LibGfx+Userland: Make Gfx::SystemTheme propagate errors

This patch introduces error propagation to Gfx::SystemTheme to remove
instances of release_value_but_fixme_should_propagate_errors().

Userland applications that have been affected by this change have been
updated to utilise this propagation and as a result 4 such instances of
the aforementioned method have been removed.

Userland/Applications/DisplaySettings/ThemePreviewWidget.cpp

@@ -19,9 +19,11 @@ ThemePreviewWidget::ThemePreviewWidget(Gfx::Palette const& palette)
     set_fixed_size(304, 201);
 }
 
-void ThemePreviewWidget::set_theme(DeprecatedString path)
+ErrorOr<void> ThemePreviewWidget::set_theme(DeprecatedString path)
 {
-    set_theme_from_file(*Core::File::open(path, Core::OpenMode::ReadOnly).release_value_but_fixme_should_propagate_errors());
+    auto config_file = TRY(Core::File::open(path, Core::OpenMode::ReadOnly));
+    TRY(set_theme_from_file(config_file));
+    return {};
 }
 
 void ThemePreviewWidget::paint_preview(GUI::PaintEvent&)

Userland/Applications/DisplaySettings/ThemePreviewWidget.h

@@ -18,7 +18,7 @@ class ThemePreviewWidget final : public GUI::AbstractThemePreview {
     C_OBJECT(ThemePreviewWidget);
 
 public:
-    void set_theme(DeprecatedString path);
+    ErrorOr<void> set_theme(DeprecatedString path);
 
 private:
     explicit ThemePreviewWidget(Gfx::Palette const& palette);

Userland/Applications/DisplaySettings/ThemesSettingsWidget.cpp

@@ -13,6 +13,7 @@
 #include <LibGUI/Application.h>
 #include <LibGUI/ConnectionToWindowServer.h>
 #include <LibGUI/ItemListModel.h>
+#include <LibGUI/MessageBox.h>
 #include <LibGUI/Process.h>
 
 namespace DisplaySettings {
@@ -21,7 +22,7 @@ ThemesSettingsWidget::ThemesSettingsWidget(bool& background_settings_changed)
     : m_background_settings_changed { background_settings_changed }
 {
     load_from_gml(themes_settings_gml);
-    m_themes = Gfx::list_installed_system_themes();
+    m_themes = MUST(Gfx::list_installed_system_themes());
 
     size_t current_theme_index;
     auto current_theme_name = GUI::ConnectionToWindowServer::the().get_system_theme();
@@ -39,7 +40,10 @@ ThemesSettingsWidget::ThemesSettingsWidget(bool& background_settings_changed)
     m_themes_combo->set_model(*GUI::ItemListModel<DeprecatedString>::create(m_theme_names));
     m_themes_combo->on_change = [this](auto&, const GUI::ModelIndex& index) {
         m_selected_theme = &m_themes.at(index.row());
-        m_theme_preview->set_theme(m_selected_theme->path);
+        auto set_theme_result = m_theme_preview->set_theme(m_selected_theme->path);
+        if (set_theme_result.is_error()) {
+            GUI::MessageBox::show_error(window(), DeprecatedString::formatted("There was an error generating the theme preview: {}", set_theme_result.error()));
+        }
         set_modified(true);
     };
     m_themes_combo->set_selected_index(current_theme_index, GUI::AllowCallback::No);
@@ -66,7 +70,10 @@ ThemesSettingsWidget::ThemesSettingsWidget(bool& background_settings_changed)
             if (current_theme_name == theme_meta.name) {
                 m_themes_combo->set_selected_index(index, GUI::AllowCallback::No);
                 m_selected_theme = &m_themes.at(index);
-                m_theme_preview->set_theme(m_selected_theme->path);
+                auto set_theme_result = m_theme_preview->set_theme(m_selected_theme->path);
+                if (set_theme_result.is_error()) {
+                    GUI::MessageBox::show_error(window(), DeprecatedString::formatted("There was an error setting the new theme: {}", set_theme_result.error()));
+                }
             }
             ++index;
         }

