feat(sveltekit): Only inject fetch proxy script for SvelteKit < 2.16.0 (#15126)

With v9 onwards, we'll only inject the fetch proxy script into SvelteKit
versions where we actually need it. This is all kit versions below
2.16.0. I'll update docs in a follow-up PR.

fixes #15007

Author: Lms24

dev-packages/e2e-tests/test-applications/sveltekit-2-twp/.gitignore renamed to dev-packages/e2e-tests/test-applications/sveltekit-2.5.0-twp/.gitignore

@@ -1,5 +1,5 @@
 {
-  "name": "sveltekit-2-svelte-5",
+  "name": "sveltekit-2.5.0-twp",
   "version": "0.0.1",
   "private": true,
   "scripts": {
@@ -22,7 +22,7 @@
     "@sentry-internal/test-utils": "link:../../../test-utils",
     "@sentry/core": "latest || *",
     "@sveltejs/adapter-auto": "^3.0.0",
-    "@sveltejs/kit": "^2.0.0",
+    "@sveltejs/kit": "2.5.0",
     "@sveltejs/vite-plugin-svelte": "^3.0.0",
     "svelte": "^5.0.0-next.115",
     "svelte-check": "^3.6.0",

dev-packages/e2e-tests/test-applications/sveltekit-2-twp/.npmrc renamed to dev-packages/e2e-tests/test-applications/sveltekit-2.5.0-twp/.npmrc

@@ -2,5 +2,5 @@ import { startEventProxyServer } from '@sentry-internal/test-utils';
 
 startEventProxyServer({
   port: 3031,
-  proxyServerName: 'sveltekit-2-twp',
+  proxyServerName: 'sveltekit-2.5.0-twp',
 });

dev-packages/e2e-tests/test-applications/sveltekit-2-twp/README.md renamed to dev-packages/e2e-tests/test-applications/sveltekit-2.5.0-twp/README.md

@@ -2,11 +2,11 @@ import { expect, test } from '@playwright/test';
 import { waitForError } from '@sentry-internal/test-utils';
 
 test('errors on frontend and backend are connected by the same trace', async ({ page }) => {
-  const clientErrorPromise = waitForError('sveltekit-2-twp', evt => {
+  const clientErrorPromise = waitForError('sveltekit-2.5.0-twp', evt => {
     return evt.exception?.values?.[0].value === 'Client Error';
   });
 
-  const serverErrorPromise = waitForError('sveltekit-2-twp', evt => {
+  const serverErrorPromise = waitForError('sveltekit-2.5.0-twp', evt => {
     return evt.exception?.values?.[0].value === 'No search query provided';
   });
 

dev-packages/e2e-tests/test-applications/sveltekit-2-twp/package.json renamed to dev-packages/e2e-tests/test-applications/sveltekit-2.5.0-twp/package.json

@@ -0,0 +1,16 @@
+import { expect, test } from '@playwright/test';
+
+test.describe('SDK-internal behavior', () => {
+  test('Injects fetch proxy script for SvelteKit<2.16.0', async ({ page }) => {
+    await page.goto('/');
+
+    const sentryCarrier = await page.evaluate('typeof window.__SENTRY__');
+    const proxyHandle = await page.evaluate('typeof window._sentryFetchProxy');
+
+    // sanity check
+    expect(sentryCarrier).toBe('object');
+
+    // fetch proxy script ran
+    expect(proxyHandle).toBe('function');
+  });
+});

dev-packages/e2e-tests/test-applications/sveltekit-2-twp/playwright.config.mjs renamed to dev-packages/e2e-tests/test-applications/sveltekit-2.5.0-twp/playwright.config.mjs

@@ -23,7 +23,7 @@
     "@sentry/core": "latest || *",
     "@sveltejs/adapter-auto": "^3.0.0",
     "@sveltejs/adapter-node": "^2.0.0",
-    "@sveltejs/kit": "^2.5.0",
+    "@sveltejs/kit": "^2.16.0",
     "@sveltejs/vite-plugin-svelte": "^3.0.0",
     "svelte": "^4.2.8",
     "svelte-check": "^3.6.0",

dev-packages/e2e-tests/test-applications/sveltekit-2-twp/src/app.d.ts renamed to dev-packages/e2e-tests/test-applications/sveltekit-2.5.0-twp/src/app.d.ts

@@ -0,0 +1,16 @@
+import { expect, test } from '@playwright/test';
+import { waitForInitialPageload } from './utils';
+
+test.describe('SDK-internal behavior', () => {
+  test("Doesn't inject fetch proxy script for SvelteKit>=2.16.0", async ({ page }) => {
+    await waitForInitialPageload(page, { route: '/' });
+    const sentryCarrier = await page.evaluate('typeof window.__SENTRY__');
+    const proxyHandle = await page.evaluate('typeof window._sentryFetchProxy');
+
+    // sanity check
+    expect(sentryCarrier).toBe('object');
+
+    // fetch proxy script didn't run
+    expect(proxyHandle).toBe('undefined');
+  });
+});

dev-packages/e2e-tests/test-applications/sveltekit-2-twp/src/app.html renamed to dev-packages/e2e-tests/test-applications/sveltekit-2.5.0-twp/src/app.html

