HashMap.h>
+#include <LibCore/File.h>
+#include <LibGUI/TextDocument.h>
+
+// #define DEBUG_SH_LANGUAGE_SERVER
+// #define DEBUG_FILE_CONTENT
+
+namespace LanguageServers::Shell {
+
+static HashMap<int, RefPtr<ClientConnection>> s_connections;
+
+ClientConnection::ClientConnection(NonnullRefPtr<Core::LocalSocket> socket, int client_id)
+    : IPC::ClientConnection<LanguageClientEndpoint, LanguageServerEndpoint>(*this, move(socket), client_id)
+{
+    s_connections.set(client_id, *this);
+}
+
+ClientConnection::~ClientConnection()
+{
+}
+
+void ClientConnection::die()
+{
+    s_connections.remove(client_id());
+    exit(0);
+}
+
+OwnPtr<Messages::LanguageServer::GreetResponse> ClientConnection::handle(const Messages::LanguageServer::Greet&)
+{
+    return make<Messages::LanguageServer::GreetResponse>(client_id());
+}
+
+class DefaultDocumentClient final : public GUI::TextDocument::Client {
+public:
+    virtual ~DefaultDocumentClient() override = default;
+    virtual void document_did_append_line() override {};
+    virtual void document_did_insert_line(size_t) override {};
+    virtual void document_did_remove_line(size_t) override {};
+    virtual void document_did_remove_all_lines() override {};
+    virtual void document_did_change() override {};
+    virtual void document_did_set_text() override {};
+    virtual void document_did_set_cursor(const GUI::TextPosition&) override {};
+
+    virtual bool is_automatic_indentation_enabled() const override { return false; }
+    virtual int soft_tab_width() const override { return 4; }
+};
+
+static DefaultDocumentClient s_default_document_client;
+
+void ClientConnection::handle(const Messages::LanguageServer::FileOpened& message)
+{
+    auto file = Core::File::construct(this);
+    if (!file->open(message.file().fd(), Core::IODevice::ReadOnly, Core::File::ShouldCloseFileDescriptor::Yes)) {
+        errno = file->error();
+        perror("open");
+        dbgln("Failed to open project file");
+        return;
+    }
+    auto content = file->read_all();
+    StringView content_view(content);
+    auto document = GUI::TextDocument::create(&s_default_document_client);
+    document->set_text(content_view);
+    m_open_files.set(message.file_name(), document);
+#ifdef DEBUG_FILE_CONTENT
+    dbg() << document->text();
+#endif
+}
+
+void ClientConnection::handle(const Messages::LanguageServer::FileEditInsertText& message)
+{
+#ifdef DEBUG_SH_LANGUAGE_SERVER
+    dbgln("InsertText for file: {}", message.file_name());
+    dbgln("Text: {}", message.text());
+    dbgln("[{}:{}]", message.start_line(), message.start_column());
+#endif
+    auto document = document_for(message.file_name());
+    if (!document) {
+        dbgln("file {} has not been opened", message.file_name());
+        return;
+    }
+    GUI::TextPosition start_position { (size_t)message.start_line(), (size_t)message.start_column() };
+    document->insert_at(start_position, message.text(), &s_default_document_client);
+#ifdef DEBUG_FILE_CONTENT
+    dbgln("{}", document->text());
+#endif
+}
+
+void ClientConnection::handle(const Messages::LanguageServer::FileEditRemoveText& message)
+{
+#ifdef DEBUG_SH_LANGUAGE_SERVER
+    dbgln("RemoveText for file: {}", message.file_name());
+    dbgln("[{}:{} - {}:{}]", message.start_line(), message.start_column(), message.end_line(), message.end_column());
+#endif
+    auto document = document_for(message.file_name());
+    if (!document) {
+        dbgln("file {} has not been opened", message.file_name());
+        return;
+    }
+    GUI::TextPosition start_position { (size_t)message.start_line(), (size_t)message.start_column() };
+    GUI::TextRange range {
+        GUI::TextPosition { (size_t)message.start_line(),
+            (size_t)message.start_column() },
+        GUI::TextPosition { (size_t)message.end_line(),
+            (size_t)message.end_column() }
+    };
+
+    document->remove(range);
+#ifdef DEBUG_FILE_CONTENT
+    dbg() << document->text();
+#endif
+}
+
+void ClientConnection::handle(const Messages::LanguageServer::AutoCompleteSuggestions& message)
+{
+#ifdef DEBUG_SH_LANGUAGE_SERVER
+    dbgln("AutoCompleteSuggestions for: {} {}:{}", message.file_name(), message.cursor_line(), message.cursor_column());
+#endif
+
+    auto document = document_for(message.file_name());
+    if (!document) {
+        dbgln("file {} has not been opened", message.file_name());
+        return;
+    }
+
+    auto& lines = document->lines();
+    size_t offset = 0;
+
+    if (message.cursor_line() > 0) {
+        for (auto i = 0; i < message.cursor_line(); ++i)
+            offset += lines[i].length() + 1;
+    }
+    offset += message.cursor_column();
+
+    auto suggestions = m_autocomplete.get_suggestions(document->text(), offset);
+    post_message(Messages::LanguageClient::AutoCompleteSuggestions(move(suggestions)));
+}
+
+RefPtr<GUI::TextDocument> ClientConnection::document_for(const String& file_name)
+{
+    auto document_optional = m_open_files.get(file_name);
+    if (!document_optional.has_value())
+        return nullptr;
+
+    return document_optional.value();
+}
+
+void ClientConnection::handle(const Messages::LanguageServer::SetFileContent& message)
+{
+    auto document = document_for(message.file_name());
+    if (!document) {
+        dbgln("file {} has not been opened", message.file_name());
+        return;
+    }
+    auto content = message.content();
+    document->set_text(content.view());
+}
+
+}

