fix(ssr): use browser platform for webworker SSR builds (fix #21969)

packages/vite/src/node/build.ts

@@ -24,6 +24,7 @@ import type {
   WatcherOptions,
 } from 'rolldown'
 import { viteLoadFallbackPlugin as nativeLoadFallbackPlugin } from 'rolldown/experimental'
+import { esmExternalRequirePlugin } from 'rolldown/plugins'
 import type { EsbuildTarget } from '#types/internal/esbuildOptions'
 import type { RollupCommonJSOptions } from '#dep-types/commonjs'
 import type { RollupDynamicImportVarsOptions } from '#dep-types/dynamicImportVars'
@@ -420,6 +421,7 @@ export function resolveBuildEnvironmentOptions(
   logger: Logger,
   consumer: 'client' | 'server' | undefined,
   isBundledDev: boolean,
+  isSsrTargetWebworkerEnvironment?: boolean,
 ): ResolvedBuildEnvironmentOptions {
   const deprecatedPolyfillModulePreload = raw.polyfillModulePreload
   const { polyfillModulePreload, ...rest } = raw
@@ -451,7 +453,10 @@ export function resolveBuildEnvironmentOptions(
   )
   setupRollupOptionCompat(merged, 'build')
   merged.rolldownOptions = {
-    platform: consumer === 'server' ? 'node' : 'browser',
+    platform:
+      consumer === 'client' || isSsrTargetWebworkerEnvironment
+        ? 'browser'
+        : 'node',
     ...merged.rolldownOptions,
   }
 
@@ -654,6 +659,12 @@ export function resolveRolldownOptions(
     environment.name === 'ssr' &&
     environment.getTopLevelConfig().ssr?.target === 'webworker'
 
+  // For webworker SSR with platform: 'browser', external CJS require() calls
+  // need to be converted to ESM imports since createRequire is not available.
+  if (isSsrTargetWebworkerEnvironment) {
+    plugins.push(esmExternalRequirePlugin())
+  }
+
   const buildOutputOptions = (output: OutputOptions = {}): OutputOptions => {
     // @ts-expect-error See https://github.com/vitejs/vite/issues/5812#issuecomment-984345618
     if (output.output) {

packages/vite/src/node/config.ts

@@ -969,6 +969,7 @@ function resolveEnvironmentOptions(
       logger,
       consumer,
       isBundledDev,
+      isSsrTargetWebworkerEnvironment,
     ),
     plugins: undefined!, // to be resolved later
     // will be set by `setOptimizeDepsPluginNames` later

playground/ssr-webworker/__tests__/ssr-webworker.spec.ts

@@ -30,6 +30,12 @@ test('supports nodejs_compat', async () => {
   )
 })
 
+test.runIf(isBuild)('build output does not contain createRequire', async () => {
+  const workerContent = findAssetFile(/entry-worker/, 'worker', '')
+  expect(workerContent).toBeDefined()
+  expect(workerContent).not.toContain('createRequire')
+})
+
 test.runIf(isBuild)('codeSplitting: false', () => {
   const dynamicJsContent = findAssetFile(/dynamic-[-\w]+\.js/, 'worker')
   expect(dynamicJsContent).toBeUndefined()