LibGUI: Turn GUI::Application::the() into a pointer

During app teardown, the Application object may be destroyed before
something else, and so having Application::the() return a reference was
obscuring the truth about its lifetime.

This patch makes the API more honest by returning a pointer. While
this makes call sites look a bit more sketchy, do note that the global
Application pointer only becomes null during app teardown.

Applications/Browser/Tab.cpp

@@ -254,7 +254,7 @@ Tab::Tab()
     app_menu.add_action(*m_reload_action);
     app_menu.add_separator();
     app_menu.add_action(GUI::CommonActions::make_quit_action([](auto&) {
-        GUI::Application::the().quit();
+        GUI::Application::the()->quit();
     }));
 
     auto& view_menu = m_menubar->add_menu("View");
@@ -429,7 +429,7 @@ void Tab::did_become_active()
     m_toolbar_container->set_visible(!is_fullscreen);
     m_statusbar->set_visible(!is_fullscreen);
 
-    GUI::Application::the().set_menubar(m_menubar);
+    GUI::Application::the()->set_menubar(m_menubar);
 }
 
 void Tab::context_menu_requested(const Gfx::IntPoint& screen_position)

Applications/Calculator/main.cpp

@@ -69,7 +69,7 @@ int main(int argc, char** argv)
 
     auto& app_menu = menubar->add_menu("Calculator");
     app_menu.add_action(GUI::CommonActions::make_quit_action([](auto&) {
-        GUI::Application::the().quit(0);
+        GUI::Application::the()->quit();
         return;
     }));
 

Applications/Calendar/main.cpp

@@ -74,7 +74,7 @@ int main(int argc, char** argv)
         }));
 
     app_menu.add_action(GUI::CommonActions::make_quit_action([](auto&) {
-        GUI::Application::the().quit(0);
+        GUI::Application::the()->quit();
         return;
     }));
 

Applications/DisplaySettings/DisplaySettings.cpp

@@ -247,7 +247,7 @@ void DisplaySettingsWidget::create_frame()
     ok_button.set_preferred_size(60, 22);
     ok_button.on_click = [this](auto) {
         send_settings_to_window_server();
-        GUI::Application::the().quit();
+        GUI::Application::the()->quit();
     };
 
     auto& cancel_button = bottom_widget.add<GUI::Button>();
@@ -255,7 +255,7 @@ void DisplaySettingsWidget::create_frame()
     cancel_button.set_size_policy(Orientation::Horizontal, GUI::SizePolicy::Fixed);
     cancel_button.set_preferred_size(60, 22);
     cancel_button.on_click = [](auto) {
-        GUI::Application::the().quit();
+        GUI::Application::the()->quit();
     };
 
     auto& apply_button = bottom_widget.add<GUI::Button>();

Applications/FileManager/main.cpp

@@ -225,7 +225,7 @@ int run_in_desktop_mode(RefPtr<Core::ConfigFile> config, String initial_location
     };
 
     window->show();
-    return GUI::Application::the().exec();
+    return GUI::Application::the()->exec();
 }
 
 int run_in_windowed_mode(RefPtr<Core::ConfigFile> config, String initial_location)
@@ -627,7 +627,7 @@ int run_in_windowed_mode(RefPtr<Core::ConfigFile> config, String initial_locatio
     app_menu.add_action(properties_action);
     app_menu.add_separator();
     app_menu.add_action(GUI::CommonActions::make_quit_action([](auto&) {
-        GUI::Application::the().quit(0);
+        GUI::Application::the()->quit();
     }));
 
     auto& view_menu = menubar->add_menu("View");
@@ -646,7 +646,7 @@ int run_in_windowed_mode(RefPtr<Core::ConfigFile> config, String initial_locatio
         GUI::AboutDialog::show("File Manager", Gfx::Bitmap::load_from_file("/res/icons/32x32/filetype-folder.png"), window);
     }));
 
-    GUI::Application::the().set_menubar(move(menubar));
+    GUI::Application::the()->set_menubar(move(menubar));
 
     main_toolbar.add_action(go_back_action);
     main_toolbar.add_action(go_forward_action);
@@ -856,5 +856,5 @@ int run_in_windowed_mode(RefPtr<Core::ConfigFile> config, String initial_locatio
         return GUI::Window::CloseRequestDecision::Close;
     };
 
-    return GUI::Application::the().exec();
+    return GUI::Application::the()->exec();
 }

