touchpad: special-case shift as modifier for dwt

We ignore modifiers for disable-while-typing because we don't want to
disable the touchpad for things like shift-click or ctrl-click.

We also do remember the modifier state so that we don't disable the
touchpad for once-offs like ctrl+s.

Shift is however a special case - shift + something else is means the
user is typing and we should disable the touchpad for that.

Closes #1005

Part-of: <https://gitlab.freedesktop.org/libinput/libinput/-/merge_requests/1015>

src/evdev-mt-touchpad.c

@@ -2248,6 +2248,12 @@ tp_keyboard_timeout(uint64_t now, void *data)
 	evdev_log_debug(tp->device, "palm: keyboard timeout\n");
 }
 
+static inline bool
+tp_key_is_shift(unsigned int keycode)
+{
+	return keycode == KEY_LEFTSHIFT || keycode == KEY_RIGHTSHIFT;
+}
+
 static inline bool
 tp_key_is_modifier(unsigned int keycode)
 {
@@ -2320,10 +2326,14 @@ tp_keyboard_event(uint64_t time, struct libinput_event *event, void *data)
 		return;
 
 	/* modifier keys don't trigger disable-while-typing so things like
-	 * ctrl+zoom or ctrl+click are possible */
+	 * ctrl+zoom or ctrl+click are possible.
+	 * The exception is shift which we don't trigger DWT for on its own
+	 * but we do trigger DWT for once we type some other key.
+	 */
 	is_modifier = tp_key_is_modifier(key);
 	if (is_modifier) {
-		long_set_bit(tp->dwt.mod_mask, key);
+		if (!tp_key_is_shift(key))
+			long_set_bit(tp->dwt.mod_mask, key);
 		return;
 	}
 

test/test-touchpad.c

@@ -4259,6 +4259,50 @@ START_TEST(touchpad_dwt_modifier_no_dwt)
 }
 END_TEST
 
+START_TEST(touchpad_dwt_shift_combo_triggers_dwt)
+{
+	struct litest_device *touchpad = litest_current_device();
+	struct litest_device *keyboard;
+	struct libinput *li = touchpad->libinput;
+	unsigned int modifiers[] = {
+		KEY_LEFTSHIFT,
+		KEY_RIGHTSHIFT,
+	};
+
+	if (!has_disable_while_typing(touchpad))
+		return;
+
+	keyboard = dwt_init_paired_keyboard(li, touchpad);
+	litest_disable_tap(touchpad->libinput_device);
+	litest_disable_hold_gestures(touchpad->libinput_device);
+	litest_drain_events(li);
+
+	ARRAY_FOR_EACH(modifiers, key) {
+		litest_keyboard_key(keyboard, *key, true);
+		litest_keyboard_key(keyboard, KEY_A, true);
+		litest_keyboard_key(keyboard, KEY_A, false);
+		litest_keyboard_key(keyboard, *key, false);
+		libinput_dispatch(li);
+
+		litest_assert_only_typed_events(li, LIBINPUT_EVENT_KEYBOARD_KEY);
+
+		litest_touch_down(touchpad, 0, 50, 50);
+		litest_touch_move_to(touchpad, 0, 50, 50, 70, 50, 5);
+		litest_touch_up(touchpad, 0);
+		litest_assert_empty_queue(li);
+	}
+
+	litest_timeout_dwt_long();
+	libinput_dispatch(li);
+	litest_touch_down(touchpad, 0, 50, 50);
+	litest_touch_move_to(touchpad, 0, 50, 50, 70, 50, 5);
+	litest_touch_up(touchpad, 0);
+	litest_assert_only_typed_events(li, LIBINPUT_EVENT_POINTER_MOTION);
+
+	litest_delete_device(keyboard);
+}
+END_TEST
+
 START_TEST(touchpad_dwt_modifier_combo_no_dwt)
 {
 	struct litest_device *touchpad = litest_current_device();
@@ -4269,8 +4313,6 @@ START_TEST(touchpad_dwt_modifier_combo_no_dwt)
 		KEY_RIGHTCTRL,
 		KEY_LEFTALT,
 		KEY_RIGHTALT,
-		KEY_LEFTSHIFT,
-		KEY_RIGHTSHIFT,
 		KEY_FN,
 		KEY_CAPSLOCK,
 		KEY_TAB,
@@ -4318,8 +4360,6 @@ START_TEST(touchpad_dwt_modifier_combo_dwt_after)
 		KEY_RIGHTCTRL,
 		KEY_LEFTALT,
 		KEY_RIGHTALT,
-		KEY_LEFTSHIFT,
-		KEY_RIGHTSHIFT,
 		KEY_FN,
 		KEY_CAPSLOCK,
 		KEY_TAB,
@@ -4371,8 +4411,6 @@ START_TEST(touchpad_dwt_modifier_combo_dwt_remains)
 		KEY_RIGHTCTRL,
 		KEY_LEFTALT,
 		KEY_RIGHTALT,
-		KEY_LEFTSHIFT,
-		KEY_RIGHTSHIFT,
 		KEY_FN,
 		KEY_CAPSLOCK,
 		KEY_TAB,
@@ -7372,6 +7410,7 @@ TEST_COLLECTION(touchpad)
 	litest_add(touchpad_dwt_key_hold_timeout_existing_touch_cornercase, LITEST_TOUCHPAD, LITEST_ANY);
 	litest_add(touchpad_dwt_type, LITEST_TOUCHPAD, LITEST_ANY);
 	litest_add(touchpad_dwt_type_short_timeout, LITEST_TOUCHPAD, LITEST_ANY);
+	litest_add(touchpad_dwt_shift_combo_triggers_dwt, LITEST_TOUCHPAD, LITEST_ANY);
 	litest_add(touchpad_dwt_modifier_no_dwt, LITEST_TOUCHPAD, LITEST_ANY);
 	litest_add(touchpad_dwt_modifier_combo_no_dwt, LITEST_TOUCHPAD, LITEST_ANY);
 	litest_add(touchpad_dwt_modifier_combo_dwt_after, LITEST_TOUCHPAD, LITEST_ANY);