Userland/DevTools/HackStudio/LanguageServers/Shell/ClientConnection.h

@@ -0,0 +1,67 @@
+/*
+ * Copyright (c) 2020, the SerenityOS developers.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include "AutoComplete.h"
+#include <AK/HashMap.h>
+#include <AK/LexicalPath.h>
+#include <DevTools/HackStudio/AutoCompleteResponse.h>
+#include <LibGUI/TextDocument.h>
+#include <LibIPC/ClientConnection.h>
+
+#include <DevTools/HackStudio/LanguageServers/LanguageClientEndpoint.h>
+#include <DevTools/HackStudio/LanguageServers/LanguageServerEndpoint.h>
+
+namespace LanguageServers::Shell {
+
+class ClientConnection final
+    : public IPC::ClientConnection<LanguageClientEndpoint, LanguageServerEndpoint>
+    , public LanguageServerEndpoint {
+    C_OBJECT(ClientConnection);
+
+public:
+    explicit ClientConnection(NonnullRefPtr<Core::LocalSocket>, int client_id);
+    ~ClientConnection() override;
+
+    virtual void die() override;
+
+private:
+    virtual OwnPtr<Messages::LanguageServer::GreetResponse> handle(const Messages::LanguageServer::Greet&) override;
+    virtual void handle(const Messages::LanguageServer::FileOpened&) override;
+    virtual void handle(const Messages::LanguageServer::FileEditInsertText&) override;
+    virtual void handle(const Messages::LanguageServer::FileEditRemoveText&) override;
+    virtual void handle(const Messages::LanguageServer::SetFileContent&) override;
+    virtual void handle(const Messages::LanguageServer::AutoCompleteSuggestions&) override;
+
+    RefPtr<GUI::TextDocument> document_for(const String& file_name);
+
+    HashMap<String, NonnullRefPtr<GUI::TextDocument>> m_open_files;
+
+    AutoComplete m_autocomplete;
+};
+
+}

Userland/DevTools/HackStudio/LanguageServers/Shell/main.cpp

@@ -0,0 +1,63 @@
+/*
+ * Copyright (c) 2020, the SerenityOS developers.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <AK/LexicalPath.h>
+#include <DevTools/HackStudio/LanguageServers/Shell/ClientConnection.h>
+#include <LibCore/EventLoop.h>
+#include <LibCore/File.h>
+#include <LibCore/LocalServer.h>
+#include <LibIPC/ClientConnection.h>
+#include <sys/stat.h>
+#include <unistd.h>
+
+int main(int, char**)
+{
+    Core::EventLoop event_loop;
+    if (pledge("stdio unix rpath recvfd", nullptr) < 0) {
+        perror("pledge");
+        return 1;
+    }
+
+    auto socket = Core::LocalSocket::take_over_accepted_socket_from_system_server();
+    IPC::new_client_connection<LanguageServers::Shell::ClientConnection>(socket.release_nonnull(), 1);
+    if (pledge("stdio rpath recvfd", nullptr) < 0) {
+        perror("pledge");
+        return 1;
+    }
+    if (unveil("/etc/passwd", "r") < 0) {
+        perror("unveil");
+        return 1;
+    }
+    if (unveil("/", "b") < 0) {
+        perror("unveil");
+        return 1;
+    }
+    if (unveil(nullptr, nullptr) < 0) {
+        perror("unveil");
+        return 1;
+    }
+    return event_loop.exec();
+}

