AK: Simplify constructors and conversions from nullptr_t

Problem:
- Many constructors are defined as `{}` rather than using the ` =
  default` compiler-provided constructor.
- Some types provide an implicit conversion operator from `nullptr_t`
  instead of requiring the caller to default construct. This violates
  the C++ Core Guidelines suggestion to declare single-argument
  constructors explicit
  (https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#c46-by-default-declare-single-argument-constructors-explicit).

Solution:
- Change default constructors to use the compiler-provided default
  constructor.
- Remove implicit conversion operators from `nullptr_t` and change
  usage to enforce type consistency without conversion.

Libraries/LibCore/Event.cpp

@@ -24,6 +24,7 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
+#include <AK/WeakPtr.h>
 #include <LibCore/Event.h>
 #include <LibCore/Object.h>
 
@@ -32,7 +33,7 @@ namespace Core {
 ChildEvent::ChildEvent(Type type, Object& child, Object* insertion_before_child)
     : Core::Event(type)
     , m_child(child.make_weak_ptr())
-    , m_insertion_before_child(insertion_before_child ? insertion_before_child->make_weak_ptr() : nullptr)
+    , m_insertion_before_child(AK::try_make_weak_ptr(insertion_before_child))
 {
 }
 

Libraries/LibCore/EventLoop.cpp

@@ -503,7 +503,7 @@ bool SignalHandlers::remove(int handler_id)
         auto it = m_handlers.find(handler_id);
         if (it != m_handlers.end()) {
             // Mark pending remove
-            m_handlers_pending.set(handler_id, nullptr);
+            m_handlers_pending.set(handler_id, {});
             return true;
         }
         it = m_handlers_pending.find(handler_id);

Libraries/LibCore/Object.h

@@ -256,7 +256,7 @@ const LogStream& operator<<(const LogStream&, const Object&);
     register_property(                                           \
         property_name,                                           \
         [this] { return this->getter(); },                       \
-        nullptr);
+        {});
 
 #define REGISTER_RECT_PROPERTY(property_name, getter, setter)          \
     register_property(                                                 \

Libraries/LibCoreDump/Reader.cpp

@@ -37,7 +37,7 @@ OwnPtr<Reader> Reader::create(const String& path)
 {
     auto file_or_error = MappedFile::map(path);
     if (file_or_error.is_error())
-        return nullptr;
+        return {};
     return adopt_own(*new Reader(file_or_error.release_value()));
 }
 

Libraries/LibDebug/DebugSession.cpp

@@ -90,12 +90,12 @@ OwnPtr<DebugSession> DebugSession::exec_and_attach(const String& command, String
 
     if (waitpid(pid, nullptr, WSTOPPED) != pid) {
         perror("waitpid");
-        return nullptr;
+        return {};
     }
 
     if (ptrace(PT_ATTACH, pid, 0, 0) < 0) {
         perror("PT_ATTACH");
-        return nullptr;
+        return {};
     }
 
     // We want to continue until the exit from the 'execve' sycsall.
@@ -105,7 +105,7 @@ OwnPtr<DebugSession> DebugSession::exec_and_attach(const String& command, String
 
     if (waitpid(pid, nullptr, WSTOPPED) != pid) {
         perror("wait_pid");
-        return nullptr;
+        return {};
     }
 
     auto debug_session = adopt_own(*new DebugSession(pid, source_root));
@@ -114,7 +114,7 @@ OwnPtr<DebugSession> DebugSession::exec_and_attach(const String& command, String
     int wstatus = debug_session->continue_debuggee_and_wait();
     if (WSTOPSIG(wstatus) != SIGTRAP) {
         dbgln("expected SIGTRAP");
-        return nullptr;
+        return {};
     }
 
     // At this point, libraries should have been loaded

Libraries/LibGUI/Action.cpp

@@ -24,6 +24,7 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
+#include <AK/WeakPtr.h>
 #include <LibGUI/AboutDialog.h>
 #include <LibGUI/Action.h>
 #include <LibGUI/ActionGroup.h>
@@ -39,7 +40,7 @@ namespace CommonActions {
 
 NonnullRefPtr<Action> make_about_action(const String& app_name, const Icon& app_icon, Window* parent)
 {
-    WeakPtr<Window> weak_parent = parent ? parent->make_weak_ptr<Window>() : nullptr;
+    auto weak_parent = AK::try_make_weak_ptr<Window>(parent);
     return Action::create(String::formatted("About {}", app_name), app_icon.bitmap_for_size(16), [=](auto&) {
         AboutDialog::show(app_name, app_icon.bitmap_for_size(32), weak_parent.ptr());
     });
@@ -288,7 +289,7 @@ void Action::set_checked(bool checked)
 
 void Action::set_group(Badge<ActionGroup>, ActionGroup* group)
 {
-    m_action_group = group ? group->make_weak_ptr() : nullptr;
+    m_action_group = AK::try_make_weak_ptr(group);
 }
 
 void Action::set_icon(const Gfx::Bitmap* icon)

