tests/stacking: Add test hiding a modal with a not shown parent

This adds a test case for
https://gitlab.gnome.org/GNOME/mutter/-/issues/862 that checks that
hiding a dialog where its parent is not yet shown doesn't trigger any
asserts or crashes.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1643>

src/tests/meson.build

@@ -179,6 +179,7 @@ stacking_tests = [
   'fullscreen-maximize',
   'restore-position',
   'default-size',
+  'modals',
 ]
 
 foreach stacking_test: stacking_tests

src/tests/stacking/modals.metatest

@@ -0,0 +1,32 @@
+new_client w wayland
+
+# Create two Wayland windows, and make the second a transient of the
+# first. Then make the parent not actually ever show, but show the
+# transient.
+
+# Then make sure that hiding the transient can hide without causing
+# issues.
+
+# https://gitlab.gnome.org/GNOME/mutter/-/issues/862
+
+create w/1 csd
+create w/2 csd
+
+set_parent w/2 1
+
+freeze w/1
+
+show w/1 async
+show w/2
+
+wait
+
+assert_stacking w/1 w/2
+
+hide w/2
+wait
+
+assert_stacking w/1
+
+hide w/2
+wait

src/tests/test-client.c

@@ -766,6 +766,34 @@ process_line (const char *line)
 
       gtk_window_unfullscreen (GTK_WINDOW (window));
     }
+  else if (strcmp (argv[0], "freeze") == 0)
+    {
+      if (argc != 2)
+        {
+          g_print ("usage: freeze <id>\n");
+          goto out;
+        }
+
+      GtkWidget *window = lookup_window (argv[1]);
+      if (!window)
+        goto out;
+
+      gdk_window_freeze_updates (gtk_widget_get_window (window));
+    }
+  else if (strcmp (argv[0], "thaw") == 0)
+    {
+      if (argc != 2)
+        {
+          g_print ("usage: thaw <id>\n");
+          goto out;
+        }
+
+      GtkWidget *window = lookup_window (argv[1]);
+      if (!window)
+        goto out;
+
+      gdk_window_thaw_updates (gtk_widget_get_window (window));
+    }
   else if (strcmp (argv[0], "assert_size") == 0)
     {
       int expected_width;

src/tests/test-runner.c

@@ -561,8 +561,13 @@ test_case_do (TestCase *test,
     }
   else if (strcmp (argv[0], "show") == 0)
     {
-      if (argc != 2)
-        BAD_COMMAND("usage: %s <client-id>/<window-id>", argv[0]);
+      gboolean show_async = FALSE;
+
+      if (argc != 2 && argc != 3)
+        BAD_COMMAND("usage: %s <client-id>/<window-id> [async]", argv[0]);
+
+      if (argc == 3 && strcmp (argv[2], "async") == 0)
+        show_async = TRUE;
 
       TestClient *client;
       const char *window_id;
@@ -579,7 +584,8 @@ test_case_do (TestCase *test,
       if (!window)
         return FALSE;
 
-      test_client_wait_for_window_shown (client, window);
+      if (!show_async)
+        test_client_wait_for_window_shown (client, window);
     }
   else if (strcmp (argv[0], "resize") == 0)
     {
@@ -671,6 +677,8 @@ test_case_do (TestCase *test,
            strcmp (argv[0], "unmaximize") == 0 ||
            strcmp (argv[0], "fullscreen") == 0 ||
            strcmp (argv[0], "unfullscreen") == 0 ||
+           strcmp (argv[0], "freeze") == 0 ||
+           strcmp (argv[0], "thaw") == 0 ||
            strcmp (argv[0], "destroy") == 0)
     {
       if (argc != 2)