Userland/DevTools/HackStudio/Locator.cpp

@@ -0,0 +1,178 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "Locator.h"
+#include "HackStudio.h"
+#include "Project.h"
+#include <LibGUI/BoxLayout.h>
+#include <LibGUI/FileIconProvider.h>
+#include <LibGUI/TableView.h>
+#include <LibGUI/TextBox.h>
+#include <LibGUI/Window.h>
+
+namespace HackStudio {
+
+class LocatorSuggestionModel final : public GUI::Model {
+public:
+    explicit LocatorSuggestionModel(Vector<String>&& suggestions)
+        : m_suggestions(move(suggestions))
+    {
+    }
+
+    enum Column {
+        Icon,
+        Name,
+        __Column_Count,
+    };
+    virtual int row_count(const GUI::ModelIndex& = GUI::ModelIndex()) const override { return m_suggestions.size(); }
+    virtual int column_count(const GUI::ModelIndex& = GUI::ModelIndex()) const override { return Column::__Column_Count; }
+    virtual GUI::Variant data(const GUI::ModelIndex& index, GUI::ModelRole role) const override
+    {
+        auto& suggestion = m_suggestions.at(index.row());
+        if (role == GUI::ModelRole::Display) {
+            if (index.column() == Column::Name)
+                return suggestion;
+            if (index.column() == Column::Icon)
+                return GUI::FileIconProvider::icon_for_path(suggestion);
+        }
+        return {};
+    }
+    virtual void update() override {};
+
+private:
+    Vector<String> m_suggestions;
+};
+
+Locator::Locator()
+{
+    set_layout<GUI::VerticalBoxLayout>();
+    set_fixed_height(20);
+    m_textbox = add<GUI::TextBox>();
+    m_textbox->on_change = [this] {
+        update_suggestions();
+    };
+    m_textbox->on_escape_pressed = [this] {
+        m_popup_window->hide();
+    };
+    m_textbox->on_up_pressed = [this] {
+        GUI::ModelIndex new_index = m_suggestion_view->selection().first();
+        if (new_index.is_valid())
+            new_index = m_suggestion_view->model()->index(new_index.row() - 1);
+        else
+            new_index = m_suggestion_view->model()->index(0);
+
+        if (m_suggestion_view->model()->is_valid(new_index)) {
+            m_suggestion_view->selection().set(new_index);
+            m_suggestion_view->scroll_into_view(new_index, Orientation::Vertical);
+        }
+    };
+    m_textbox->on_down_pressed = [this] {
+        GUI::ModelIndex new_index = m_suggestion_view->selection().first();
+        if (new_index.is_valid())
+            new_index = m_suggestion_view->model()->index(new_index.row() + 1);
+        else
+            new_index = m_suggestion_view->model()->index(0);
+
+        if (m_suggestion_view->model()->is_valid(new_index)) {
+            m_suggestion_view->selection().set(new_index);
+            m_suggestion_view->scroll_into_view(new_index, Orientation::Vertical);
+        }
+    };
+
+    m_textbox->on_return_pressed = [this] {
+        auto selected_index = m_suggestion_view->selection().first();
+        if (!selected_index.is_valid())
+            return;
+        open_suggestion(selected_index);
+    };
+
+    m_popup_window = GUI::Window::construct();
+    // FIXME: This is obviously not a tooltip window, but it's the closest thing to what we want atm.
+    m_popup_window->set_window_type(GUI::WindowType::Tooltip);
+    m_popup_window->set_rect(0, 0, 500, 200);
+
+    m_suggestion_view = m_popup_window->set_main_widget<GUI::TableView>();
+    m_suggestion_view->set_column_headers_visible(false);
+
+    m_suggestion_view->on_activation = [this](auto& index) {
+        open_suggestion(index);
+    };
+}
+
+Locator::~Locator()
+{
+}
+
+void Locator::open_suggestion(const GUI::ModelIndex& index)
+{
+    auto filename_index = m_suggestion_view->model()->index(index.row(), LocatorSuggestionModel::Column::Name);
+    auto filename = filename_index.data().to_string();
+    open_file(filename);
+    close();
+}
+
+void Locator::open()
+{
+    m_textbox->set_focus(true);
+    if (!m_textbox->text().is_empty()) {
+        m_textbox->select_all();
+        m_popup_window->show();
+    }
+}
+
+void Locator::close()
+{
+    m_popup_window->hide();
+}
+
+void Locator::update_suggestions()
+{
+    auto typed_text = m_textbox->text();
+    Vector<String> suggestions;
+    project().for_each_text_file([&](auto& file) {
+        if (file.name().contains(typed_text, CaseSensitivity::CaseInsensitive))
+            suggestions.append(file.name());
+    });
+    dbgln("I have {} suggestion(s):", suggestions.size());
+    for (auto& s : suggestions) {
+        dbgln("    {}", s);
+    }
+
+    bool has_suggestions = !suggestions.is_empty();
+
+    m_suggestion_view->set_model(adopt(*new LocatorSuggestionModel(move(suggestions))));
+
+    if (!has_suggestions)
+        m_suggestion_view->selection().clear();
+    else
+        m_suggestion_view->selection().set(m_suggestion_view->model()->index(0));
+
+    m_popup_window->move_to(screen_relative_rect().top_left().translated(0, -m_popup_window->height()));
+    dbgln("Popup rect: {}", m_popup_window->rect());
+    m_popup_window->show();
+}
+
+}