Libraries/LibIPC/Connection.h

@@ -171,7 +171,7 @@ protected:
             if (!drain_messages_from_peer())
                 break;
         }
-        return nullptr;
+        return {};
     }
 
     bool drain_messages_from_peer()

Libraries/LibJS/Runtime/ArrayBufferPrototype.cpp

@@ -43,7 +43,7 @@ void ArrayBufferPrototype::initialize(GlobalObject& global_object)
     u8 attr = Attribute::Writable | Attribute::Configurable;
     define_native_function(vm.names.slice, slice, 2, attr);
     // FIXME: This should be an accessor property
-    define_native_property(vm.names.byteLength, byte_length_getter, nullptr, Attribute::Configurable);
+    define_native_property(vm.names.byteLength, byte_length_getter, {}, Attribute::Configurable);
 
     define_property(vm.well_known_symbol_to_string_tag(), js_string(vm.heap(), "ArrayBuffer"), Attribute::Configurable);
 }

Libraries/LibJS/Runtime/ErrorPrototype.cpp

@@ -45,7 +45,7 @@ void ErrorPrototype::initialize(GlobalObject& global_object)
     Object::initialize(global_object);
     u8 attr = Attribute::Writable | Attribute::Configurable;
     define_native_property(vm.names.name, name_getter, name_setter, attr);
-    define_native_property(vm.names.message, message_getter, nullptr, attr);
+    define_native_property(vm.names.message, message_getter, {}, attr);
     define_native_function(vm.names.toString, to_string, 0, attr);
 }
 

Libraries/LibJS/Runtime/RegExpPrototype.cpp

@@ -50,11 +50,11 @@ void RegExpPrototype::initialize(GlobalObject& global_object)
     define_native_function(vm.names.exec, exec, 1, attr);
 
     u8 readable_attr = Attribute::Configurable;
-    define_native_property(vm.names.flags, flags, nullptr, readable_attr);
-    define_native_property(vm.names.source, source, nullptr, readable_attr);
+    define_native_property(vm.names.flags, flags, {}, readable_attr);
+    define_native_property(vm.names.source, source, {}, readable_attr);
 
 #define __JS_ENUMERATE(flagName, flag_name, flag_char, ECMAScriptFlagName) \
-    define_native_property(vm.names.flagName, flag_name, nullptr, readable_attr);
+    define_native_property(vm.names.flagName, flag_name, {}, readable_attr);
     JS_ENUMERATE_REGEXP_FLAGS
 #undef __JS_ENUMERATE
 }

Libraries/LibJS/Runtime/ScriptFunction.cpp

@@ -73,8 +73,8 @@ void ScriptFunction::initialize(GlobalObject& global_object)
         prototype->define_property(vm.names.constructor, this, Attribute::Writable | Attribute::Configurable);
         define_property(vm.names.prototype, prototype, Attribute::Writable);
     }
-    define_native_property(vm.names.length, length_getter, nullptr, Attribute::Configurable);
-    define_native_property(vm.names.name, name_getter, nullptr, Attribute::Configurable);
+    define_native_property(vm.names.length, length_getter, {}, Attribute::Configurable);
+    define_native_property(vm.names.name, name_getter, {}, Attribute::Configurable);
 }
 
 ScriptFunction::~ScriptFunction()

Libraries/LibJS/Runtime/StringPrototype.cpp

@@ -82,7 +82,7 @@ void StringPrototype::initialize(GlobalObject& global_object)
     StringObject::initialize(global_object);
     u8 attr = Attribute::Writable | Attribute::Configurable;
 
-    define_native_property(vm.names.length, length_getter, nullptr, 0);
+    define_native_property(vm.names.length, length_getter, {}, 0);
     define_native_function(vm.names.charAt, char_at, 1, attr);
     define_native_function(vm.names.charCodeAt, char_code_at, 1, attr);
     define_native_function(vm.names.repeat, repeat, 1, attr);

Libraries/LibJS/Runtime/SymbolPrototype.cpp

@@ -47,7 +47,7 @@ void SymbolPrototype::initialize(GlobalObject& global_object)
 {
     auto& vm = this->vm();
     Object::initialize(global_object);
-    define_native_property(vm.names.description, description_getter, nullptr, Attribute::Configurable);
+    define_native_property(vm.names.description, description_getter, {}, Attribute::Configurable);
     define_native_function(vm.names.toString, to_string, 0, Attribute::Writable | Attribute::Configurable);
     define_native_function(vm.names.valueOf, value_of, 0, Attribute::Writable | Attribute::Configurable);
 

