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

Back in 2014 sending pressed keys to Wayland clients caused issues,
because at least Xwayland didn't handle that gracefully, causing issues
like ghost-pressed keys. A way it was reproduced was quickly alt-tab:ing
to and from a Firefox window, which would cause the File menu bar
incorrectly appearing.

While this was reported to the Xwayland component back then, it was,
probably by mistake, assumed to be an issue in mutter, and mutter
stopped sending pressed key events on enter.

The following year, Xwayland was eventually fixed, but the work around
in mutter has been kept around until it was again noticed as an
inconsistency between compositor implementations.

Lets remove the work around, and follow the spec, again.

This reverts commit c39f18c2d438efe3a866767c9546a6140dd5aaad.

Closes: https://gitlab.gnome.org/GNOME/mutter/-/issues/2457
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2657>

2 files changed, 48 insertions, 21 deletions

diff --git a/src/wayland/meta-wayland-keyboard.c b/src/wayland/meta-wayland-keyboard.c
index b6dbab3b8..a243b51a1 100644
--- a/src/wayland/meta-wayland-keyboard.c
+++ b/src/wayland/meta-wayland-keyboard.c
@@ -514,6 +514,9 @@ meta_wayland_keyboard_enable (MetaWaylandKeyboard *keyboard)
   ClutterBackend *clutter_backend = clutter_get_default_backend ();
 
   keyboard->settings = g_settings_new ("org.gnome.desktop.peripherals.keyboard");
+
+  wl_array_init (&keyboard->pressed_keys);
+
   g_signal_connect (keyboard->settings, "changed",
                     G_CALLBACK (settings_changed), keyboard);
 
@@ -553,9 +556,49 @@ meta_wayland_keyboard_disable (MetaWaylandKeyboard *keyboard)
   wl_list_remove (&keyboard->focus_resource_list);
   wl_list_init (&keyboard->focus_resource_list);
 
+  wl_array_release (&keyboard->pressed_keys);
+
   g_clear_object (&keyboard->settings);
 }
 
+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);
+    }
+}
+
 void
 meta_wayland_keyboard_update (MetaWaylandKeyboard *keyboard,
                               const ClutterKeyEvent *event)
@@ -570,6 +613,8 @@ meta_wayland_keyboard_update (MetaWaylandKeyboard *keyboard,
        (CLUTTER_EVENT_FLAG_SYNTHETIC | CLUTTER_EVENT_FLAG_INPUT_METHOD)) != 0)
     return;
 
+  update_pressed_keys (&keyboard->pressed_keys, event->evdev_code, is_press);
+
   /* If we get a key event but still have pending modifier state
    * changes from a previous event that didn't get cleared, we need to
    * send that state right away so that the new key event can be
@@ -674,30 +719,10 @@ static void
 broadcast_focus (MetaWaylandKeyboard *keyboard,
                  struct wl_resource  *resource)
 {
-  struct wl_array fake_keys;
-
-  /* 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);
-
   keyboard_send_modifiers (keyboard, resource, keyboard->focus_serial);
   wl_keyboard_send_enter (resource, keyboard->focus_serial,
                           keyboard->focus_surface->resource,
-                          &fake_keys);
+                          &keyboard->pressed_keys);
 }
 
 void
diff --git a/src/wayland/meta-wayland-keyboard.h b/src/wayland/meta-wayland-keyboard.h
index 6cce803ff..5e761cde9 100644
--- a/src/wayland/meta-wayland-keyboard.h
+++ b/src/wayland/meta-wayland-keyboard.h
@@ -95,6 +95,8 @@ struct _MetaWaylandKeyboard
   uint32_t key_up_keycode;
   uint32_t key_up_serial;
 
+  struct wl_array pressed_keys;
+
   MetaWaylandXkbInfo xkb_info;
   enum xkb_state_component mods_changed;
   xkb_mod_mask_t kbd_a11y_latched_mods;