@@ -9,9 +9,7 @@
   "engines": {
     "node": ">=18"
   },
-  "files": [
-    "/build"
-  ],
+  "files": ["/build"],
   "main": "build/cjs/index.server.js",
   "module": "build/esm/index.server.js",
   "browser": "build/esm/index.client.js",

dev-packages/e2e-tests/test-applications/sveltekit-2-twp/src/hooks.client.ts renamed to dev-packages/e2e-tests/test-applications/sveltekit-2.5.0-twp/src/hooks.client.ts

@@ -93,10 +93,10 @@ export function addSentryCodeToPage(options: { injectFetchProxyScript: boolean }
  * ```
  */
 export function sentryHandle(handlerOptions?: SentryHandleOptions): Handle {
-  const options: Required<SentryHandleOptions> = {
-    handleUnknownRoutes: false,
-    injectFetchProxyScript: true,
-    ...handlerOptions,
+  const { handleUnknownRoutes, ...rest } = handlerOptions ?? {};
+  const options = {
+    handleUnknownRoutes: handleUnknownRoutes ?? false,
+    ...rest,
   };
 
   const sentryRequestHandler: Handle = input => {
@@ -131,12 +131,24 @@ export function sentryHandle(handlerOptions?: SentryHandleOptions): Handle {
 
 async function instrumentHandle(
   { event, resolve }: Parameters<Handle>[0],
-  options: Required<SentryHandleOptions>,
+  options: SentryHandleOptions,
 ): Promise<Response> {
   if (!event.route?.id && !options.handleUnknownRoutes) {
     return resolve(event);
   }
 
+  // caching the result of the version check in `options.injectFetchProxyScript`
+  // to avoid doing the dynamic import on every request
+  if (options.injectFetchProxyScript == null) {
+    try {
+      // @ts-expect-error - the dynamic import is fine here
+      const { VERSION } = await import('@sveltejs/kit');
+      options.injectFetchProxyScript = isFetchProxyRequired(VERSION);
+    } catch {
+      options.injectFetchProxyScript = true;
+    }
+  }
+
   const routeName = `${event.request.method} ${event.route?.id || event.url.pathname}`;
 
   if (getIsolationScope() !== getDefaultIsolationScope()) {
@@ -161,7 +173,7 @@ async function instrumentHandle(
           normalizedRequest: winterCGRequestToRequestData(event.request.clone()),
         });
         const res = await resolve(event, {
-          transformPageChunk: addSentryCodeToPage({ injectFetchProxyScript: options.injectFetchProxyScript }),
+          transformPageChunk: addSentryCodeToPage({ injectFetchProxyScript: options.injectFetchProxyScript ?? true }),
         });
         if (span) {
           setHttpStatus(span, res.status);
@@ -177,3 +189,19 @@ async function instrumentHandle(
     await flushIfServerless();
   }
 }
+
+/**
+ * We only need to inject the fetch proxy script for SvelteKit versions < 2.16.0.
+ * Exported only for testing.
+ */
+export function isFetchProxyRequired(version: string): boolean {
+  try {
+    const [major, minor] = version.trim().replace(/-.*/, '').split('.').map(Number);
+    if (major != null && minor != null && (major > 2 || (major === 2 && minor >= 16))) {
+      return false;
+    }
+  } catch {
+    // ignore
+  }
+  return true;
+}

dev-packages/e2e-tests/test-applications/sveltekit-2-twp/src/hooks.server.ts renamed to dev-packages/e2e-tests/test-applications/sveltekit-2.5.0-twp/src/hooks.server.ts

@@ -14,7 +14,7 @@ import type { Handle } from '@sveltejs/kit';
 import { redirect } from '@sveltejs/kit';
 import { vi } from 'vitest';
 
-import { FETCH_PROXY_SCRIPT, addSentryCodeToPage, sentryHandle } from '../../src/server/handle';
+import { FETCH_PROXY_SCRIPT, addSentryCodeToPage, isFetchProxyRequired, sentryHandle } from '../../src/server/handle';
 import { getDefaultNodeClientOptions } from '../utils';
 
 const mockCaptureException = vi.spyOn(SentryNode, 'captureException').mockImplementation(() => 'xx');
@@ -462,3 +462,20 @@ describe('addSentryCodeToPage', () => {
     expect(transformed).not.toContain(`<script >${FETCH_PROXY_SCRIPT}</script>`);
   });
 });
+
+describe('isFetchProxyRequired', () => {
+  it.each(['2.16.0', '2.16.1', '2.17.0', '3.0.0', '3.0.0-alpha.0'])(
+    'returns false if the version is greater than or equal to 2.16.0 (%s)',
+    version => {
+      expect(isFetchProxyRequired(version)).toBe(false);
+    },
+  );
+
+  it.each(['2.15.0', '2.15.1', '1.30.0', '1.0.0'])('returns true if the version is lower than 2.16.0 (%s)', version => {
+    expect(isFetchProxyRequired(version)).toBe(true);
+  });
+
+  it.each(['invalid', 'a.b.c'])('returns true for an invalid version (%s)', version => {
+    expect(isFetchProxyRequired(version)).toBe(true);
+  });
+});