[gtk+] app: Warn when trying to add windows on an inert instance

[Emmanuele Bassi <ebassi src gnome org>]

commit 707a071c660438235b45ecb66a5610590594b9cb
Author: Emmanuele Bassi <ebassi gnome org>
Date:   Thu Oct 1 18:58:32 2015 +0100

    app: Warn when trying to add windows on an inert instance
    
    Application windows can only be added after the application has been
    started.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=755954

 gtk/gtkapplication.c |   13 ++++++++++++-
 1 files changed, 12 insertions(+), 1 deletions(-)
---
diff --git a/gtk/gtkapplication.c b/gtk/gtkapplication.c
index ba7ef7b..0edfe92 100644
--- a/gtk/gtkapplication.c
+++ b/gtk/gtkapplication.c
@@ -1020,6 +1020,10 @@ gtk_application_new (const gchar       *application_id,
  *
  * Adds a window to @application.
  *
+ * This call can only happen after the @application has started;
+ * typically, you should add new application windows in response
+ * to the emission of the #GApplication::activate signal.
+ *
  * This call is equivalent to setting the #GtkWindow:application
  * property of @window to @application.
  *
@@ -1027,7 +1031,7 @@ gtk_application_new (const gchar       *application_id,
  * will remain until the window is destroyed, but you can explicitly
  * remove it with gtk_application_remove_window().
  *
- * GTK+ will keep the application running as long as it has
+ * GTK+ will keep the @application running as long as it has
  * any windows.
  *
  * Since: 3.0
@@ -1038,6 +1042,13 @@ gtk_application_add_window (GtkApplication *application,
 {
   g_return_if_fail (GTK_IS_APPLICATION (application));
 
+  if (!g_application_get_is_registered (G_APPLICATION (application)))
+    {
+      g_critical ("New application windows must be added after the "
+                  "GApplication::startup signal has been emitted.");
+      return;
+    }
+
   if (!g_list_find (application->priv->windows, window))
     g_signal_emit (application,
                    gtk_application_signals[WINDOW_ADDED], 0, window);