Fix a crash on exit on macOS

Calling Python API functions is not allowed in atexit handlers.

Fixes #3686

docs/changelog.rst

@@ -76,6 +76,8 @@ To update |kitty|, :doc:`follow the instructions <binary>`.
 - Fix a regression that caused using the ``title`` command in session files
   to stop working (:iss:`3676`)
 
+- macOS: Fix a rare crash on exit (:iss:`3686`)
+
 
 0.20.3 [2021-05-06]
 ----------------------

kitty/cocoa_window.m

@@ -160,9 +160,11 @@ static PyObject *notification_activated_callback = NULL;
 
 static PyObject*
 set_notification_activated_callback(PyObject *self UNUSED, PyObject *callback) {
-    if (notification_activated_callback) Py_DECREF(notification_activated_callback);
-    notification_activated_callback = callback;
-    Py_INCREF(callback);
+    Py_CLEAR(notification_activated_callback);
+    if (callback != Py_None)
+        notification_activated_callback = callback;
+        Py_INCREF(callback);
+    }
     Py_RETURN_NONE;
 }
 
@@ -638,7 +640,6 @@ cleanup() {
 
     if (dockMenu) [dockMenu release];
     dockMenu = nil;
-    Py_CLEAR(notification_activated_callback);
 
 #ifndef KITTY_USE_DEPRECATED_MACOS_NOTIFICATION_API
     drain_pending_notifications(NO);

kitty/fast_data_types.pyi

@@ -1182,3 +1182,7 @@ def click_mouse_url(os_window_id: int, tab_id: int, window_id: int) -> None:
 
 def mouse_selection(os_window_id: int, tab_id: int, window_id: int, code: int, button: int) -> None:
     pass
+
+
+def set_notification_activated_callback(cb: Optional[Callable]) -> None:
+    pass

kitty/main.py

@@ -178,6 +178,9 @@ class AppRunner:
         finally:
             set_options(None)
             free_font_data()  # must free font data before glfw/freetype/fontconfig/opengl etc are finalized
+            if is_macos:
+                from kitty.fast_data_types import set_notification_activated_callback
+                set_notification_activated_callback(None)
 
 
 run_app = AppRunner()