drm-lease-v1: fix error codepath

We were crashing in the error codepath [1] when
wlr_drm_create_lease() fails.

To fix this, delay the creation of the wlr_drm_lease_v1 until the
request is granted. Previously we were allocating that struct early
without populating the drm_lease field. However that means we ended
up with a half-constructed struct in the error codepath which is
annoying to handle.

[1]: https://github.com/swaywm/sway/issues/7204#issuecomment-1269797356

include/wlr/types/wlr_drm_lease_v1.h

@@ -71,8 +71,7 @@ struct wlr_drm_lease_request_v1 {
 	struct wlr_drm_lease_connector_v1 **connectors;
 	size_t n_connectors;
 
-	/** NULL until the lease is submitted */
+	struct wl_resource *lease_resource;
-	struct wlr_drm_lease_v1 *lease;
 
 	bool invalid;
 

types/wlr_drm_lease_v1.c

@@ -154,12 +154,17 @@ static void lease_handle_destroy(struct wl_listener *listener, void *data) {
 
 struct wlr_drm_lease_v1 *wlr_drm_lease_request_v1_grant(
 		struct wlr_drm_lease_request_v1 *request) {
-	assert(request->lease);
+	assert(!request->invalid);
-
 	wlr_log(WLR_DEBUG, "Attempting to grant request %p", request);
 
-	struct wlr_drm_lease_v1 *lease = request->lease;
+	struct wlr_drm_lease_v1 *lease = calloc(1, sizeof(*lease));
-	assert(!request->invalid);
+	if (!lease) {
+		wl_resource_post_no_memory(request->resource);
+		return NULL;
+	}
+
+	lease->device = request->device;
+	lease->resource = request->lease_resource;
 
 	/* Transform connectors list into wlr_output for leasing */
 	struct wlr_output *outputs[request->n_connectors + 1];
@@ -192,6 +197,9 @@ struct wlr_drm_lease_v1 *wlr_drm_lease_request_v1_grant(
 	lease->destroy.notify = lease_handle_destroy;
 	wl_signal_add(&lease->drm_lease->events.destroy, &lease->destroy);
 
+	wl_list_insert(&lease->device->leases, &lease->link);
+	wl_resource_set_user_data(lease->resource, lease);
+
 	wlr_log(WLR_DEBUG, "Granting request %p", request);
 
 	wp_drm_lease_v1_send_lease_fd(lease->resource, fd);
@@ -202,12 +210,12 @@ struct wlr_drm_lease_v1 *wlr_drm_lease_request_v1_grant(
 
 void wlr_drm_lease_request_v1_reject(
 		struct wlr_drm_lease_request_v1 *request) {
-	assert(request && request->lease);
+	assert(request);
 
 	wlr_log(WLR_DEBUG, "Rejecting request %p", request);
 
 	request->invalid = true;
-	wp_drm_lease_v1_send_finished(request->lease->resource);
+	wp_drm_lease_v1_send_finished(request->lease_resource);
 }
 
 void wlr_drm_lease_v1_revoke(struct wlr_drm_lease_v1 *lease) {
@@ -337,20 +345,7 @@ static void drm_lease_request_v1_handle_submit(
 		}
 	}
 
-	struct wlr_drm_lease_v1 *lease = calloc(1, sizeof(struct wlr_drm_lease_v1));
+	request->lease_resource = lease_resource;
-	if (!lease) {
-		wlr_log(WLR_ERROR, "Failed to allocate wlr_drm_lease_v1");
-		wl_resource_post_no_memory(resource);
-		return;
-	}
-
-	lease->device = request->device;
-	wl_list_insert(&lease->device->leases, &lease->link);
-
-	lease->resource = lease_resource;
-	wl_resource_set_user_data(lease_resource, lease);
-
-	request->lease = lease;
 
 	/* TODO: reject the request if the user does not grant it */
 	wl_signal_emit_mutable(&request->device->manager->events.request,