seat: Refocus seat when wlr_drag is destroyed

wlr_drag installs grabs for the full duration of the drag, leading to
the drag target not being focused when the drag ends. This leads to
unexpected focus behavior, especially for the keyboard which requires
toggling focus away and back to set.

We can only fix the focus once the grabs are released, so refocus the
seat when the wlr_drag destroy event is received.

Closes: https://github.com/swaywm/sway/issues/5116

include/sway/input/seat.h

@@ -64,6 +64,12 @@ struct sway_drag_icon {
 	struct wl_listener destroy;
 };
 
+struct sway_drag {
+	struct sway_seat *seat;
+	struct wlr_drag *wlr_drag;
+	struct wl_listener destroy;
+};
+
 struct sway_seat {
 	struct wlr_seat *wlr_seat;
 	struct sway_cursor *cursor;

sway/input/seat.c

@@ -402,6 +402,31 @@ static void drag_icon_handle_destroy(struct wl_listener *listener, void *data) {
 	free(icon);
 }
 
+static void drag_handle_destroy(struct wl_listener *listener, void *data) {
+	struct sway_drag *drag = wl_container_of(listener, drag, destroy);
+
+	// Focus enter isn't sent during drag, so refocus the focused node, layer
+	// surface or unmanaged surface.
+	struct sway_seat *seat = drag->seat;
+	struct sway_node *focus = seat_get_focus(seat);
+	if (focus) {
+		seat_set_focus(seat, NULL);
+		seat_set_focus(seat, focus);
+	} else if (seat->focused_layer) {
+		struct wlr_layer_surface_v1 *layer = seat->focused_layer;
+		seat_set_focus_layer(seat, NULL);
+		seat_set_focus_layer(seat, layer);
+	} else {
+		struct wlr_surface *unmanaged = seat->wlr_seat->keyboard_state.focused_surface;
+		seat_set_focus_surface(seat, NULL, false);
+		seat_set_focus_surface(seat, unmanaged, false);
+	}
+
+	drag->wlr_drag->data = NULL;
+	wl_list_remove(&drag->destroy.link);
+	free(drag);
+}
+
 static void handle_request_start_drag(struct wl_listener *listener,
 		void *data) {
 	struct sway_seat *seat = wl_container_of(listener, seat, request_start_drag);
@@ -431,6 +456,19 @@ static void handle_request_start_drag(struct wl_listener *listener,
 static void handle_start_drag(struct wl_listener *listener, void *data) {
 	struct sway_seat *seat = wl_container_of(listener, seat, start_drag);
 	struct wlr_drag *wlr_drag = data;
+
+	struct sway_drag *drag = calloc(1, sizeof(struct sway_drag));
+	if (drag == NULL) {
+		sway_log(SWAY_ERROR, "Allocation failed");
+		return;
+	}
+	drag->seat = seat;
+	drag->wlr_drag = wlr_drag;
+	wlr_drag->data = drag;
+
+	drag->destroy.notify = drag_handle_destroy;
+	wl_signal_add(&wlr_drag->events.destroy, &drag->destroy);
+
 	struct wlr_drag_icon *wlr_drag_icon = wlr_drag->icon;
 	if (wlr_drag_icon == NULL) {
 		return;