[mutter] Improve handling of tracking the old focused window during restart

[Owen Taylor <otaylor src gnome org>]

commit b112d982781f9f3618784ddce03c0163ebac54db
Author: Owen W. Taylor <otaylor fishsoup net>
Date:   Tue May 10 17:36:51 2016 -0400

    Improve handling of tracking the old focused window during restart
    
    When restarting (X compositor only, obviously), we want to keep
    the same window focused. There is code that tries to do this by
    calling XGetInputFocus() but the previously focused window will
    almost certainly not still be focused by the time we get to the
    point where we call XGetInputFocus(), and in fact, probably was
    no longer correct after the previous window manager exited, so
    the net result is that we tend to focus no window on restart.
    
    A better approach is to leave the _NET_ACTIVE_WINDOW property
    set on the root window during exit, and if we find it set when
    starting, use that to initialize focus.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=766243

 src/core/display.c |   56 +++++++++++++++++----------------------------------
 1 files changed, 19 insertions(+), 37 deletions(-)
---
diff --git a/src/core/display.c b/src/core/display.c
index a0a4b36..c047297 100644
--- a/src/core/display.c
+++ b/src/core/display.c
@@ -546,6 +546,7 @@ meta_display_open (void)
   MetaScreen *screen;
   int i;
   guint32 timestamp;
+  Window old_active_xwindow = None;
 
   /* A list of all atom names, so that we can intern them in one go. */
   const char *atom_names[] = {
@@ -911,6 +912,11 @@ meta_display_open (void)
 
   display->screen = screen;
 
+  if (!meta_is_wayland_compositor ())
+    meta_prop_get_window (display, display->screen->xroot,
+                          display->atom__NET_ACTIVE_WINDOW,
+                          &old_active_xwindow);
+
   display->startup_notification = meta_startup_notification_get (display);
   g_signal_connect (display->startup_notification, "changed",
                     G_CALLBACK (on_startup_notification_changed), display);
@@ -932,43 +938,16 @@ meta_display_open (void)
   if (!meta_is_wayland_compositor ())
     meta_screen_manage_all_windows (screen);
 
-  {
-    Window focus;
-    int ret_to;
-
-    /* kinda bogus because GetInputFocus has no possible errors */
-    meta_error_trap_push (display);
-
-    /* FIXME: This is totally broken; see comment 9 of bug 88194 about this */
-    focus = None;
-    ret_to = RevertToPointerRoot;
-    XGetInputFocus (display->xdisplay, &focus, &ret_to);
-
-    /* Force a new FocusIn (does this work?) */
-
-    /* Use the same timestamp that was passed to meta_screen_new(),
-     * as it is the most recent timestamp.
-     */
-    if (focus == None || focus == PointerRoot)
-      /* Just focus the no_focus_window on the first screen */
-      meta_display_focus_the_no_focus_window (display,
-                                              display->screen,
-                                              timestamp);
-    else
-      {
-        MetaWindow * window;
-        window  = meta_display_lookup_x_window (display, focus);
-        if (window)
-          meta_display_set_input_focus_window (display, window, FALSE, timestamp);
-        else
-          /* Just focus the no_focus_window on the first screen */
-          meta_display_focus_the_no_focus_window (display,
-                                                  display->screen,
-                                                  timestamp);
-      }
-
-    meta_error_trap_pop (display);
-  }
+  if (old_active_xwindow != None)
+    {
+      MetaWindow *old_active_window = meta_display_lookup_x_window (display, old_active_xwindow);
+      if (old_active_window)
+        meta_window_focus (old_active_window, timestamp);
+      else
+        meta_display_focus_the_no_focus_window (display, display->screen, timestamp);
+    }
+  else
+    meta_display_focus_the_no_focus_window (display, display->screen, timestamp);
 
   meta_idle_monitor_init_dbus ();
 
@@ -2062,6 +2041,9 @@ meta_display_update_active_window_hint (MetaDisplay *display)
 {
   gulong data[1];
 
+  if (display->closing)
+    return; /* Leave old value for a replacement */
+
   if (display->focus_window)
     data[0] = display->focus_window->xwindow;
   else