Userland/DevTools/HackStudio/Locator.h

@@ -0,0 +1,52 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <LibGUI/Widget.h>
+
+namespace HackStudio {
+
+class Locator final : public GUI::Widget {
+    C_OBJECT(Locator)
+public:
+    virtual ~Locator() override;
+
+    void open();
+    void close();
+
+private:
+    void update_suggestions();
+    void open_suggestion(const GUI::ModelIndex&);
+
+    Locator();
+
+    RefPtr<GUI::TextBox> m_textbox;
+    RefPtr<GUI::Window> m_popup_window;
+    RefPtr<GUI::TableView> m_suggestion_view;
+};
+
+}

Userland/DevTools/HackStudio/Project.cpp

@@ -0,0 +1,84 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "Project.h"
+#include "HackStudio.h"
+#include <LibCore/File.h>
+
+namespace HackStudio {
+
+Project::Project(const String& root_path)
+    : m_root_path(root_path)
+{
+    m_model = GUI::FileSystemModel::create(root_path, GUI::FileSystemModel::Mode::FilesAndDirectories);
+}
+
+Project::~Project()
+{
+}
+
+OwnPtr<Project> Project::open_with_root_path(const String& root_path)
+{
+    if (!Core::File::is_directory(root_path))
+        return {};
+    return adopt_own(*new Project(root_path));
+}
+
+template<typename Callback>
+static void traverse_model(const GUI::FileSystemModel& model, const GUI::ModelIndex& index, Callback callback)
+{
+    if (index.is_valid())
+        callback(index);
+    auto row_count = model.row_count(index);
+    if (!row_count)
+        return;
+    for (int row = 0; row < row_count; ++row) {
+        auto child_index = model.index(row, GUI::FileSystemModel::Column::Name, index);
+        traverse_model(model, child_index, callback);
+    }
+}
+
+void Project::for_each_text_file(Function<void(const ProjectFile&)> callback) const
+{
+    traverse_model(model(), {}, [&](auto& index) {
+        auto file = get_file(model().full_path(index));
+        if (file)
+            callback(*file);
+    });
+}
+
+RefPtr<ProjectFile> Project::get_file(const String& path) const
+{
+    for (auto& file : m_files) {
+        if (file.name() == path)
+            return file;
+    }
+    auto file = ProjectFile::construct_with_name(path);
+    m_files.append(file);
+    return file;
+}
+
+}

Userland/DevTools/HackStudio/Project.h

@@ -0,0 +1,64 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include "ProjectFile.h"
+#include <AK/LexicalPath.h>
+#include <AK/Noncopyable.h>
+#include <AK/OwnPtr.h>
+#include <LibGUI/FileSystemModel.h>
+
+namespace HackStudio {
+
+class Project {
+    AK_MAKE_NONCOPYABLE(Project);
+    AK_MAKE_NONMOVABLE(Project);
+
+public:
+    ~Project();
+
+    static OwnPtr<Project> open_with_root_path(const String& root_path);
+
+    GUI::FileSystemModel& model() { return *m_model; }
+    const GUI::FileSystemModel& model() const { return *m_model; }
+    String name() const { return LexicalPath(m_root_path).basename(); }
+    String root_path() const { return m_root_path; }
+
+    RefPtr<ProjectFile> get_file(const String& path) const;
+
+    void for_each_text_file(Function<void(const ProjectFile&)>) const;
+
+private:
+    explicit Project(const String& root_path);
+
+    RefPtr<GUI::FileSystemModel> m_model;
+    mutable NonnullRefPtrVector<ProjectFile> m_files;
+
+    String m_root_path;
+};
+
+}

Userland/DevTools/HackStudio/ProjectFile.cpp

@@ -0,0 +1,74 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "ProjectFile.h"
+#include <LibCore/File.h>
+#include <string.h>
+
+namespace HackStudio {
+
+ProjectFile::ProjectFile(const String& name)
+    : m_name(name)
+{
+}
+
+GUI::TextDocument& ProjectFile::document() const
+{
+    if (!m_document) {
+        m_document = CodeDocument::create(m_name);
+        auto file_or_error = Core::File::open(m_name, Core::File::ReadOnly);
+        if (file_or_error.is_error()) {
+            warnln("Couldn't open '{}': {}", m_name, file_or_error.error());
+            // This is okay though, we'll just go with an empty document and create the file when saving.
+        } else {
+            auto& file = *file_or_error.value();
+            m_document->set_text(file.read_all());
+        }
+    }
+    return *m_document;
+}
+
+int ProjectFile::vertical_scroll_value() const
+{
+    return m_vertical_scroll_value;
+}
+
+void ProjectFile::vertical_scroll_value(int vertical_scroll_value)
+{
+    m_vertical_scroll_value = vertical_scroll_value;
+}
+
+int ProjectFile::horizontal_scroll_value() const
+{
+    return m_horizontal_scroll_value;
+}
+
+void ProjectFile::horizontal_scroll_value(int horizontal_scroll_value)
+{
+    m_horizontal_scroll_value = horizontal_scroll_value;
+}
+
+}

