fix(engine/linux): guard GTK3-only embedder paths

engine/src/flutter/shell/platform/linux/BUILD.gn

@@ -222,7 +222,8 @@ copy("flutter_linux_gschemas") {
   outputs = [ "$target_gen_dir/assets/{{source_name_part}}/gschemas.compiled" ]
 }
 
-executable("flutter_linux_unittests") {
+if (!use_gtk4) {
+  executable("flutter_linux_unittests") {
   testonly = true
 
   sources = [
@@ -311,6 +312,7 @@ executable("flutter_linux_unittests") {
     "//flutter/shell/platform/embedder:embedder_test_utils",
     "//flutter/testing",
   ]
+  }
 }
 
 shared_library("flutter_linux_gtk") {

engine/src/flutter/shell/platform/linux/fl_application.cc

@@ -5,9 +5,11 @@
 #include "flutter/shell/platform/linux/public/flutter_linux/fl_application.h"
 
 #include <gtk/gtk.h>
+#if !FLUTTER_LINUX_GTK4
 #ifdef GDK_WINDOWING_X11
 #include <gdk/gdkx.h>
 #endif
+#endif
 
 #include "flutter/shell/platform/linux/fl_engine_private.h"
 #include "flutter/shell/platform/linux/public/flutter_linux/fl_dart_project.h"
@@ -34,7 +36,11 @@ G_DEFINE_TYPE_WITH_CODE(FlApplication,
 
 // Called when the first frame is received.
 static void first_frame_cb(FlApplication* self, FlView* view) {
+#if FLUTTER_LINUX_GTK4
+  GtkWidget* window = gtk_widget_get_root(GTK_WIDGET(view));
+#else
   GtkWidget* window = gtk_widget_get_toplevel(GTK_WIDGET(view));
+#endif
 
   // Show the main window.
   if (window != nullptr && GTK_IS_WINDOW(window)) {
@@ -61,6 +67,7 @@ static GtkWindow* fl_application_create_window(FlApplication* self,
   // if future cases occur).
   gboolean use_header_bar = TRUE;
 #ifdef GDK_WINDOWING_X11
+#if !FLUTTER_LINUX_GTK4
   GdkScreen* screen = gtk_window_get_screen(GTK_WINDOW(window));
   if (GDK_IS_X11_SCREEN(screen)) {
     const gchar* wm_name = gdk_x11_screen_get_window_manager_name(screen);
@@ -68,6 +75,7 @@ static GtkWindow* fl_application_create_window(FlApplication* self,
       use_header_bar = FALSE;
     }
   }
+#endif
 #endif
   if (use_header_bar) {
     GtkHeaderBar* header_bar = GTK_HEADER_BAR(gtk_header_bar_new());

engine/src/flutter/shell/platform/linux/fl_opengl_manager.cc

@@ -3,8 +3,13 @@
 // found in the LICENSE file.
 
 #include <epoxy/egl.h>
+#if FLUTTER_LINUX_GTK4
+#include <gdk/wayland/gdkwayland.h>
+#include <gdk/x11/gdkx.h>
+#else
 #include <gdk/gdkwayland.h>
 #include <gdk/gdkx.h>
+#endif
 
 #include "flutter/shell/platform/linux/fl_opengl_manager.h"
 

engine/src/flutter/shell/platform/linux/fl_text_input_handler.cc

@@ -347,8 +347,12 @@ static void update_im_cursor_position(FlTextInputHandler* self) {
 
   // Transform from Flutter view coordinates to GTK window coordinates.
   GdkRectangle preedit_rect = {};
-  gtk_widget_translate_coordinates(self->widget,
-                                   gtk_widget_get_toplevel(self->widget), x, y,
+#if FLUTTER_LINUX_GTK4
+  GtkWidget* toplevel = GTK_WIDGET(gtk_widget_get_root(self->widget));
+#else
+  GtkWidget* toplevel = gtk_widget_get_toplevel(self->widget);
+#endif
+  gtk_widget_translate_coordinates(self->widget, toplevel, x, y,
                                    &preedit_rect.x, &preedit_rect.y);
 
