gtkwidget: better handle when trying to focus a widget with no GtkRoot

Issue #5676 found a case where GTK tried to focus a widget with
a NULL GtkRoot. That specific case was a GtkButton which was a
GtkExpander's child, and until the GtkExpander is expanded (and
thus the GtkButton becomes visible) the button has no GtkRoot,
yet GTK tried to focus on it when GtkExpander's code called
gtk_widget_focus_child() on it.

We could change GtkExpander code to check if widget has no GtkRoot
and in that case avoid calling gtk_widget_focus_child(), but
it seems generally better to handle this at GtkWidget level so
it may cover other widgets that could misbehave in a similar way
as GtkExpander.

So in this patch:

We turn a critical message (failed assertion) into a proper warning
which informs the user about the non-allowed action.

We also make sure gtk_widget_focus_child() properly returns FALSE
when called on an unrooted widget.

Fixes #5676

gtk/gtkurilauncher.c

@@ -213,64 +213,20 @@ gtk_uri_launcher_set_uri (GtkUriLauncher *self,
 /* {{{ Async implementation */
 
 #ifndef G_OS_WIN32
-static void show_uri_done (GObject      *source,
-                           GAsyncResult *result,
-                           gpointer      data);
-
-typedef struct {
-  GtkUriLauncher *launcher;
-  GtkWindow *window;
-  GCancellable *cancellable;
-  GTask *task;
-  GAsyncReadyCallback orig_callback;
-  gpointer orig_callback_data;
-} CallbackData;
-
-static void
-free_callback_data (CallbackData *data)
-{
-  g_clear_object (&data->launcher);
-  g_clear_object (&data->task);
-  g_clear_object (&data->window);
-  g_clear_object (&data->cancellable);
-  g_free (data);
-}
-
-static gboolean
-show_uri_in_idle (CallbackData *cbdata)
-{
-G_GNUC_BEGIN_IGNORE_DEPRECATIONS
-  gtk_show_uri_full (cbdata->window, cbdata->launcher->uri, GDK_CURRENT_TIME,
-                     cbdata->cancellable, show_uri_done, cbdata->task);
-G_GNUC_END_IGNORE_DEPRECATIONS
-  free_callback_data (cbdata);
-
-  return FALSE;
-}
-
 static void
 open_done (GObject      *source,
            GAsyncResult *result,
            gpointer      data)
 {
-  CallbackData *cbdata = (CallbackData *) data;
+  GTask *task = G_TASK (data);
   GError *error = NULL;
 
-  if (!gtk_openuri_portal_open_uri_finish (result, &error)) {
-    /* DBus method failed or is not implemented,
-     * try again without using portal - Issue #5733 */
-    GTask *task;
-    task = g_task_new (cbdata->launcher, cbdata->cancellable,
-                       cbdata->orig_callback, cbdata->orig_callback_data);
-    g_task_set_check_cancellable (task, FALSE);
-    g_task_set_source_tag (task, open_done);
-    g_clear_object (&cbdata->task);
-    cbdata->task = g_object_ref (task);
-    g_idle_add (G_SOURCE_FUNC (show_uri_in_idle), cbdata);
-  } else {
-    g_task_return_boolean (cbdata->task, TRUE);
-    free_callback_data (cbdata);
-  }
+  if (!gtk_openuri_portal_open_uri_finish (result, &error))
+    g_task_return_error (task, error);
+  else
+    g_task_return_boolean (task, TRUE);
+
+  g_object_unref (task);
 }
 #endif
 
@@ -344,19 +300,9 @@ gtk_uri_launcher_launch (GtkUriLauncher     *self,
     }
 
 #ifndef G_OS_WIN32
-  if (gtk_openuri_portal_is_available ()) {
-    CallbackData *callback_data;
-
-    callback_data = g_new (CallbackData, 1);
-    callback_data->launcher = g_object_ref (self);
-    callback_data->task = g_object_ref (task);
-    callback_data->window =  parent ? g_object_ref (parent) : NULL;
-    callback_data->cancellable = cancellable ? g_object_ref (cancellable) : NULL;
-    callback_data->orig_callback = callback;
-    callback_data->orig_callback_data = user_data;
-
-    gtk_openuri_portal_open_uri_async (self->uri, parent, cancellable, open_done, callback_data);
-  } else
+  if (gtk_openuri_portal_is_available ())
+    gtk_openuri_portal_open_uri_async (self->uri, parent, cancellable, open_done, task);
+  else
 #endif
 G_GNUC_BEGIN_IGNORE_DEPRECATIONS
     gtk_show_uri_full (parent, self->uri, GDK_CURRENT_TIME, cancellable, show_uri_done, task);

gtk/gtkwidget.c

@@ -5020,6 +5020,7 @@ gtk_widget_real_focus (GtkWidget        *widget,
                        GtkDirectionType  direction)
 {
   GtkWidget *focus;
+  GtkRoot *root;
 
   /* For focusable widgets, we want to focus the widget
    * before its children. We differentiate 3 cases:
@@ -5037,7 +5038,12 @@ gtk_widget_real_focus (GtkWidget        *widget,
       return FALSE;
     }
 
-  focus = gtk_window_get_focus (GTK_WINDOW (gtk_widget_get_root (widget)));
+  root = gtk_widget_get_root (widget);
+  if (!root) {
+    g_warning ("Attempted to focus a widget with no GtkRoot");
+    return FALSE;
+  }
+  focus = gtk_window_get_focus (GTK_WINDOW (root));
 
   if (focus && gtk_widget_is_ancestor (focus, widget))
     {
@@ -6883,7 +6889,8 @@ gtk_widget_child_focus (GtkWidget       *widget,
 
   if (!_gtk_widget_get_visible (widget) ||
       !gtk_widget_is_sensitive (widget) ||
-      !gtk_widget_get_can_focus (widget))
+      !gtk_widget_get_can_focus (widget)||
+      !gtk_widget_get_root (widget))
     return FALSE;
 
   /* Emit ::focus in any case, even if focusable is FALSE,