core: preserve focus across decoration changes

Changes in window decoration result in the window being reparented
in and out its frame. This in turn causes unmap/map events, and
FocusOut if the window happened to be focused.

In order to preserve the focused window across the decoration change,
add a flag so that the focus may be restored on MapNotify.

Based on mutter commit:
https://gitlab.gnome.org/GNOME/mutter/commit/8dcac664faf03ac2ea382e

4 files changed, 23 insertions, 0 deletions

diff --git a/src/core/display.c b/src/core/display.c
index 555543f8..c43ed3d4 100644
--- a/src/core/display.c
+++ b/src/core/display.c
@@ -2352,6 +2352,11 @@ event_callback (XEvent   *event,
           window = meta_window_new (display, event->xmap.window, FALSE,
                                     META_EFFECT_TYPE_CREATE);
         }
+      else if (window && window->restore_focus_on_map)
+        {
+          meta_window_focus (window,
+                             meta_display_get_current_time_roundtrip (display));
+        }
       break;
     case MapRequest:
       if (window == NULL)
diff --git a/src/core/frame.c b/src/core/frame.c
index e804775d..c166b865 100644
--- a/src/core/frame.c
+++ b/src/core/frame.c
@@ -146,6 +146,12 @@ meta_window_ensure_frame (MetaWindow *window)
   /* FIXME handle this error */
   meta_error_trap_pop (window->display);
 
+  /* Ensure focus is restored after the unmap/map events triggered
+   * by XReparentWindow().
+   */
+  if (meta_window_has_focus (window))
+    window->restore_focus_on_map = TRUE;
+
   /* stick frame to the window */
   window->frame = frame;
 
@@ -216,6 +222,12 @@ meta_window_destroy_frame (MetaWindow *window)
 
   meta_ui_destroy_frame_window (window->screen->ui, frame->xwindow);
 
+  /* Ensure focus is restored after the unmap/map events triggered
+   * by XReparentWindow().
+   */
+  if (meta_window_has_focus (window))
+    window->restore_focus_on_map = TRUE;
+
   meta_display_unregister_x_window (window->display,
                                     frame->xwindow);
 
diff --git a/src/core/window-private.h b/src/core/window-private.h
index 7f7eb276..cc99b7a1 100644
--- a/src/core/window-private.h
+++ b/src/core/window-private.h
@@ -341,6 +341,9 @@ struct _MetaWindow
   /* if TRUE, we are freezing updates during a resize */
   guint updates_frozen_for_resize : 1;
 
+  /* whether focus should be restored on map */
+  guint restore_focus_on_map : 1;
+
   /* if non-NULL, the bounds of the window frame */
   cairo_region_t *frame_bounds;
 
diff --git a/src/core/window.c b/src/core/window.c
index bdb2512e..53ccf86c 100644
--- a/src/core/window.c
+++ b/src/core/window.c
@@ -4499,6 +4499,9 @@ meta_window_focus (MetaWindow  *window,
 
   g_return_if_fail (!window->override_redirect);
 
+  /* This is a oneshot flag */
+  window->restore_focus_on_map = FALSE;
+
   meta_topic (META_DEBUG_FOCUS,
               "Setting input focus to window %s, input: %d take_focus: %d\n",
               window->desc, window->input, window->take_focus);