fix(sveltekit): Stop adapter-node 6 output dir probe from deleting the build

To learn the Node adapter's output directory we call its adapt() with a stub
builder. adapter-node 6 deletes its output dir with fs.rmSync before it uses
the builder, so loading the Vite config (vite dev, svelte-kit sync, ...)
wiped the user's build/ folder. Run adapt() from an empty temp cwd so the
relative delete hits the temp dir instead.

The stub builder also only had the SvelteKit 2 config shape (config.kit.paths),
so adapter-node 6 threw before reporting a custom out dir and we fell back to
build. Provide the SvelteKit 3 shape (config.paths) as well.

Fixes #25186
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: chargome

packages/sveltekit/src/vite/sentryVitePlugins.ts

@@ -38,9 +38,9 @@ export async function sentrySvelteKit(options: SentrySvelteKitPluginOptions = {}
   const getAdapter = (): Promise<SupportedSvelteKitAdapters> =>
     (adapterPromise ??= (async () => options.adapter || detectAdapter(await getKitConfig(), options.debug))());
 
-  // Side effect: for the Node adapter we invoke `adapter.adapt()` to learn the output directory,
-  // and `@sveltejs/adapter-node` v6 wipes that directory when it runs. So this must happen once,
-  // before the build writes anything - never from a late hook like `closeBundle`.
+  // For the Node adapter we invoke `adapter.adapt()` to learn the output directory. It runs from a temp
+  // cwd so it can't wipe the real output, but it's still resolved once and before the build writes
+  // anything, never from a late hook like `closeBundle`, in case an adapter deletes an absolute `out`.
   let adapterOutputDirPromise: Promise<string> | undefined;
   const getAdapterOutputDirOnce = (): Promise<string> =>
     (adapterOutputDirPromise ??= (async () => getAdapterOutputDir(await getKitConfig(), await getAdapter()))());

packages/sveltekit/src/vite/svelteConfig.ts

@@ -1,5 +1,6 @@
 import type { Builder } from '@sveltejs/kit';
 import * as fs from 'fs';
+import * as os from 'os';
 import * as path from 'path';
 import * as url from 'url';
 import type { SupportedSvelteKitAdapters } from './detectAdapter';
@@ -106,7 +107,11 @@ async function getNodeAdapterOutputDir(kitConfig: ResolvedKitConfig): Promise<st
     rimraf: () => {},
     mkdirp: () => {},
 
+    // SvelteKit 3 passes the kit config directly (`config.paths`), SvelteKit 2 nests it (`config.kit.paths`)
     config: {
+      paths: {
+        base: kitConfig.paths?.base || '',
+      },
       kit: {
         // @ts-expect-error - the builder expects a validated config but for our purpose it's fine to just pass this partial config
         paths: {
@@ -116,10 +121,33 @@ async function getNodeAdapterOutputDir(kitConfig: ResolvedKitConfig): Promise<st
     },
   };
 
+  // `@sveltejs/adapter-node` v6 deletes its (relative) output dir with `fs.rmSync` before it touches the
+  // builder, so our no-op `rimraf` doesn't help. Running `adapt()` from an empty temp cwd keeps it from
+  // wiping the user's real build output. The rm and `writeClient` both run synchronously, so the cwd is
+  // only changed for the synchronous part of the call and no other code observes it.
+  const originalCwd = process.cwd();
+  let sandboxDir: string | undefined;
+  let adaptResult: unknown;
   try {
-    await nodeAdapter.adapt(adapterBuilder);
+    sandboxDir = fs.mkdtempSync(path.join(os.tmpdir(), 'sentry-sveltekit-'));
+    process.chdir(sandboxDir);
+    adaptResult = nodeAdapter.adapt(adapterBuilder);
   } catch {
     // We expect the adapter to throw in writeClient!
+  } finally {
+    if (process.cwd() !== originalCwd) {
+      process.chdir(originalCwd);
+    }
+  }
+
+  try {
+    await adaptResult;
+  } catch {
+    // We expect the adapter to throw in writeClient!
+  }
+
+  if (sandboxDir) {
+    fs.rmSync(sandboxDir, { recursive: true, force: true });
   }
 
   return outputDir;

packages/sveltekit/test/vite/svelteConfig.test.ts

@@ -1,12 +1,17 @@
+import type * as FsModule from 'fs';
+import * as os from 'os';
+import * as path from 'path';
 import { beforeEach, describe, expect, it, vi } from 'vitest';
 import type { SupportedSvelteKitAdapters } from '../../src/vite/detectAdapter';
 import { getAdapterOutputDir, getHooksFileName, loadSvelteConfig } from '../../src/vite/svelteConfig';
 
 let existsFile: any;
 
 describe('loadSvelteConfig', () => {
-  vi.mock('fs', () => {
+  vi.mock('fs', async importOriginal => {
+    const actual = await importOriginal<typeof FsModule>();
     return {
+      ...actual,
       existsSync: () => existsFile,
     };
   });
@@ -67,6 +72,35 @@ describe('getAdapterOutputDir', () => {
     expect(outputDir).toEqual('customBuildDir');
   });
 
+  it("doesn't let the Node adapter delete the real output directory", async () => {
+    const actualFs = await vi.importActual<typeof FsModule>('fs');
+    const originalCwd = process.cwd();
+    const projectDir = actualFs.mkdtempSync(path.join(os.tmpdir(), 'sentry-sveltekit-test-'));
+    actualFs.mkdirSync(path.join(projectDir, 'customOut'));
+    actualFs.writeFileSync(path.join(projectDir, 'customOut', 'index.js'), '');
+
+    // Like `@sveltejs/adapter-node` v6, which removes its output dir itself instead of via `builder.rimraf`
+    const nodeAdapter = {
+      name: '@sveltejs/adapter-node',
+      async adapt(builder: any) {
+        actualFs.rmSync('customOut', { force: true, recursive: true });
+        builder.writeClient(`customOut/client${builder.config.paths.base}`);
+      },
+    };
+
+    process.chdir(projectDir);
+    try {
+      const outputDir = await getAdapterOutputDir({ adapter: nodeAdapter }, 'node');
+
+      expect(outputDir).toEqual('customOut');
+      expect(process.cwd()).toEqual(actualFs.realpathSync(projectDir));
+      expect(actualFs.readdirSync(path.join(projectDir, 'customOut'))).toEqual(['index.js']);
+    } finally {
+      process.chdir(originalCwd);
+      actualFs.rmSync(projectDir, { force: true, recursive: true });
+    }
+  });
+
   it('returns the output directory of the Cloudflare adapter', async () => {
     const outputDir = await getAdapterOutputDir({ outDir: 'customOutDir' }, 'cloudflare');
     expect(outputDir).toEqual('customOutDir/cloudflare');