Userland/DevTools/HackStudio/ProjectFile.h

@@ -0,0 +1,62 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include "CodeDocument.h"
+#include <AK/ByteBuffer.h>
+#include <AK/NonnullRefPtr.h>
+#include <AK/RefCounted.h>
+#include <AK/String.h>
+
+namespace HackStudio {
+
+class ProjectFile : public RefCounted<ProjectFile> {
+public:
+    static NonnullRefPtr<ProjectFile> construct_with_name(const String& name)
+    {
+        return adopt(*new ProjectFile(name));
+    }
+
+    const String& name() const { return m_name; }
+
+    GUI::TextDocument& document() const;
+
+    int vertical_scroll_value() const;
+    void vertical_scroll_value(int);
+    int horizontal_scroll_value() const;
+    void horizontal_scroll_value(int);
+
+private:
+    explicit ProjectFile(const String& name);
+
+    String m_name;
+    mutable RefPtr<CodeDocument> m_document;
+    int m_vertical_scroll_value { 0 };
+    int m_horizontal_scroll_value { 0 };
+};
+
+}

Userland/DevTools/HackStudio/TerminalWrapper.cpp

@@ -0,0 +1,186 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "TerminalWrapper.h"
+#include <AK/String.h>
+#include <LibCore/ConfigFile.h>
+#include <LibGUI/BoxLayout.h>
+#include <LibGUI/MessageBox.h>
+#include <LibVT/TerminalWidget.h>
+#include <fcntl.h>
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/ioctl.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+namespace HackStudio {
+
+void TerminalWrapper::run_command(const String& command)
+{
+    if (m_pid != -1) {
+        GUI::MessageBox::show(window(),
+            "A command is already running in this TerminalWrapper",
+            "Can't run command",
+            GUI::MessageBox::Type::Error);
+        return;
+    }
+
+    int ptm_fd = posix_openpt(O_RDWR | O_CLOEXEC);
+    if (ptm_fd < 0) {
+        perror("posix_openpt");
+        ASSERT_NOT_REACHED();
+    }
+    if (grantpt(ptm_fd) < 0) {
+        perror("grantpt");
+        ASSERT_NOT_REACHED();
+    }
+    if (unlockpt(ptm_fd) < 0) {
+        perror("unlockpt");
+        ASSERT_NOT_REACHED();
+    }
+
+    m_terminal_widget->set_pty_master_fd(ptm_fd);
+    m_terminal_widget->on_command_exit = [this] {
+        int wstatus;
+        int rc = waitpid(m_pid, &wstatus, 0);
+        if (rc < 0) {
+            perror("waitpid");
+            ASSERT_NOT_REACHED();
+        }
+        if (WIFEXITED(wstatus)) {
+            m_terminal_widget->inject_string(String::formatted("\033[{};1m(Command exited with code {})\033[0m\n", wstatus == 0 ? 32 : 31, WEXITSTATUS(wstatus)));
+        } else if (WIFSTOPPED(wstatus)) {
+            m_terminal_widget->inject_string("\033[34;1m(Command stopped!)\033[0m\n");
+        } else if (WIFSIGNALED(wstatus)) {
+            m_terminal_widget->inject_string(String::formatted("\033[34;1m(Command signaled with {}!)\033[0m\n", strsignal(WTERMSIG(wstatus))));
+        }
+        m_pid = -1;
+
+        if (on_command_exit)
+            on_command_exit();
+    };
+
+    m_pid = fork();
+    if (m_pid == 0) {
+        // Create a new process group.
+        setsid();
+
+        const char* tty_name = ptsname(ptm_fd);
+        if (!tty_name) {
+            perror("ptsname");
+            exit(1);
+        }
+        close(ptm_fd);
+        int pts_fd = open(tty_name, O_RDWR);
+        if (pts_fd < 0) {
+            perror("open");
+            exit(1);
+        }
+
+        tcsetpgrp(pts_fd, getpid());
+
+        // NOTE: It's okay if this fails.
+        int rc = ioctl(0, TIOCNOTTY);
+
+        close(0);
+        close(1);
+        close(2);
+
+        rc = dup2(pts_fd, 0);
+        if (rc < 0) {
+            perror("dup2");
+            exit(1);
+        }
+        rc = dup2(pts_fd, 1);
+        if (rc < 0) {
+            perror("dup2");
+            exit(1);
+        }
+        rc = dup2(pts_fd, 2);
+        if (rc < 0) {
+            perror("dup2");
+            exit(1);
+        }
+        rc = close(pts_fd);
+        if (rc < 0) {
+            perror("close");
+            exit(1);
+        }
+        rc = ioctl(0, TIOCSCTTY);
+        if (rc < 0) {
+            perror("ioctl(TIOCSCTTY)");
+            exit(1);
+        }
+
+        setenv("TERM", "xterm", true);
+
+        auto parts = command.split(' ');
+        ASSERT(!parts.is_empty());
+        const char** args = (const char**)calloc(parts.size() + 1, sizeof(const char*));
+        for (size_t i = 0; i < parts.size(); i++) {
+            args[i] = parts[i].characters();
+        }
+        rc = execvp(args[0], const_cast<char**>(args));
+        if (rc < 0) {
+            perror("execve");
+            exit(1);
+        }
+        ASSERT_NOT_REACHED();
+    }
+
+    // (In parent process)
+    terminal().scroll_to_bottom();
+}
+
+void TerminalWrapper::kill_running_command()
+{
+    ASSERT(m_pid != -1);
+
+    // Kill our child process and its whole process group.
+    [[maybe_unused]] auto rc = killpg(m_pid, SIGTERM);
+}
+
+TerminalWrapper::TerminalWrapper(bool user_spawned)
+    : m_user_spawned(user_spawned)
+{
+    set_layout<GUI::VerticalBoxLayout>();
+
+    RefPtr<Core::ConfigFile> config = Core::ConfigFile::get_for_app("Terminal");
+    m_terminal_widget = add<TerminalWidget>(-1, false, config);
+
+    if (user_spawned)
+        run_command("Shell");
+}
+
+TerminalWrapper::~TerminalWrapper()
+{
+}
+
+}