Applications/FontEditor/main.cpp

@@ -86,8 +86,8 @@ int main(int argc, char** argv)
     auto menubar = GUI::MenuBar::construct();
 
     auto& app_menu = menubar->add_menu("Font Editor");
-    app_menu.add_action(GUI::CommonActions::make_quit_action([](auto&) {
+    app_menu.add_action(GUI::CommonActions::make_quit_action([&](auto&) {
-        GUI::Application::the().quit(0);
+        app->quit();
         return;
     }));
 

Applications/Help/main.cpp

@@ -194,7 +194,7 @@ int main(int argc, char* argv[])
     }));
     app_menu.add_separator();
     app_menu.add_action(GUI::CommonActions::make_quit_action([](auto&) {
-        GUI::Application::the().quit(0);
+        GUI::Application::the()->quit();
     }));
 
     auto& go_menu = menubar->add_menu("Go");

Applications/HexEditor/HexEditorWidget.cpp

@@ -142,7 +142,7 @@ HexEditorWidget::HexEditorWidget()
     app_menu.add_action(GUI::CommonActions::make_quit_action([this](auto&) {
         if (!request_close())
             return;
-        GUI::Application::the().quit(0);
+        GUI::Application::the()->quit();
     }));
 
     m_goto_decimal_offset_action = GUI::Action::create("Go To Offset (Decimal)...", { Mod_Ctrl | Mod_Shift, Key_G }, Gfx::Bitmap::load_from_file("/res/icons/16x16/go-forward.png"), [this](const GUI::Action&) {
@@ -199,7 +199,7 @@ HexEditorWidget::HexEditorWidget()
         GUI::AboutDialog::show("Hex Editor", Gfx::Bitmap::load_from_file("/res/icons/32x32/app-hexeditor.png"), window());
     }));
 
-    GUI::Application::the().set_menubar(move(menubar));
+    GUI::Application::the()->set_menubar(move(menubar));
 
     m_editor->set_focus(true);
 }

Applications/IRCClient/IRCAppWindow.cpp

@@ -263,7 +263,7 @@ void IRCAppWindow::setup_menus()
     auto& app_menu = menubar->add_menu("IRC Client");
     app_menu.add_action(GUI::CommonActions::make_quit_action([](auto&) {
         dbgprintf("Terminal: Quit menu activated!\n");
-        GUI::Application::the().quit(0);
+        GUI::Application::the()->quit();
         return;
     }));
 
@@ -301,7 +301,7 @@ void IRCAppWindow::setup_menus()
         GUI::AboutDialog::show("IRC Client", Gfx::Bitmap::load_from_file("/res/icons/32x32/app-irc-client.png"), this);
     }));
 
-    GUI::Application::the().set_menubar(move(menubar));
+    GUI::Application::the()->set_menubar(move(menubar));
 }
 
 void IRCAppWindow::setup_widgets()

Applications/Piano/main.cpp

@@ -96,7 +96,7 @@ int main(int argc, char** argv)
 
     auto& app_menu = menubar->add_menu("Piano");
     app_menu.add_action(GUI::CommonActions::make_quit_action([](auto&) {
-        GUI::Application::the().quit(0);
+        GUI::Application::the()->quit();
         return;
     }));
     app_menu.add_action(GUI::Action::create("Export", { Mod_Ctrl, Key_E }, [&](const GUI::Action&) {

Applications/PixelPaint/main.cpp

@@ -113,7 +113,7 @@ int main(int argc, char** argv)
     }));
     app_menu.add_separator();
     app_menu.add_action(GUI::CommonActions::make_quit_action([](auto&) {
-        GUI::Application::the().quit(0);
+        GUI::Application::the()->quit();
         return;
     }));
 

Applications/SystemMonitor/main.cpp

@@ -223,7 +223,7 @@ int main(int argc, char** argv)
     auto menubar = GUI::MenuBar::construct();
     auto& app_menu = menubar->add_menu("System Monitor");
     app_menu.add_action(GUI::CommonActions::make_quit_action([](auto&) {
-        GUI::Application::the().quit(0);
+        GUI::Application::the()->quit();
         return;
     }));
 

Applications/Terminal/main.cpp

@@ -291,7 +291,7 @@ int main(int argc, char** argv)
     app_menu.add_separator();
     app_menu.add_action(GUI::CommonActions::make_quit_action([](auto&) {
         dbgprintf("Terminal: Quit menu activated!\n");
-        GUI::Application::the().quit(0);
+        GUI::Application::the()->quit();
     }));
 
     auto& edit_menu = menubar->add_menu("Edit");

