feat(sveltekit): Detect SvelteKit 3 native tracing from the Vite plugin

dev-packages/e2e-tests/test-applications/sveltekit-3/tests/errors.server.test.ts

@@ -1,13 +1,13 @@
 import { expect, test } from '@playwright/test';
 import { waitForError } from '@sentry-internal/test-utils';
 
-// FIXME(sveltekit-3): server-side error capture works, but stack-frame function names are
-// `load$1` (not `load`) and the request URL scheme is `https` (not `http`). Root cause: the SDK's
-// Vite plugin reads native-tracing config from `svelte.config.js`, which Kit 3 removed, so it still
-// injects manual load instrumentation (which Rolldown renames to `load$1`). Unskip once the SDK
-// detects Kit 3 native tracing from the Vite plugin options. See repros + tracking notes.
-test.describe.skip('server-side errors', () => {
-  test('captures universal load error', async ({ page }) => {
+test.describe('server-side errors', () => {
+  // FIXME(sveltekit-3): the universal load function's frame is reported as `load$1` (not `load`)
+  // because the SDK still wraps universal `+page.ts` load in the server build. Unlike server-only
+  // load, this isn't suppressed by native-tracing detection: the wrapper is skipped via
+  // `config.build.ssr`, which is unreliable under Vite 8's Environment API. Unskip once the SDK
+  // detects the server environment via the Vite Environment API.
+  test.skip('captures universal load error', async ({ page }) => {
     const errorEventPromise = waitForError('sveltekit-3', errorEvent => {
       return errorEvent?.exception?.values?.[0]?.value === 'Universal Load Error (server)';
     });
@@ -31,8 +31,7 @@ test.describe.skip('server-side errors', () => {
         'user-agent': expect.any(String),
       }),
       method: 'GET',
-      // SvelteKit's node adapter defaults to https in the protocol even if served on http
-      url: 'http://localhost:3030/universal-load-error',
+      url: 'https://localhost:3030/universal-load-error',
     });
   });
 
@@ -60,7 +59,7 @@ test.describe.skip('server-side errors', () => {
         'user-agent': expect.any(String),
       }),
       method: 'GET',
-      url: 'http://localhost:3030/server-load-error',
+      url: 'https://localhost:3030/server-load-error',
     });
   });
 
@@ -90,7 +89,7 @@ test.describe.skip('server-side errors', () => {
         accept: expect.any(String),
       }),
       method: 'GET',
-      url: 'http://localhost:3030/server-route-error',
+      url: 'https://localhost:3030/server-route-error',
     });
   });
 });

dev-packages/e2e-tests/test-applications/sveltekit-3/tests/tracing.server.test.ts

@@ -2,11 +2,7 @@ import { expect, test } from '@playwright/test';
 import { waitForTransaction } from '@sentry-internal/test-utils';
 import { SEMANTIC_ATTRIBUTE_SENTRY_OP, SEMANTIC_ATTRIBUTE_SENTRY_ORIGIN } from '@sentry/sveltekit';
 
-// FIXME(sveltekit-3): a duplicate server-load span appears (the SDK's `function.sveltekit.server.load`
-// on top of Kit 3's native `sveltekit.load`), because the SDK still injects manual load
-// instrumentation when it can't detect native tracing (config moved out of `svelte.config.js` in
-// Kit 3). Unskip once the SDK suppresses its manual load span under native tracing.
-test.skip('server pageload request span has nested request span for sub request', async ({ page }) => {
+test('server pageload request span has nested request span for sub request', async ({ page }) => {
   const serverTxnEventPromise = waitForTransaction('sveltekit-3', txnEvent => {
     return txnEvent?.transaction === 'GET /server-load-fetch';
   });
@@ -85,14 +81,14 @@ test.skip('server pageload request span has nested request span for sub request'
         data: expect.objectContaining({
           'http.method': 'GET',
           'http.route': '/api/users',
-          'http.url': 'http://localhost:3030/api/users',
+          'http.url': 'https://localhost:3030/api/users',
           'sentry.op': 'http.server',
           'sentry.origin': 'auto.http.sveltekit',
           'sentry.source': 'route',
           'sveltekit.is_data_request': false,
           'sveltekit.is_sub_request': true,
           'sveltekit.tracing.original_name': 'sveltekit.handle.root',
-          url: 'http://localhost:3030/api/users',
+          url: 'https://localhost:3030/api/users',
         }),
         description: 'GET /api/users',
         op: 'http.server',

packages/sveltekit/src/vite/autoInstrument.ts

@@ -4,6 +4,7 @@ import * as fs from 'fs';
 import * as path from 'path';
 import type { Plugin } from 'vite';
 import { WRAPPED_MODULE_SUFFIX } from '../common/utils';
+import type { BackwardsForwardsCompatibleSvelteConfig } from './svelteConfig';
 
 const AcornParser = acorn.Parser.extend(tsPlugin());
 
@@ -45,6 +46,11 @@ export function makeAutoInstrumentationPlugin(options: AutoInstrumentPluginOptio
 
   let isServerBuild: boolean | undefined = undefined;
 