Userland/DevTools/HackStudio/TerminalWrapper.h

@@ -0,0 +1,56 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <LibGUI/Widget.h>
+
+class TerminalWidget;
+
+namespace HackStudio {
+
+class TerminalWrapper final : public GUI::Widget {
+    C_OBJECT(TerminalWrapper)
+public:
+    virtual ~TerminalWrapper() override;
+
+    void run_command(const String&);
+    void kill_running_command();
+
+    bool user_spawned() const { return m_user_spawned; }
+    TerminalWidget& terminal() { return *m_terminal_widget; }
+
+    Function<void()> on_command_exit;
+
+private:
+    explicit TerminalWrapper(bool user_spawned = true);
+
+    RefPtr<TerminalWidget> m_terminal_widget;
+    pid_t m_pid { -1 };
+    bool m_user_spawned { true };
+};
+
+}

Userland/DevTools/HackStudio/Tool.h

@@ -0,0 +1,63 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <AK/Noncopyable.h>
+#include <LibGUI/Forward.h>
+
+namespace HackStudio {
+
+class FormEditorWidget;
+
+class Tool {
+    AK_MAKE_NONCOPYABLE(Tool);
+    AK_MAKE_NONMOVABLE(Tool);
+
+public:
+    virtual ~Tool() { }
+
+    virtual void on_mousedown(GUI::MouseEvent&) = 0;
+    virtual void on_mouseup(GUI::MouseEvent&) = 0;
+    virtual void on_mousemove(GUI::MouseEvent&) = 0;
+    virtual void on_keydown(GUI::KeyEvent&) = 0;
+    virtual void on_second_paint(GUI::Painter&, GUI::PaintEvent&) { }
+
+    virtual const char* class_name() const = 0;
+
+    virtual void attach() { }
+    virtual void detach() { }
+
+protected:
+    explicit Tool(FormEditorWidget& editor)
+        : m_editor(editor)
+    {
+    }
+
+    FormEditorWidget& m_editor;
+};
+
+}

Userland/DevTools/HackStudio/WidgetTool.cpp

@@ -0,0 +1,52 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "WidgetTool.h"
+#include <AK/LogStream.h>
+
+namespace HackStudio {
+
+void WidgetTool::on_mousedown([[maybe_unused]] GUI::MouseEvent& event)
+{
+    dbgln("WidgetTool::on_mousedown");
+}
+
+void WidgetTool::on_mouseup([[maybe_unused]] GUI::MouseEvent& event)
+{
+    dbgln("WidgetTool::on_mouseup");
+}
+
+void WidgetTool::on_mousemove([[maybe_unused]] GUI::MouseEvent& event)
+{
+    dbgln("WidgetTool::on_mousemove");
+}
+
+void WidgetTool::on_keydown([[maybe_unused]] GUI::KeyEvent& event)
+{
+    dbgln("WidgetTool::on_keydown");
+}
+
+}

Userland/DevTools/HackStudio/WidgetTool.h

@@ -0,0 +1,52 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include "Tool.h"
+
+namespace HackStudio {
+
+class WidgetTool final : public Tool {
+public:
+    explicit WidgetTool(FormEditorWidget& editor, const GUI::WidgetClassRegistration& meta_class)
+        : Tool(editor)
+        , m_meta_class(meta_class)
+    {
+    }
+    virtual ~WidgetTool() override { }
+
+private:
+    virtual const char* class_name() const override { return "WidgetTool"; }
+    virtual void on_mousedown(GUI::MouseEvent&) override;
+    virtual void on_mouseup(GUI::MouseEvent&) override;
+    virtual void on_mousemove(GUI::MouseEvent&) override;
+    virtual void on_keydown(GUI::KeyEvent&) override;
+
+    const GUI::WidgetClassRegistration& m_meta_class;
+};
+
+}

