keyboard: make keybind match stricter

...and avoid failing to send release events to clients for any keys that were
not absorbed by a keybind.

Do not match keybinds if there are other non-modifier keys (not part of any
defined bind) pressed at the same time.

Only store non-modifier keycodes in the key-state.c 'pressed' array.
This makes the call to wlr_seat_keyboard_notify_enter() in seat_focus()
consistent with the equivalent in sway (in seat_keyboard_notify_enter()).

Fixes: issue #1091

include/key-state.h

@@ -21,5 +21,6 @@ void key_state_store_pressed_keys_as_bound(void);
 bool key_state_corresponding_press_event_was_bound(uint32_t keycode);
 void key_state_bound_key_remove(uint32_t keycode);
 int key_state_nr_keys(void);
+int key_state_nr_pressed_keys(void);
 
 #endif /* LABWC_KEY_STATE_H */

src/key-state.c

@@ -102,3 +102,9 @@ key_state_nr_keys(void)
 {
 	return bound.nr_keys;
 }
+
+int
+key_state_nr_pressed_keys(void)
+{
+	return pressed.nr_keys;
+}

src/keyboard.c

@@ -203,8 +203,34 @@ handle_compositor_keybindings(struct keyboard *keyboard,
 
 	bool handled = false;
 
+	/*
+	 * keyboard_key_notify() is called before keyboard_key_modifier(), so
+	 * 'modifiers' refers to modifiers that were pressed before the key
+	 * event in hand. Consequently, we use is_modifier_key() to find out if
+	 * the key event being processed is a modifier.
+	 *
+	 * Sway solves this differently by saving the 'modifiers' state and
+	 * checking if it has changed each time we get to the equivalent of this
+	 * function. If it has changed, it concludes that the last key was a
+	 * modifier and then deletes it from the buffer of pressed keycodes.
+	 * For us the equivalent would look something like this:
+	 *
+	 * static uint32_t last_modifiers;
+	 * bool last_key_was_a_modifier = last_modifiers != modifiers;
+	 * last_modifiers = modifiers;
+	 * if (last_key_was_a_modifier) {
+	 *	key_state_remove_last_pressed_key(last_pressed_keycode);
+	 * }
+	 */
+
+	bool ismodifier = false;
+	for (int i = 0; i < translated.nr_syms; i++) {
+		ismodifier |= is_modifier_key(translated.syms[i]);
+	}
+	if (!ismodifier) {
 		key_state_set_pressed(event->keycode,
 			event->state == WL_KEYBOARD_KEY_STATE_PRESSED);
+	}
 
 	/*
 	 * Ignore labwc keybindings if input is inhibited
@@ -293,13 +319,7 @@ handle_compositor_keybindings(struct keyboard *keyboard,
 
 			/* cycle to next */
 			bool backwards = modifiers & WLR_MODIFIER_SHIFT;
-			/* ignore if this is a modifier key being pressed */
-			bool ignore = false;
-			for (int i = 0; i < translated.nr_syms; i++) {
-				ignore |= is_modifier_key(translated.syms[i]);
-			}
-
-			if (!ignore) {
+			if (!ismodifier) {
 				enum lab_cycle_dir dir = backwards
 					? LAB_CYCLE_DIR_BACKWARD
 					: LAB_CYCLE_DIR_FORWARD;
@@ -313,6 +333,19 @@ handle_compositor_keybindings(struct keyboard *keyboard,
 		goto out;
 	}
 
+	/*
+	 * A keybind is not considered valid if other keys are pressed at the
+	 * same time.
+	 *
+	 * In labwc, a keybind is defined by one/many modifier keys + _one_
+	 * non-modifier key. Returning early on >1 pressed non-modifier keys
+	 * avoids false positive matches where 'other' keys were pressed at the
+	 * same time.
+	 */
+	if (key_state_nr_pressed_keys() > 1) {
+		return false;
+	}
+
 	/*
 	 * Handle compositor keybinds
 	 *