fix(sveltekit): Avoid data invalidation in wrapped client-side load functions (#9071)

This patch fixes a data invalidation issue that appeared on the client side
when auto-instrumenting or manually wrapping universal `load` functions.
Because our `wrapLoadWithSentry` function accessed `event.route.id`, the
data returned from `load` would be invalidated on a route change. As
reported in #8818 , this caused prefetched, actually still valid data to be
invalidated during the navigation to the page, causing another `load`
invocation.

To avoid this invalidation, we change the way how we read the route.id,
to first use `Object.getOwnPropertyDescriptor` which doesn't trigger the
proxy that listens to accesses. This, however, will only work for
`@sveltejs/kit>=1.24.0` which includes a
[change](sveltejs/kit#10576) to the Kit-internal
proxy. For older versions of kit, we continue to directly read from
`event.route.id`, which will still cause invalidations. Not ideal but
IMO the best we can do without loosing data.

closes #8818

Author: Lms24

packages/sveltekit/src/client/load.ts

@@ -71,7 +71,17 @@ export function wrapLoadWithSentry<T extends (...args: any) => any>(origLoad: T)
 
       addNonEnumerableProperty(patchedEvent as unknown as Record<string, unknown>, '__sentry_wrapped__', true);
 
-      const routeId = event.route.id;
+      // Accessing any member of `event.route` causes SvelteKit to invalidate the
+      // client-side universal `load` function's data prefetched data, causing another reload on the actual navigation.
+      // To work around this, we use `Object.getOwnPropertyDescriptor` which doesn't invoke the proxy.
+      const routeIdDescriptor = event.route && Object.getOwnPropertyDescriptor(event.route, 'id');
+      // First, we try to access the route id from the property descriptor.
+      // This will only work for @sveltejs/kit >= 1.24.0
+      const routeIdFromDescriptor = routeIdDescriptor && (routeIdDescriptor.value as string | undefined);
+      // If routeIdFromDescriptor is undefined, we fall back to the old behavior of accessing
+      // `event.route.id` directly. This will still cause invalidations but we get a route name.
+      const routeId = routeIdFromDescriptor || event.route.id;
+
       return trace(
         {
           op: 'function.sveltekit.load',