data-device: unbreak wl_data_source.cancel during drag-and-drop

include/wlr/types/wlr_data_device.h

@@ -127,7 +127,7 @@ struct wlr_drag {
 	struct wlr_surface *focus; // can be NULL
 	struct wlr_data_source *source; // can be NULL
 
-	bool started, cancelling;
+	bool started, dropped, cancelling;
 	int32_t grab_touch_id, touch_id; // if WLR_DRAG_GRAB_TOUCH
 
 	struct {

types/data_device/wlr_data_offer.c

@@ -111,20 +111,6 @@ static void data_offer_dnd_finish(struct wlr_data_offer *offer) {
 
 static void data_offer_handle_destroy(struct wl_client *client,
 		struct wl_resource *resource) {
-	struct wlr_data_offer *offer = data_offer_from_resource(resource);
-	if (offer == NULL) {
-		goto out;
-	}
-
-	// If the drag destination has version < 3, wl_data_offer.finish
-	// won't be called, so do this here as a safety net, because
-	// we still want the version >= 3 drag source to be happy.
-	if (wl_resource_get_version(offer->resource) <
-			WL_DATA_OFFER_ACTION_SINCE_VERSION) {
-		data_offer_dnd_finish(offer);
-	}
-
-out:
 	wl_resource_destroy(resource);
 }
 
@@ -204,6 +190,18 @@ void data_offer_destroy(struct wlr_data_offer *offer) {
 	wl_list_remove(&offer->source_destroy.link);
 	wl_list_remove(&offer->link);
 
+	if (offer->type == WLR_DATA_OFFER_DRAG) {
+		// If the drag destination has version < 3, wl_data_offer.finish
+		// won't be called, so do this here as a safety net, because
+		// we still want the version >= 3 drag source to be happy.
+		if (wl_resource_get_version(offer->resource) <
+				WL_DATA_OFFER_ACTION_SINCE_VERSION) {
+			data_offer_dnd_finish(offer);
+		} else if (offer->source && offer->source->impl->dnd_finish) {
+			wlr_data_source_destroy(offer->source);
+		}
+	}
+
 	// Make the resource inert
 	wl_resource_set_user_data(offer->resource, NULL);
 
@@ -227,6 +225,8 @@ static void data_offer_handle_source_destroy(struct wl_listener *listener,
 		void *data) {
 	struct wlr_data_offer *offer =
 		wl_container_of(listener, offer, source_destroy);
+	// Prevent data_offer_destroy from destroying the source again
+	offer->source = NULL;
 	data_offer_destroy(offer);
 }
 

types/data_device/wlr_drag.c

@@ -28,6 +28,20 @@ static void drag_set_focus(struct wlr_drag *drag,
 	if (drag->focus_client) {
 		wl_list_remove(&drag->seat_client_destroy.link);
 
+		// If we're switching focus to another client, we want to destroy all
+		// offers without destroying the source. If the drag operation ends, we
+		// want to keep the offer around for the data transfer.
+		struct wlr_data_offer *offer, *tmp;
+		wl_list_for_each_safe(offer, tmp,
+				&drag->focus_client->seat->drag_offers, link) {
+			struct wl_client *client = wl_resource_get_client(offer->resource);
+			if (!drag->dropped && offer->source == drag->source &&
+					client == drag->focus_client->client) {
+				offer->source = NULL;
+				data_offer_destroy(offer);
+			}
+		}
+
 		struct wl_resource *resource;
 		wl_resource_for_each(resource, &drag->focus_client->data_devices) {
 			wl_data_device_send_leave(resource);
@@ -37,20 +51,20 @@ static void drag_set_focus(struct wlr_drag *drag,
 		drag->focus = NULL;
 	}
 
-	if (!surface || !surface->resource) {
-		return;
+	if (!surface) {
+		goto out;
 	}
 
 	if (!drag->source &&
 			wl_resource_get_client(surface->resource) !=
 			drag->seat_client->client) {
-		return;
+		goto out;
 	}
 
 	struct wlr_seat_client *focus_client = wlr_seat_client_for_wl_client(
 		drag->seat_client->seat, wl_resource_get_client(surface->resource));
 	if (!focus_client) {
-		return;
+		goto out;
 	}
 
 	if (drag->source != NULL) {
@@ -88,6 +102,7 @@ static void drag_set_focus(struct wlr_drag *drag,
 	drag->seat_client_destroy.notify = drag_handle_seat_client_destroy;
 	wl_signal_add(&focus_client->events.destroy, &drag->seat_client_destroy);
 
+out:
 	wlr_signal_emit_safe(&drag->events.focus, drag);
 }
 
@@ -164,26 +179,36 @@ static void drag_handle_pointer_motion(struct wlr_seat_pointer_grab *grab,
 	}
 }
 
-static uint32_t drag_handle_pointer_button(struct wlr_seat_pointer_grab *grab,
-		uint32_t time, uint32_t button, uint32_t state) {
-	struct wlr_drag *drag = grab->data;
+static void drag_drop(struct wlr_drag *drag, uint32_t time) {
+	assert(drag->focus_client);
+
+	drag->dropped = true;
 
-	if (drag->source &&
-			grab->seat->pointer_state.grab_button == button &&
-			state == WL_POINTER_BUTTON_STATE_RELEASED) {
-		if (drag->focus_client && drag->source->current_dnd_action &&
-				drag->source->accepted) {
 	struct wl_resource *resource;
 	wl_resource_for_each(resource, &drag->focus_client->data_devices) {
 		wl_data_device_send_drop(resource);
 	}
+	if (drag->source) {
 		wlr_data_source_dnd_drop(drag->source);
+	}
 
 	struct wlr_drag_drop_event event = {
 		.drag = drag,
 		.time = time,
 	};
 	wlr_signal_emit_safe(&drag->events.drop, &event);
+}
+
+static uint32_t drag_handle_pointer_button(struct wlr_seat_pointer_grab *grab,
+		uint32_t time, uint32_t button, uint32_t state) {
+	struct wlr_drag *drag = grab->data;
+
+	if (drag->source &&
+			grab->seat->pointer_state.grab_button == button &&
+			state == WL_POINTER_BUTTON_STATE_RELEASED) {
+		if (drag->focus_client && drag->source->current_dnd_action &&
+				drag->source->accepted) {
+			drag_drop(drag, time);
 		} else if (drag->source->impl->dnd_finish) {
 			// This will end the grab and free `drag`
 			wlr_data_source_destroy(drag->source);
@@ -233,10 +258,7 @@ static void drag_handle_touch_up(struct wlr_seat_touch_grab *grab,
 	}
 
 	if (drag->focus_client) {
-		struct wl_resource *resource;
-		wl_resource_for_each(resource, &drag->focus_client->data_devices) {
-			wl_data_device_send_drop(resource);
-		}
+		drag_drop(drag, time);
 	}
 
 	drag_destroy(drag);