   // Set the cursor location in window coordinates so that GTK can position
@@ -480,8 +484,12 @@ void fl_text_input_handler_set_widget(FlTextInputHandler* self,
                                       GtkWidget* widget) {
   g_return_if_fail(FL_IS_TEXT_INPUT_HANDLER(self));
   self->widget = widget;
+#if FLUTTER_LINUX_GTK4
+  gtk_im_context_set_client_widget(self->im_context, widget);
+#else
   gtk_im_context_set_client_window(self->im_context,
                                    gtk_widget_get_window(self->widget));
+#endif
 }
 
 GtkWidget* fl_text_input_handler_get_widget(FlTextInputHandler* self) {

engine/src/flutter/shell/platform/linux/fl_window_state_monitor.cc

@@ -27,7 +27,9 @@ struct _FlWindowStateMonitor {
   GtkWindow* window;
 
   // Current state information.
+#if !FLUTTER_LINUX_GTK4
   GdkWindowState window_state;
+#endif
 
   // Signal connection ID for window-state-changed
   gulong window_state_event_cb_id;
@@ -51,11 +53,13 @@ static void send_lifecycle_state(FlWindowStateMonitor* self,
                                       message, nullptr, nullptr, nullptr);
 }
 
+#if !FLUTTER_LINUX_GTK4
 static gboolean is_hidden(GdkWindowState state) {
   return (state & GDK_WINDOW_STATE_WITHDRAWN) ||
          (state & GDK_WINDOW_STATE_ICONIFIED);
 }
-
+#endif  // !FLUTTER_LINUX_GTK4
+#if !FLUTTER_LINUX_GTK4
 // Signal handler for GtkWindow::window-state-event
 static gboolean window_state_event_cb(FlWindowStateMonitor* self,
                                       GdkEvent* event) {
@@ -81,6 +85,7 @@ static gboolean window_state_event_cb(FlWindowStateMonitor* self,
 
   return FALSE;
 }
+#endif  // !FLUTTER_LINUX_GTK4
 
 static void fl_window_state_monitor_dispose(GObject* object) {
   FlWindowStateMonitor* self = FL_WINDOW_STATE_MONITOR(object);
@@ -109,11 +114,16 @@ FlWindowStateMonitor* fl_window_state_monitor_new(FlBinaryMessenger* messenger,
   self->window = window;
 
   // Listen to window state changes.
+#if !FLUTTER_LINUX_GTK4
   self->window_state_event_cb_id =
       g_signal_connect_swapped(self->window, "window-state-event",
                                G_CALLBACK(window_state_event_cb), self);
   self->window_state =
       gdk_window_get_state(gtk_widget_get_window(GTK_WIDGET(self->window)));
+#else
+  self->window_state_event_cb_id = 0;
+  // TODO(gtk4): Reconnect lifecycle updates using GdkToplevel state.
+#endif
 
   return self;
 }

engine/src/flutter/shell/platform/linux/fl_window_state_monitor_test.cc

@@ -10,6 +10,7 @@
 
 #include "gtest/gtest.h"
 
+#if !FLUTTER_LINUX_GTK4
 TEST(FlWindowStateMonitorTest, GainFocus) {
   g_autoptr(FlMockBinaryMessenger) messenger = fl_mock_binary_messenger_new();
   ::testing::NiceMock<flutter::testing::MockGtk> mock_gtk;
@@ -44,7 +45,6 @@ TEST(FlWindowStateMonitorTest, GainFocus) {
 
   fl_binary_messenger_shutdown(FL_BINARY_MESSENGER(messenger));
 }
-
 TEST(FlWindowStateMonitorTest, LoseFocus) {
   g_autoptr(FlMockBinaryMessenger) messenger = fl_mock_binary_messenger_new();
   ::testing::NiceMock<flutter::testing::MockGtk> mock_gtk;
@@ -287,3 +287,5 @@ TEST(FlWindowStateMonitorTest, LeaveWithdrawnFocused) {
 
   fl_binary_messenger_shutdown(FL_BINARY_MESSENGER(messenger));
 }
+
+#endif  // !FLUTTER_LINUX_GTK4