Disable Qt's integration mechanism on GTK-based DE to avoid early GTK loading

This also removes TDESKTOP_USE_GTK_FILE_DIALOG since it doesn't forces GTK dialog for anyone and there is no reason to leave it

TDESKTOP_DISABLE_GTK_INTEGRATION can be also tested via action now

Telegram/SourceFiles/platform/linux/file_utilities_linux.cpp

@@ -130,11 +130,12 @@ bool NativeSupported(Type type = Type::ReadFile) {
 	// or if QT_QPA_PLATFORMTHEME=(gtk2|gtk3)
 	// or if portals is used and operation is to open folder
 	// and portal doesn't support folder choosing
-	return Platform::UseGtkFileDialog()
-		&& (Platform::DesktopEnvironment::IsGtkBased()
+	return (Platform::DesktopEnvironment::IsGtkBased()
 			|| Platform::IsGtkIntegrationForced()
 			|| Platform::UseXDGDesktopPortal())
-		&& (!Platform::UseXDGDesktopPortal()
+		&& ((!Platform::UseXDGDesktopPortal() &&
+			((!Platform::InFlatpak() && !Platform::InSnap())
+				|| Platform::IsGtkIntegrationForced()))
 			|| (type == Type::ReadFolder && !Platform::CanOpenDirectoryWithPortal()))
 		&& Platform::internal::GdkHelperLoaded()
 		&& (Libs::gtk_widget_hide_on_delete != nullptr)

Telegram/SourceFiles/platform/linux/linux_libs.cpp

@@ -7,6 +7,7 @@ https://github.com/telegramdesktop/tdesktop/blob/master/LEGAL
 */
 #include "platform/linux/linux_libs.h"
 
+#include "base/platform/base_platform_info.h"
 #include "platform/linux/linux_xlib_helper.h"
 #include "platform/linux/linux_gdk_helper.h"
 #include "platform/linux/specific_linux.h"
@@ -114,8 +115,13 @@ bool setupGtkBase(QLibrary &lib_gtk) {
 		// Otherwise we get segfault in Ubuntu 17.04 in gtk_init_check() call.
 		// See https://github.com/telegramdesktop/tdesktop/issues/3176
 		// See https://github.com/telegramdesktop/tdesktop/issues/3162
-		DEBUG_LOG(("Limit allowed GDK backends to wayland and x11"));
-		gdk_set_allowed_backends("wayland,x11");
+		if(Platform::IsWayland()) {
+			DEBUG_LOG(("Limit allowed GDK backends to wayland,x11"));
+			gdk_set_allowed_backends("wayland,x11");
+		} else {
+			DEBUG_LOG(("Limit allowed GDK backends to x11,wayland"));
+			gdk_set_allowed_backends("x11,wayland");
+		}
 	}
 
 	// gtk_init will reset the Xlib error handler, and that causes

Telegram/SourceFiles/platform/linux/specific_linux.cpp

@@ -682,14 +682,6 @@ bool IsGtkIntegrationForced() {
 	return false;
 }
 
-bool UseGtkFileDialog() {
-#ifdef TDESKTOP_USE_GTK_FILE_DIALOG
-	return true;
-#else // TDESKTOP_USE_GTK_FILE_DIALOG
-	return false;
-#endif // !TDESKTOP_USE_GTK_FILE_DIALOG
-}
-
 bool IsQtPluginsBundled() {
 #ifdef DESKTOP_APP_USE_PACKAGED_LAZY
 	return true;
@@ -1210,6 +1202,11 @@ void start() {
 
 		qunsetenv("QT_QPA_PLATFORMTHEME");
 		qunsetenv("QT_STYLE_OVERRIDE");
+
+		// Don't allow qgtk3 to init gtk earlier than us
+		if (DesktopEnvironment::IsGtkBased()) {
+			QApplication::setDesktopSettingsAware(false);
+		}
 	}
 
 	if (!UseGtkIntegration()) {
@@ -1241,10 +1238,10 @@ void start() {
 
 	if((IsStaticBinary()
 		|| InAppImage()
-		|| InSnap()
-		|| UseGtkFileDialog()
 		|| IsQtPluginsBundled())
-		&& !InFlatpak()) {
+		// it is handled by Qt for flatpak and snap
+		&& !InFlatpak()
+		&& !InSnap()) {
 		LOG(("Checking for XDG Desktop Portal..."));
 		// this can give us a chance to use
 		// a proper file dialog for current session

Telegram/SourceFiles/platform/linux/specific_linux.h

@@ -26,7 +26,6 @@ bool InAppImage();
 bool IsStaticBinary();
 bool UseGtkIntegration();
 bool IsGtkIntegrationForced();
-bool UseGtkFileDialog();
 bool IsQtPluginsBundled();
 
 bool IsXDGDesktopPortalPresent();