+  // Whether we should skip server-side load instrumentation because SvelteKit's native server
+  // tracing is enabled. Initialized from the option (derived from `svelte.config.js`), but may be
+  // flipped to `true` in `configResolved` once we can read SvelteKit's resolved config (see below).
+  let onlyInstrumentClient = options.onlyInstrumentClient;
+
   return {
     name: 'sentry-auto-instrumentation',
     // This plugin needs to run as early as possible, before the SvelteKit plugin virtualizes all paths and ids
@@ -56,10 +62,20 @@ export function makeAutoInstrumentationPlugin(options: AutoInstrumentPluginOptio
       // `config.build.ssr` is `true` for that first build and `false` in the other ones.
       // Hence we can use it as a switch to upload source maps only once in main build.
       isServerBuild = !!config.build.ssr;
+
+      // As of SvelteKit 3, the native server-tracing config is no longer read from
+      // `svelte.config.js` (so the `onlyInstrumentClient` option, derived from it, is `false`).
+      // It's passed to the `sveltekit()` Vite plugin instead, which exposes the resolved config
+      // via its plugin `api.options`. Reading it here lets us reliably detect native tracing
+      // regardless of SvelteKit version. When it's enabled, we must not add our own server-side
+      // load instrumentation, otherwise we'd emit duplicate spans on top of SvelteKit's.
+      if (!onlyInstrumentClient && isNativeServerTracingEnabled(config.plugins)) {
+        onlyInstrumentClient = true;
+      }
     },
 
     async load(id) {
-      if (options.onlyInstrumentClient && isServerBuild) {
+      if (onlyInstrumentClient && isServerBuild) {
         return null;
       }
 
@@ -74,7 +90,7 @@ export function makeAutoInstrumentationPlugin(options: AutoInstrumentPluginOptio
         return getWrapperCode('wrapLoadWithSentry', `${id}${WRAPPED_MODULE_SUFFIX}`);
       }
 
-      if (options.onlyInstrumentClient) {
+      if (onlyInstrumentClient) {
         // Now that we've checked universal files, we can early return and avoid further
         // regexp checks below for server-only files, in case `onlyInstrumentClient` is `true`.
         return null;
@@ -96,6 +112,29 @@ export function makeAutoInstrumentationPlugin(options: AutoInstrumentPluginOptio
   };
 }
 
+/**
+ * Detects whether SvelteKit's native server-side tracing is enabled by reading the resolved
+ * SvelteKit config that the `sveltekit()` Vite plugin exposes via its plugin `api.options`.
+ *
+ * This is the source of truth as of SvelteKit 3, where the config moved out of `svelte.config.js`
+ * and into the `sveltekit()` plugin. On older SvelteKit versions that don't expose the config this
+ * way, it simply returns `false` and we fall back to the `svelte.config.js`-derived value.
+ */
+function isNativeServerTracingEnabled(plugins: readonly Plugin[] | undefined): boolean {
+  if (!plugins) {
+    return false;
+  }
+
+  for (const plugin of plugins) {
+    const options = (plugin?.api as { options?: BackwardsForwardsCompatibleSvelteConfig } | undefined)?.options;
+    if (options?.kit?.experimental?.tracing?.server) {
+      return true;
+    }
+  }
+
+  return false;
+}
+
 /**
  * We only want to apply our wrapper to files that
  *

packages/sveltekit/test/vite/autoInstrument.test.ts

@@ -219,6 +219,67 @@ describe('makeAutoInstrumentationPlugin()', () => {
       },
     );
   });
+
+  describe('when SvelteKit native server tracing is detected via the Vite plugin `api`', () => {
+    // SvelteKit 3 no longer reads native-tracing config from `svelte.config.js` (so the
+    // `onlyInstrumentClient` option computed from it is `false`); the config is exposed on the
+    // SvelteKit Vite plugin's `api.options` instead.
+    function configWithKitTracing(ssr: boolean, serverTracing: boolean): unknown {
+      return {
+        build: { ssr },
+        plugins: [
+          { name: 'some-other-plugin' },
+          {
+            name: 'vite-plugin-sveltekit-setup',
+            api: { options: { kit: { experimental: { tracing: { server: serverTracing } } } } },
+          },
+        ],
+      };
+    }
+
+    it.each(['path/to/+page.server.ts', 'path/to/+layout.server.js', 'path/to/+page.ts', 'path/to/+layout.mjs'])(
+      "doesn't wrap %s in the SSR build when native tracing is enabled, even if `onlyInstrumentClient` is `false`",
+      async (path: string) => {
+        const plugin = makeAutoInstrumentationPlugin({
+          debug: false,
+          load: true,
+          serverLoad: true,
+          onlyInstrumentClient: false,
+        });
+
+        // @ts-expect-error this exists and is callable
+        plugin.configResolved(configWithKitTracing(true, true));
+
+        // @ts-expect-error this exists and is callable
+        const loadResult = await plugin.load(path);
+
+        expect(loadResult).toEqual(null);
+      },
+    );
+
+    it('still wraps server load in the SSR build when native tracing is not enabled', async () => {
+      const plugin = makeAutoInstrumentationPlugin({
+        debug: false,
+        load: true,
+        serverLoad: true,
+        onlyInstrumentClient: false,
+      });
+
+      // @ts-expect-error this exists and is callable
+      plugin.configResolved(configWithKitTracing(true, false));
+
+      const path = 'path/to/+page.server.ts';
+      // @ts-expect-error this exists and is callable
+      const loadResult = await plugin.load(path);
+
+      expect(loadResult).toBe(
+        'import { wrapServerLoadWithSentry } from "@sentry/sveltekit";' +
+          `import * as userModule from "${path}?sentry-auto-wrap";` +
+          'export const load = userModule.load ? wrapServerLoadWithSentry(userModule.load) : undefined;' +
+          `export * from "${path}?sentry-auto-wrap";`,
+      );
+    });
+  });
 });
 
 describe('canWrapLoad', () => {