Libraries/LibJS/Runtime/TypedArrayPrototype.cpp

@@ -40,7 +40,7 @@ void TypedArrayPrototype::initialize(GlobalObject& object)
     auto& vm = this->vm();
     Object::initialize(object);
     // FIXME: This should be an accessor property
-    define_native_property(vm.names.length, length_getter, nullptr, Attribute::Configurable);
+    define_native_property(vm.names.length, length_getter, {}, Attribute::Configurable);
 }
 
 TypedArrayPrototype::~TypedArrayPrototype()

Libraries/LibJS/Runtime/Uint8ClampedArray.cpp

@@ -42,7 +42,7 @@ Uint8ClampedArray::Uint8ClampedArray(u32 length, Object& prototype)
     , m_length(length)
 {
     auto& vm = this->vm();
-    define_native_property(vm.names.length, length_getter, nullptr);
+    define_native_property(vm.names.length, length_getter, {});
     m_data = (u8*)calloc(m_length, 1);
 }
 

Libraries/LibLine/InternalFunctions.cpp

@@ -43,7 +43,7 @@ Function<bool(Editor&)> Editor::find_internal_function(const StringView& name)
 
     ENUMERATE_EDITOR_INTERNAL_FUNCTIONS(__ENUMERATE)
 
-    return nullptr;
+    return {};
 }
 
 void Editor::search_forwards()

Libraries/LibMarkdown/CodeBlock.cpp

@@ -112,13 +112,13 @@ String CodeBlock::render_for_terminal(size_t) const
 OwnPtr<CodeBlock> CodeBlock::parse(Vector<StringView>::ConstIterator& lines)
 {
     if (lines.is_end())
-        return nullptr;
+        return {};
 
     constexpr auto tick_tick_tick = "```";
 
     StringView line = *lines;
     if (!line.starts_with(tick_tick_tick))
-        return nullptr;
+        return {};
 
     // Our Markdown extension: we allow
     // specifying a style and a language
@@ -134,7 +134,7 @@ OwnPtr<CodeBlock> CodeBlock::parse(Vector<StringView>::ConstIterator& lines)
     StringView style_spec = line.substring_view(3, line.length() - 3);
     auto spec = Text::parse(style_spec);
     if (!spec.has_value())
-        return nullptr;
+        return {};
 
     ++lines;
 

Libraries/LibMarkdown/Document.cpp

@@ -119,7 +119,7 @@ OwnPtr<Document> Document::parse(const StringView& str)
 
         auto line = Paragraph::Line::parse(lines);
         if (!line)
-            return nullptr;
+            return {};
 
         paragraph_lines.append(line.release_nonnull());
     }

Libraries/LibMarkdown/Heading.cpp

@@ -62,7 +62,7 @@ String Heading::render_for_terminal(size_t) const
 OwnPtr<Heading> Heading::parse(Vector<StringView>::ConstIterator& lines)
 {
     if (lines.is_end())
-        return nullptr;
+        return {};
 
     const StringView& line = *lines;
     size_t level;
@@ -73,12 +73,12 @@ OwnPtr<Heading> Heading::parse(Vector<StringView>::ConstIterator& lines)
     }
 
     if (!level || level >= line.length() || line[level] != ' ')
-        return nullptr;
+        return {};
 
     StringView title_view = line.substring_view(level + 1, line.length() - level - 1);
     auto text = Text::parse(title_view);
     if (!text.has_value())
-        return nullptr;
+        return {};
 
     auto heading = make<Heading>(move(text.value()), level);
 

Libraries/LibMarkdown/HorizontalRule.cpp

@@ -47,19 +47,19 @@ String HorizontalRule::render_for_terminal(size_t view_width) const
 OwnPtr<HorizontalRule> HorizontalRule::parse(Vector<StringView>::ConstIterator& lines)
 {
     if (lines.is_end())
-        return nullptr;
+        return {};
 
     const StringView& line = *lines;
 
     if (line.length() < 3)
-        return nullptr;
+        return {};
     if (!line.starts_with('-') && !line.starts_with('_') && !line.starts_with('*'))
-        return nullptr;
+        return {};
 
     auto first_character = line.characters_without_null_termination()[0];
     for (auto ch : line) {
         if (ch != first_character)
-            return nullptr;
+            return {};
     }
 
     ++lines;

Libraries/LibMarkdown/List.cpp

@@ -122,20 +122,20 @@ OwnPtr<List> List::parse(Vector<StringView>::ConstIterator& lines)
             if (first)
                 is_ordered = appears_ordered;
             else if (is_ordered != appears_ordered)
-                return nullptr;
+                return {};
 
             if (!flush_item_if_needed())
-                return nullptr;
+                return {};
 
             while (offset + 1 < line.length() && line[offset + 1] == ' ')
                 offset++;
 