Userland/Applications/ThemeEditor/MainWidget.cpp

@@ -208,7 +208,11 @@ ErrorOr<void> MainWidget::initialize_menubar(GUI::Window& window)
         auto response = FileSystemAccessClient::Client::the().try_open_file(&window, "Select theme file", "/res/themes"sv);
         if (response.is_error())
             return;
-        load_from_file(*response.value());
+        auto load_from_file_result = load_from_file(*response.value());
+        if (load_from_file_result.is_error()) {
+            GUI::MessageBox::show_error(&window, DeprecatedString::formatted("Can't open file named {}: {}", response.value()->filename(), load_from_file_result.error()));
+            return;
+        }
     })));
 
     m_save_action = GUI::CommonActions::make_save_action([&](auto&) {
@@ -557,10 +561,10 @@ void MainWidget::show_path_picker_dialog(StringView property_display_name, GUI::
     path_input.set_text(*result);
 }
 
-void MainWidget::load_from_file(Core::File& file)
+ErrorOr<void> MainWidget::load_from_file(Core::File& file)
 {
-    auto config_file = Core::ConfigFile::open(file.filename(), file.leak_fd()).release_value_but_fixme_should_propagate_errors();
-    auto theme = Gfx::load_system_theme(config_file);
+    auto config_file = TRY(Core::ConfigFile::open(file.filename(), file.leak_fd()));
+    auto theme = TRY(Gfx::load_system_theme(config_file));
     VERIFY(theme.is_valid());
 
     auto new_palette = Gfx::Palette(Gfx::PaletteImpl::create_with_anonymous_buffer(theme));
@@ -599,6 +603,7 @@ void MainWidget::load_from_file(Core::File& file)
 
     m_last_modified_time = Time::now_monotonic();
     window()->set_modified(false);
+    return {};
 }
 
 }

Userland/Applications/ThemeEditor/MainWidget.h

@@ -85,7 +85,7 @@ public:
     ErrorOr<void> initialize_menubar(GUI::Window&);
     GUI::Window::CloseRequestDecision request_close();
     void update_title();
-    void load_from_file(Core::File&);
+    ErrorOr<void> load_from_file(Core::File&);
 
 private:
     MainWidget();

Userland/Applications/ThemeEditor/PreviewWidget.cpp

@@ -160,7 +160,10 @@ void PreviewWidget::drop_event(GUI::DropEvent& event)
         auto response = FileSystemAccessClient::Client::the().try_request_file(window(), urls.first().path(), Core::OpenMode::ReadOnly);
         if (response.is_error())
             return;
-        set_theme_from_file(*response.value());
+
+        auto set_theme_from_file_result = set_theme_from_file(response.release_value());
+        if (set_theme_from_file_result.is_error())
+            GUI::MessageBox::show_error(window(), DeprecatedString::formatted("Setting theme from file has failed: {}", set_theme_from_file_result.error()));
     }
 }
 

Userland/Applications/ThemeEditor/main.cpp

@@ -56,8 +56,11 @@ ErrorOr<int> serenity_main(Main::Arguments arguments)
                 auto response = FileSystemAccessClient::Client::the().try_request_file_read_only_approved(window, path.value());
                 if (response.is_error())
                     GUI::MessageBox::show_error(window, DeprecatedString::formatted("Opening \"{}\" failed: {}", path.value(), response.error()));
-                else
-                    main_widget->load_from_file(response.release_value());
+                else {
+                    auto load_from_file_result = main_widget->load_from_file(response.release_value());
+                    if (load_from_file_result.is_error())
+                        GUI::MessageBox::show_error(window, DeprecatedString::formatted("Loading theme from file has failed: {}", load_from_file_result.error()));
+                }
             });
     }