fix(sveltekit): Only instrument SvelteKit fetch if the SDK client is valid (#8381)

In the client-side SvelteKit fetch instrumentation, our previous type
cast when retrieving the SDK client was wrong, causing us to not guard
the fetch instrumentation correctly if the client was undefined. This fix
adds an undefined check.

fixes #8290

Author: Lms24

packages/sveltekit/src/client/load.ts

@@ -3,7 +3,7 @@ import type { BaseClient } from '@sentry/core';
 import { getCurrentHub, trace } from '@sentry/core';
 import type { Breadcrumbs, BrowserTracing } from '@sentry/svelte';
 import { captureException } from '@sentry/svelte';
-import type { ClientOptions, SanitizedRequestData } from '@sentry/types';
+import type { Client, ClientOptions, SanitizedRequestData } from '@sentry/types';
 import {
   addExceptionMechanism,
   addNonEnumerableProperty,
@@ -122,12 +122,14 @@ type SvelteKitFetch = LoadEvent['fetch'];
  * @returns a proxy of SvelteKit's fetch implementation
  */
 function instrumentSvelteKitFetch(originalFetch: SvelteKitFetch): SvelteKitFetch {
-  const client = getCurrentHub().getClient() as BaseClient<ClientOptions>;
+  const client = getCurrentHub().getClient();
 
-  const browserTracingIntegration =
-    client.getIntegrationById && (client.getIntegrationById('BrowserTracing') as BrowserTracing | undefined);
-  const breadcrumbsIntegration =
-    client.getIntegrationById && (client.getIntegrationById('Breadcrumbs') as Breadcrumbs | undefined);
+  if (!isValidClient(client)) {
+    return originalFetch;
+  }
+
+  const browserTracingIntegration = client.getIntegrationById('BrowserTracing') as BrowserTracing | undefined;
+  const breadcrumbsIntegration = client.getIntegrationById('Breadcrumbs') as Breadcrumbs | undefined;
 
   const browserTracingOptions = browserTracingIntegration && browserTracingIntegration.options;
 
@@ -270,3 +272,14 @@ function addFetchBreadcrumb(
     },
   );
 }
+
+type MaybeClientWithGetIntegrationsById =
+  | (Client & { getIntegrationById?: BaseClient<ClientOptions>['getIntegrationById'] })
+  | undefined;
+
+type ClientWithGetIntegrationById = Required<MaybeClientWithGetIntegrationsById> &
+  Exclude<MaybeClientWithGetIntegrationsById, undefined>;
+
+function isValidClient(client: MaybeClientWithGetIntegrationsById): client is ClientWithGetIntegrationById {
+  return !!client && typeof client.getIntegrationById === 'function';
+}

packages/sveltekit/test/client/load.test.ts

@@ -52,6 +52,12 @@ const mockedGetIntegrationById = vi.fn(id => {
   return undefined;
 });
 
+const mockedGetClient = vi.fn(() => {
+  return {
+    getIntegrationById: mockedGetIntegrationById,
+  };
+});
+
 vi.mock('@sentry/core', async () => {
   const original = (await vi.importActual('@sentry/core')) as any;
   return {
@@ -62,11 +68,7 @@ vi.mock('@sentry/core', async () => {
     },
     getCurrentHub: () => {
       return {
-        getClient: () => {
-          return {
-            getIntegrationById: mockedGetIntegrationById,
-          };
-        },
+        getClient: mockedGetClient,
         getScope: () => {
           return {
             getSpan: () => {
@@ -427,6 +429,28 @@ describe('wrapLoadWithSentry', () => {
     });
   });
 
+  it.each([
+    ['is undefined', undefined],
+    ["doesn't have a `getClientById` method", {}],
+  ])("doesn't instrument fetch if the client %s", async (_, client) => {
+    // @ts-expect-error: we're mocking the client
+    mockedGetClient.mockImplementationOnce(() => client);
+
+    async function load(_event: Parameters<Load>[0]): Promise<ReturnType<Load>> {
+      return {
+        msg: 'hi',
+      };
+    }
+    const wrappedLoad = wrapLoadWithSentry(load);
+
+    const originalFetch = MOCK_LOAD_ARGS.fetch;
+    await wrappedLoad(MOCK_LOAD_ARGS);
+
+    expect(MOCK_LOAD_ARGS.fetch).toStrictEqual(originalFetch);
+
+    expect(mockTrace).toHaveBeenCalledTimes(1);
+  });
+
   it('adds an exception mechanism', async () => {
     const addEventProcessorSpy = vi.spyOn(mockScope, 'addEventProcessor').mockImplementationOnce(callback => {
       void callback({}, { event_id: 'fake-event-id' });