         } else {
             if (first)
-                return nullptr;
+                return {};
             for (size_t i = 0; i < offset; i++) {
                 if (line[i] != ' ')
-                    return nullptr;
+                    return {};
             }
         }
 
@@ -149,7 +149,7 @@ OwnPtr<List> List::parse(Vector<StringView>::ConstIterator& lines)
     }
 
     if (!flush_item_if_needed() || first)
-        return nullptr;
+        return {};
     return make<List>(move(items), is_ordered);
 }
 

Libraries/LibMarkdown/Paragraph.cpp

@@ -61,11 +61,11 @@ String Paragraph::render_for_terminal(size_t) const
 OwnPtr<Paragraph::Line> Paragraph::Line::parse(Vector<StringView>::ConstIterator& lines)
 {
     if (lines.is_end())
-        return nullptr;
+        return {};
 
     auto text = Text::parse(*lines++);
     if (!text.has_value())
-        return nullptr;
+        return {};
 
     return make<Paragraph::Line>(text.release_value());
 }

Libraries/LibMarkdown/Table.cpp

@@ -118,12 +118,12 @@ OwnPtr<Table> Table::parse(Vector<StringView>::ConstIterator& lines)
     auto peek_it = lines;
     auto first_line = *peek_it;
     if (!first_line.starts_with('|'))
-        return nullptr;
+        return {};
 
     ++peek_it;
 
     if (peek_it.is_end())
-        return nullptr;
+        return {};
 
     auto header_segments = first_line.split_view('|', true);
     auto header_delimiters = peek_it->split_view('|', true);
@@ -141,10 +141,10 @@ OwnPtr<Table> Table::parse(Vector<StringView>::ConstIterator& lines)
     ++peek_it;
 
     if (header_delimiters.size() != header_segments.size())
-        return nullptr;
+        return {};
 
     if (header_delimiters.is_empty())
-        return nullptr;
+        return {};
 
     size_t total_width = 0;
 
@@ -154,7 +154,7 @@ OwnPtr<Table> Table::parse(Vector<StringView>::ConstIterator& lines)
     for (size_t i = 0; i < header_segments.size(); ++i) {
         auto text_option = Text::parse(header_segments[i]);
         if (!text_option.has_value())
-            return nullptr; // An invalid 'text' in the header should just fail the table parse.
+            return {}; // An invalid 'text' in the header should just fail the table parse.
 
         auto text = text_option.release_value();
         auto& column = table->m_columns[i];

Libraries/LibPCIDB/Database.cpp

@@ -138,10 +138,10 @@ int Database::init()
 
     ParseMode mode = ParseMode::UnknownMode;
 
-    OwnPtr<Vendor> current_vendor = nullptr;
-    OwnPtr<Device> current_device = nullptr;
-    OwnPtr<Class> current_class = nullptr;
-    OwnPtr<Subclass> current_subclass = nullptr;
+    OwnPtr<Vendor> current_vendor {};
+    OwnPtr<Device> current_device {};
+    OwnPtr<Class> current_class {};
+    OwnPtr<Subclass> current_subclass {};
 
     auto commit_device = [&]() {
         if (current_device && current_vendor) {

Libraries/LibRegex/C/Regex.cpp

@@ -69,7 +69,7 @@ int regcomp(regex_t* reg, const char* pattern, int cflags)
 
     // Note that subsequent uses of regcomp() without regfree() _will_ leak memory
     // This could've been prevented if libc provided a reginit() or similar, but it does not.
-    reg->__data = new internal_regex_t { 0, 0, nullptr, 0, ReError::REG_NOERR, {}, 0 };
+    reg->__data = new internal_regex_t { 0, 0, {}, 0, ReError::REG_NOERR, {}, 0 };
 
     auto preg = impl_from(reg);
 

Libraries/LibWeb/HTML/CanvasRenderingContext2D.cpp

@@ -142,11 +142,11 @@ void CanvasRenderingContext2D::did_draw(const Gfx::FloatRect&)
 OwnPtr<Gfx::Painter> CanvasRenderingContext2D::painter()
 {
     if (!m_element)
-        return nullptr;
+        return {};
 
     if (!m_element->bitmap()) {
         if (!m_element->create_bitmap())
-            return nullptr;
+            return {};
     }
 
     return make<Gfx::Painter>(*m_element->bitmap());
@@ -208,7 +208,7 @@ RefPtr<ImageData> CanvasRenderingContext2D::create_image_data(int width, int hei
 {
     if (!wrapper()) {
         dbgln("Hmm! Attempted to create ImageData for wrapper-less CRC2D.");
-        return nullptr;
+        return {};
     }
     return ImageData::create_with_size(wrapper()->global_object(), width, height);
 }