Applications/TextEditor/TextEditorWidget.cpp

@@ -368,7 +368,7 @@ TextEditorWidget::TextEditorWidget()
     app_menu.add_action(GUI::CommonActions::make_quit_action([this](auto&) {
         if (!request_close())
             return;
-        GUI::Application::the().quit(0);
+        GUI::Application::the()->quit();
     }));
 
     auto& edit_menu = menubar->add_menu("Edit");
@@ -455,7 +455,7 @@ TextEditorWidget::TextEditorWidget()
         GUI::AboutDialog::show("Text Editor", Gfx::Bitmap::load_from_file("/res/icons/32x32/app-texteditor.png"), window());
     }));
 
-    GUI::Application::the().set_menubar(move(menubar));
+    GUI::Application::the()->set_menubar(move(menubar));
 
     toolbar.add_action(*m_new_action);
     toolbar.add_action(*m_open_action);

DevTools/Profiler/main.cpp

@@ -144,11 +144,11 @@ bool prompt_to_stop_profiling()
 
     auto& stop_button = widget.add<GUI::Button>("Stop");
     stop_button.on_click = [&](auto) {
-        GUI::Application::the().quit();
+        GUI::Application::the()->quit();
     };
 
     window->show();
-    return GUI::Application::the().exec() == 0;
+    return GUI::Application::the()->exec() == 0;
 }
 
 bool generate_profile(pid_t pid)

DevTools/VisualBuilder/main.cpp

@@ -59,7 +59,7 @@ int main(int argc, char** argv)
     auto menubar = GUI::MenuBar::construct();
     auto& app_menu = menubar->add_menu("Visual Builder");
     app_menu.add_action(GUI::CommonActions::make_quit_action([](auto&) {
-        GUI::Application::the().quit(0);
+        GUI::Application::the()->quit();
         return;
     }));
 

Games/Minesweeper/main.cpp

@@ -104,7 +104,7 @@ int main(int argc, char** argv)
     app_menu.add_separator();
 
     app_menu.add_action(GUI::CommonActions::make_quit_action([](auto&) {
-        GUI::Application::the().quit(0);
+        GUI::Application::the()->quit();
         return;
     }));
 

Games/Snake/main.cpp

@@ -65,7 +65,7 @@ int main(int argc, char** argv)
         game.reset();
     }));
     app_menu.add_action(GUI::CommonActions::make_quit_action([](auto&) {
-        GUI::Application::the().quit(0);
+        GUI::Application::the()->quit();
     }));
 
     auto& help_menu = menubar->add_menu("Help");

Libraries/LibGUI/Action.cpp

@@ -157,14 +157,17 @@ Action::Action(const StringView& text, const Shortcut& shortcut, RefPtr<Gfx::Bit
         m_scope = ShortcutScope::WindowLocal;
     } else {
         m_scope = ShortcutScope::ApplicationGlobal;
-        Application::the().register_global_shortcut_action({}, *this);
+        if (auto* app = Application::the())
+            app->register_global_shortcut_action({}, *this);
     }
 }
 
 Action::~Action()
 {
-    if (m_shortcut.is_valid() && m_scope == ShortcutScope::ApplicationGlobal)
+    if (m_shortcut.is_valid() && m_scope == ShortcutScope::ApplicationGlobal) {
-        Application::the().unregister_global_shortcut_action({}, *this);
+        if (auto* app = Application::the())
+            app->unregister_global_shortcut_action({}, *this);
+    }
 }
 
 void Action::activate(Core::Object* activator)

Libraries/LibGUI/Application.cpp

@@ -39,18 +39,17 @@
 
 namespace GUI {
 
-static Application* s_the;
+static WeakPtr<Application> s_the;
 
-Application& Application::the()
+Application* Application::the()
 {
-    ASSERT(s_the);
+    return s_the;
-    return *s_the;
 }
 
 Application::Application(int argc, char** argv)
 {
     ASSERT(!s_the);
-    s_the = this;
+    s_the = make_weak_ptr();
     m_event_loop = make<Core::EventLoop>();
     WindowServerConnection::the();
     Clipboard::initialize({});
@@ -68,7 +67,7 @@ Application::Application(int argc, char** argv)
 
