startup-notification/x11: Let the libsn user handle API annoyances

The API has no concept of user data, and requires the user to some how
get an instance without context, i.e. via static globals. Limit this to
the file where this is needed.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2718>

src/core/display-private.h

@@ -298,8 +298,6 @@ META_EXPORT_TEST
 GSList*     meta_display_list_windows        (MetaDisplay          *display,
                                               MetaListWindowsFlags  flags);
 
-MetaDisplay* meta_display_for_x_display  (Display     *xdisplay);
-
 META_EXPORT_TEST
 MetaDisplay* meta_get_display            (void);
 

src/core/display.c

@@ -1205,31 +1205,6 @@ meta_display_close (MetaDisplay *display,
   the_display = NULL;
 }
 
-/**
- * meta_display_for_x_display:
- * @xdisplay: An X display
- *
- * Returns the singleton MetaDisplay if @xdisplay matches the X display it's
- * managing; otherwise gives a warning and returns %NULL.  When we were claiming
- * to be able to manage multiple displays, this was supposed to find the
- * display out of the list which matched that display.  Now it's merely an
- * extra sanity check.
- *
- * Returns: The singleton X display, or %NULL if @xdisplay isn't the one
- *          we're managing.
- */
-MetaDisplay*
-meta_display_for_x_display (Display *xdisplay)
-{
-  if (the_display->x11_display->xdisplay == xdisplay)
-    return the_display;
-
-  meta_warning ("Could not find display for X display %p, probably going to crash",
-                xdisplay);
-
-  return NULL;
-}
-
 /**
  * meta_get_display:
  *

src/x11/meta-startup-notification-x11.c

@@ -51,6 +51,8 @@ struct _MetaX11StartupNotification
 
 static GParamSpec *seq_x11_props[N_SEQ_X11_PROPS];
 
+static GList *displays;
+
 G_DEFINE_TYPE (MetaStartupSequenceX11,
                meta_startup_sequence_x11,
                META_TYPE_STARTUP_SEQUENCE)
@@ -168,13 +170,36 @@ meta_startup_sequence_x11_new (MetaDisplay       *display,
                        NULL);
 }
 
+static MetaDisplay *
+find_display (Display *xdisplay)
+{
+  GList *l;
+
+  for (l = displays; l; l = l->next)
+    {
+      MetaDisplay *display = l->data;
+      MetaX11Display *x11_display;
+
+      x11_display = display->x11_display;
+      if (!x11_display)
+        continue;
+
+      if (x11_display->xdisplay != xdisplay)
+        continue;
+
+      return display;
+    }
+
+  return NULL;
+}
+
 static void
 sn_error_trap_push (SnDisplay *sn_display,
                     Display   *xdisplay)
 {
   MetaDisplay *display;
 
-  display = meta_display_for_x_display (xdisplay);
+  display = find_display (xdisplay);
   if (display != NULL)
     meta_x11_error_trap_push (display->x11_display);
 }
@@ -185,7 +210,7 @@ sn_error_trap_pop (SnDisplay *sn_display,
 {
   MetaDisplay *display;
 
-  display = meta_display_for_x_display (xdisplay);
+  display = find_display (xdisplay);
   if (display != NULL)
     meta_x11_error_trap_pop (display->x11_display);
 }
@@ -253,13 +278,21 @@ meta_startup_notification_sn_event (SnMonitorEvent *event,
 
   sn_startup_sequence_unref (sequence);
 }
-#endif
+
+static void
+on_x11_display_closing (MetaDisplay *display)
+{
+  g_signal_handlers_disconnect_by_func (display, on_x11_display_closing, NULL);
+  displays = g_list_remove (displays, display);
+}
+#endif /* HAVE_STARTUP_NOTIFICATION */
 
 void
 meta_x11_startup_notification_init (MetaX11Display *x11_display)
 {
 #ifdef HAVE_STARTUP_NOTIFICATION
   MetaX11StartupNotification *x11_sn;
+  MetaDisplay *display;
 
   x11_sn = g_new0 (MetaX11StartupNotification, 1);
   x11_sn->sn_display = sn_display_new (x11_display->xdisplay,
@@ -273,6 +306,14 @@ meta_x11_startup_notification_init (MetaX11Display *x11_display)
                             NULL);
 
   x11_display->startup_notification = x11_sn;
+
+  display = meta_x11_display_get_display (x11_display);
+  if (!g_list_find (displays, display))
+    {
+      displays = g_list_prepend (displays, display);
+      g_signal_connect (display, "x11-display-closing",
+                        G_CALLBACK (on_x11_display_closing), NULL);
+    }
 #endif
 }