Userland/DevTools/HackStudio/WidgetTreeModel.cpp

@@ -0,0 +1,117 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "WidgetTreeModel.h"
+#include <AK/StringBuilder.h>
+#include <LibGUI/Widget.h>
+
+namespace HackStudio {
+
+WidgetTreeModel::WidgetTreeModel(GUI::Widget& root)
+    : m_root(root)
+{
+    m_widget_icon.set_bitmap_for_size(16, Gfx::Bitmap::load_from_file("/res/icons/16x16/inspector-object.png"));
+}
+
+WidgetTreeModel::~WidgetTreeModel()
+{
+}
+
+GUI::ModelIndex WidgetTreeModel::index(int row, int column, const GUI::ModelIndex& parent) const
+{
+    if (!parent.is_valid()) {
+        return create_index(row, column, m_root.ptr());
+    }
+    auto& parent_node = *static_cast<GUI::Widget*>(parent.internal_data());
+    return create_index(row, column, parent_node.child_widgets().at(row));
+}
+
+GUI::ModelIndex WidgetTreeModel::parent_index(const GUI::ModelIndex& index) const
+{
+    if (!index.is_valid())
+        return {};
+    auto& widget = *static_cast<GUI::Widget*>(index.internal_data());
+    if (&widget == m_root.ptr())
+        return {};
+
+    if (widget.parent_widget() == m_root.ptr())
+        return create_index(0, 0, m_root.ptr());
+
+    // Walk the grandparent's children to find the index of widget's parent in its parent.
+    // (This is needed to produce the row number of the GUI::ModelIndex corresponding to widget's parent.)
+    int grandparent_child_index = 0;
+    for (auto& grandparent_child : widget.parent_widget()->parent_widget()->child_widgets()) {
+        if (grandparent_child == widget.parent_widget())
+            return create_index(grandparent_child_index, 0, widget.parent_widget());
+        ++grandparent_child_index;
+    }
+
+    ASSERT_NOT_REACHED();
+    return {};
+}
+
+int WidgetTreeModel::row_count(const GUI::ModelIndex& index) const
+{
+    if (!index.is_valid())
+        return 1;
+    auto& widget = *static_cast<GUI::Widget*>(index.internal_data());
+    return widget.child_widgets().size();
+}
+
+int WidgetTreeModel::column_count(const GUI::ModelIndex&) const
+{
+    return 1;
+}
+
+GUI::Variant WidgetTreeModel::data(const GUI::ModelIndex& index, GUI::ModelRole role) const
+{
+    auto* widget = static_cast<GUI::Widget*>(index.internal_data());
+    if (role == GUI::ModelRole::Icon) {
+        return m_widget_icon;
+    }
+    if (role == GUI::ModelRole::Display) {
+        return String::formatted("{} ({})", widget->class_name(), widget->relative_rect());
+    }
+    return {};
+}
+
+void WidgetTreeModel::update()
+{
+    did_update();
+}
+
+GUI::ModelIndex WidgetTreeModel::index_for_widget(GUI::Widget& widget) const
+{
+    int parent_child_index = 0;
+    for (auto& parent_child : widget.parent_widget()->child_widgets()) {
+        if (parent_child == &widget)
+            return create_index(parent_child_index, 0, &widget);
+        ++parent_child_index;
+    }
+    return {};
+}
+
+}

Userland/DevTools/HackStudio/WidgetTreeModel.h

@@ -0,0 +1,55 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <LibGUI/Model.h>
+#include <LibGUI/Painter.h>
+
+namespace HackStudio {
+
+class WidgetTreeModel final : public GUI::Model {
+public:
+    static NonnullRefPtr<WidgetTreeModel> create(GUI::Widget& root) { return adopt(*new WidgetTreeModel(root)); }
+    virtual ~WidgetTreeModel() override;
+
+    virtual int row_count(const GUI::ModelIndex& = GUI::ModelIndex()) const override;
+    virtual int column_count(const GUI::ModelIndex& = GUI::ModelIndex()) const override;
+    virtual GUI::Variant data(const GUI::ModelIndex&, GUI::ModelRole) const override;
+    virtual GUI::ModelIndex index(int row, int column, const GUI::ModelIndex& parent = GUI::ModelIndex()) const override;
+    virtual GUI::ModelIndex parent_index(const GUI::ModelIndex&) const override;
+    virtual void update() override;
+
+    GUI::ModelIndex index_for_widget(GUI::Widget&) const;
+
+private:
+    explicit WidgetTreeModel(GUI::Widget&);
+
+    NonnullRefPtr<GUI::Widget> m_root;
+    GUI::Icon m_widget_icon;
+};
+
+}

