wayland-keyboard: Don't send pressed keys on enter

We never want to send pressed keys to wayland clients on enter. The
protocol says that we should send them, presumably so that clients can
trigger their own key repeat routine in case they are given focus and
a key is physically pressed.

Unfortunately this causes some clients, in particular Xwayland, to
register key events that they really shouldn't handle, e.g. on an
Alt+Tab keybinding, where Alt is released before Tab, clients would
see Tab being pressed on enter followed by a key release event for
Tab, meaning that Tab would be processed by the client when it really
shouldn't.

Since the use case for the pressed keys array on enter seems weak to
us, we'll just fake that there are no pressed keys instead which
should be spec compliant even if it might not be true.

https://bugzilla.gnome.org/show_bug.cgi?id=727178

src/wayland/meta-wayland-keyboard.c

@@ -383,8 +383,6 @@ meta_wayland_keyboard_init (MetaWaylandKeyboard *keyboard,
 
   keyboard->focus_surface_listener.notify = keyboard_handle_focus_surface_destroy;
 
-  wl_array_init (&keyboard->pressed_keys);
-
   keyboard->xkb_info.keymap_fd = -1;
 
   keyboard->settings = g_settings_new ("org.gnome.settings-daemon.peripherals.keyboard");
@@ -417,47 +415,12 @@ meta_wayland_keyboard_release (MetaWaylandKeyboard *keyboard)
   meta_wayland_xkb_info_destroy (&keyboard->xkb_info);
 
   /* XXX: What about keyboard->resource_list? */
-  wl_array_release (&keyboard->pressed_keys);
 
   g_object_unref (keyboard->settings);
 
   keyboard->display = NULL;
 }
 
-static void
-update_pressed_keys (struct wl_array *keys,
-                     uint32_t         evdev_code,
-                     gboolean         is_press)
-{
-  uint32_t *end = (void *) ((char *) keys->data + keys->size);
-  uint32_t *k;
-
-  if (is_press)
-    {
-      /* Make sure we don't already have this key. */
-      for (k = keys->data; k < end; k++)
-        if (*k == evdev_code)
-          return;
-
-      /* Otherwise add the key to the list of pressed keys */
-      k = wl_array_add (keys, sizeof (*k));
-      *k = evdev_code;
-    }
-  else
-    {
-      /* Remove the key from the array */
-      for (k = keys->data; k < end; k++)
-        if (*k == evdev_code)
-          {
-            *k = *(end - 1);
-            keys->size -= sizeof (*k);
-            return;
-          }
-
-      g_warning ("unexpected key release event for key 0x%x", evdev_code);
-    }
-}
-
 static guint
 evdev_code (const ClutterKeyEvent *event)
 {
@@ -474,8 +437,6 @@ meta_wayland_keyboard_update (MetaWaylandKeyboard *keyboard,
   struct xkb_state *state = keyboard->xkb_info.state;
   enum xkb_state_component changed_state;
 
-  update_pressed_keys (&keyboard->pressed_keys, evdev_code (event), is_press);
-
   changed_state = xkb_state_update_key (state,
                                         event->hardware_keycode,
                                         is_press ? XKB_KEY_DOWN : XKB_KEY_UP);
@@ -538,8 +499,27 @@ static void
 broadcast_focus (MetaWaylandKeyboard *keyboard,
                  struct wl_resource  *resource)
 {
+  struct wl_array fake_keys;
   struct xkb_state *state = keyboard->xkb_info.state;
 
+  /* We never want to send pressed keys to wayland clients on
+   * enter. The protocol says that we should send them, presumably so
+   * that clients can trigger their own key repeat routine in case
+   * they are given focus and a key is physically pressed.
+   *
+   * Unfortunately this causes some clients, in particular Xwayland,
+   * to register key events that they really shouldn't handle,
+   * e.g. on an Alt+Tab keybinding, where Alt is released before Tab,
+   * clients would see Tab being pressed on enter followed by a key
+   * release event for Tab, meaning that Tab would be processed by
+   * the client when it really shouldn't.
+   *
+   * Since the use case for the pressed keys array on enter seems weak
+   * to us, we'll just fake that there are no pressed keys instead
+   * which should be spec compliant even if it might not be true.
+   */
+  wl_array_init (&fake_keys);
+
   wl_keyboard_send_modifiers (resource, keyboard->focus_serial,
                               xkb_state_serialize_mods (state, XKB_STATE_MODS_DEPRESSED),
                               xkb_state_serialize_mods (state, XKB_STATE_MODS_LATCHED),
@@ -547,7 +527,7 @@ broadcast_focus (MetaWaylandKeyboard *keyboard,
                               xkb_state_serialize_layout (state, XKB_STATE_LAYOUT_EFFECTIVE));
   wl_keyboard_send_enter (resource, keyboard->focus_serial,
                           keyboard->focus_surface->resource,
-                          &keyboard->pressed_keys);
+                          &fake_keys);
 }
 
 void

src/wayland/meta-wayland-keyboard.h

@@ -69,8 +69,6 @@ struct _MetaWaylandKeyboard
   struct wl_listener focus_surface_listener;
   uint32_t focus_serial;
 
-  struct wl_array pressed_keys;
-
   MetaWaylandXkbInfo xkb_info;
 
   GSettings *settings;