 Application::~Application()
 {
-    s_the = nullptr;
+    revoke_weak_ptrs();
 }
 
 int Application::exec()

Libraries/LibGUI/Application.h

@@ -40,7 +40,7 @@ class Application : public Core::Object {
     C_OBJECT(Application);
 
 public:
-    static Application& the();
+    static Application* the();
 
     ~Application();
 

Libraries/LibGUI/Widget.cpp

@@ -98,7 +98,7 @@ Widget::Widget()
     , m_background_role(Gfx::ColorRole::Window)
     , m_foreground_role(Gfx::ColorRole::WindowText)
     , m_font(Gfx::Font::default_font())
-    , m_palette(Application::the().palette().impl())
+    , m_palette(Application::the()->palette().impl())
 {
 }
 
@@ -245,7 +245,7 @@ void Widget::handle_paint_event(PaintEvent& event)
         painter.draw_rect(rect(), Color::Magenta);
     }
 
-    if (Application::the().focus_debugging_enabled()) {
+    if (Application::the()->focus_debugging_enabled()) {
         if (is_focused()) {
             Painter painter(*this);
             painter.draw_rect(rect(), Color::Cyan);
@@ -318,13 +318,13 @@ void Widget::handle_mousedoubleclick_event(MouseEvent& event)
 void Widget::handle_enter_event(Core::Event& event)
 {
     if (has_tooltip())
-        Application::the().show_tooltip(m_tooltip, screen_relative_rect().center().translated(0, height() / 2));
+        Application::the()->show_tooltip(m_tooltip, screen_relative_rect().center().translated(0, height() / 2));
     enter_event(event);
 }
 
 void Widget::handle_leave_event(Core::Event& event)
 {
-    Application::the().hide_tooltip();
+    Application::the()->hide_tooltip();
     leave_event(event);
 }
 

Libraries/LibGUI/Window.cpp

@@ -113,7 +113,7 @@ void Window::show()
     apply_icon();
 
     reified_windows->set(m_window_id, this);
-    Application::the().did_create_window({});
+    Application::the()->did_create_window({});
     update();
 }
 
@@ -158,7 +158,7 @@ void Window::hide()
         }
     }
     if (!app_has_visible_windows)
-        Application::the().did_delete_last_window({});
+        Application::the()->did_delete_last_window({});
 }
 
 void Window::set_title(const StringView& title)

Libraries/LibGUI/WindowServerConnection.cpp

@@ -61,7 +61,7 @@ static void set_system_theme_from_shbuf_id(int id)
     auto system_theme = SharedBuffer::create_from_shbuf_id(id);
     ASSERT(system_theme);
     Gfx::set_system_theme(*system_theme);
-    Application::the().set_system_palette(*system_theme);
+    Application::the()->set_system_palette(*system_theme);
 }
 
 void WindowServerConnection::handshake()
@@ -154,7 +154,7 @@ void WindowServerConnection::handle(const Messages::WindowClient::KeyDown& messa
     }
 
     if (!action) {
-        action = Application::the().action_for_key_event(*key_event);
+        action = Application::the()->action_for_key_event(*key_event);
 #ifdef KEYBOARD_SHORTCUTS_DEBUG
         dbg() << "  > Asked application, got action: " << action;
 #endif

Libraries/LibVT/TerminalWidget.cpp

@@ -70,7 +70,7 @@ void TerminalWidget::set_pty_master_fd(int fd)
         if (nread < 0) {
             dbgprintf("Terminal read error: %s\n", strerror(errno));
             perror("read(ptm)");
-            GUI::Application::the().quit(1);
+            GUI::Application::the()->quit(1);
             return;
         }
         if (nread == 0) {

Libraries/LibWeb/PageView.cpp

@@ -221,12 +221,12 @@ void PageView::page_did_middle_click_link(const String& href, [[maybe_unused]] c
 
 void PageView::page_did_enter_tooltip_area(const Gfx::IntPoint& content_position, const String& title)
 {
-    GUI::Application::the().show_tooltip(title, screen_relative_rect().location().translated(to_widget_position(content_position)));
+    GUI::Application::the()->show_tooltip(title, screen_relative_rect().location().translated(to_widget_position(content_position)));
 }
 
 void PageView::page_did_leave_tooltip_area()
 {
-    GUI::Application::the().hide_tooltip();
+    GUI::Application::the()->hide_tooltip();
 }
 
 void PageView::page_did_hover_link(const URL& url)