Userland/DevTools/HackStudio/main.cpp

@@ -0,0 +1,171 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "HackStudio.h"
+#include "HackStudioWidget.h"
+#include "Project.h"
+#include <AK/StringBuilder.h>
+#include <LibCore/ArgsParser.h>
+#include <LibCore/Event.h>
+#include <LibCore/EventLoop.h>
+#include <LibCore/File.h>
+#include <LibGUI/Application.h>
+#include <LibGUI/MenuBar.h>
+#include <LibGUI/MessageBox.h>
+#include <LibGUI/Widget.h>
+#include <LibGUI/Window.h>
+#include <LibThread/Lock.h>
+#include <LibThread/Thread.h>
+#include <LibVT/TerminalWidget.h>
+#include <fcntl.h>
+#include <spawn.h>
+#include <stdio.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+using namespace HackStudio;
+
+static RefPtr<GUI::Window> s_window;
+static RefPtr<HackStudioWidget> s_hack_studio_widget;
+
+static bool make_is_available();
+static void update_path_environment_variable();
+
+int main(int argc, char** argv)
+{
+    if (pledge("stdio tty accept rpath cpath wpath shared_buffer proc exec unix fattr thread unix sendfd ptrace", nullptr) < 0) {
+        perror("pledge");
+        return 1;
+    }
+
+    auto app = GUI::Application::construct(argc, argv);
+
+    if (pledge("stdio tty accept rpath cpath wpath shared_buffer proc exec fattr thread unix sendfd ptrace", nullptr) < 0) {
+        perror("pledge");
+        return 1;
+    }
+
+    s_window = GUI::Window::construct();
+    s_window->resize(840, 600);
+    s_window->set_icon(Gfx::Bitmap::load_from_file("/res/icons/16x16/app-hack-studio.png"));
+
+    update_path_environment_variable();
+
+    if (!make_is_available())
+        GUI::MessageBox::show(s_window, "The 'make' command is not available. You probably want to install the binutils, gcc, and make ports from the root of the Serenity repository.", "Error", GUI::MessageBox::Type::Error);
+
+    const char* path_argument = nullptr;
+    Core::ArgsParser args_parser;
+    args_parser.add_positional_argument(path_argument, "Path to a workspace or a file", "path", Core::ArgsParser::Required::No);
+    args_parser.parse(argc, argv);
+
+    auto argument_absolute_path = Core::File::real_path_for(path_argument);
+
+    auto project_path = argument_absolute_path;
+    if (argument_absolute_path.is_null())
+        project_path = Core::File::real_path_for(".");
+
+    s_hack_studio_widget = s_window->set_main_widget<HackStudioWidget>(project_path);
+
+    s_window->set_title(String::formatted("{} - Hack Studio", s_hack_studio_widget->project().name()));
+
+    auto menubar = GUI::MenuBar::construct();
+    s_hack_studio_widget->initialize_menubar(menubar);
+    app->set_menubar(menubar);
+
+    s_window->show();
+
+    s_hack_studio_widget->update_actions();
+
+    return app->exec();
+}
+
+static bool make_is_available()
+{
+    pid_t pid;
+    const char* argv[] = { "make", "--version", nullptr };
+    posix_spawn_file_actions_t action;
+    posix_spawn_file_actions_init(&action);
+    posix_spawn_file_actions_addopen(&action, STDOUT_FILENO, "/dev/null", O_WRONLY, 0);
+
+    if ((errno = posix_spawnp(&pid, "make", &action, nullptr, const_cast<char**>(argv), environ))) {
+        perror("posix_spawn");
+        return false;
+    }
+    int wstatus;
+    waitpid(pid, &wstatus, 0);
+    posix_spawn_file_actions_destroy(&action);
+    return WEXITSTATUS(wstatus) == 0;
+}
+
+static void update_path_environment_variable()
+{
+    StringBuilder path;
+    path.append(getenv("PATH"));
+    if (path.length())
+        path.append(":");
+    path.append("/bin:/usr/bin:/usr/local/bin");
+    setenv("PATH", path.to_string().characters(), true);
+}
+
+namespace HackStudio {
+
+GUI::TextEditor& current_editor()
+{
+    return s_hack_studio_widget->current_editor();
+}
+
+void open_file(const String& file_name)
+{
+    return s_hack_studio_widget->open_file(file_name);
+}
+
+RefPtr<EditorWrapper> current_editor_wrapper()
+{
+    if (!s_hack_studio_widget)
+        return nullptr;
+    return s_hack_studio_widget->current_editor_wrapper();
+}
+
+Project& project()
+{
+    return s_hack_studio_widget->project();
+}
+
+String currently_open_file()
+{
+    if (!s_hack_studio_widget)
+        return {};
+    return s_hack_studio_widget->currently_open_file();
+}
+
+void set_current_editor_wrapper(RefPtr<EditorWrapper> wrapper)
+{
+    s_hack_studio_widget->set_current_editor_wrapper(wrapper);
+}
+
+}