fix(optimizer): preserve excluded optional peer require fallbacks

packages/vite/src/node/optimizer/index.ts

@@ -833,7 +833,7 @@ async function prepareRolldownOptimizerRun(
 
   const plugins = await asyncFlatten(arraify(pluginsFromConfig))
   if (external.length) {
-    plugins.push(rolldownCjsExternalPlugin(external, platform))
+    plugins.push(rolldownCjsExternalPlugin(external, platform, environment))
   }
   plugins.push(...rolldownDepPlugin(environment, flatIdDeps, external))
 

packages/vite/src/node/optimizer/rolldownDepPlugin.ts

@@ -376,6 +376,7 @@ const matchesEntireLine = (text: string) => `^${escapeRegex(text)}$`
 export function rolldownCjsExternalPlugin(
   externals: string[],
   platform: 'node' | 'browser' | 'neutral',
+  environment: Environment,
 ): Plugin | undefined {
   // Skip this plugin for `platform: 'node'` as `require` is available in Node
   // and that is more accurate than converting to `import`
@@ -393,18 +394,36 @@ export function rolldownCjsExternalPlugin(
 
   const filter = new RegExp(externals.map(matchesEntireLine).join('|'))
 
+  const packageCache: PackageCache = new Map()
+  const resolveRequire = createBackCompatIdResolver(
+    environment.getTopLevelConfig(),
+    { asSrc: false, isRequire: true, scan: true, packageCache },
+  )
+
   return {
     name: 'cjs-external',
     resolveId: {
       filter: { id: [prefixRegex(nonFacadePrefix), filter] },
-      handler(id, _importer, options) {
+      async handler(id, importer, options) {
         if (id.startsWith(nonFacadePrefix)) {
           return {
             id: id.slice(nonFacadePrefix.length),
             external: 'absolute',
           }
         }
         if (options.kind === 'require-call') {
+          // A missing optional peer must throw when require() runs, not when
+          // an eager ESM facade is evaluated. Reuse the pre-bundler's CJS stub
+          // so the dependency's try/catch can still select its fallback.
+          // Other excluded deps may intentionally be unresolvable until served.
+          const resolved = await resolveRequire(
+            environment,
+            id,
+            importer,
+          ).catch(() => undefined)
+          if (resolved?.startsWith(optionalPeerDepId)) {
+            return { id: optionalPeerDepNamespace + resolved }
+          }
           return {
             id: cjsExternalFacadeNamespace + id,
           }

playground/optimize-deps/__tests__/optimize-deps.spec.ts

@@ -179,6 +179,20 @@ test('dep with optional peer dep (cjs)', async () => {
     .toMatch(`[success]`)
 })
 
+test.runIf(isServe)(
+  'optimized CJS dep preserves fallback for excluded optional peer',
+  async () => {
+    const metadata = readDepOptimizationMetadata()
+    expect(Object.keys(metadata.optimized)).toContain(
+      '@vitejs/test-dep-with-excluded-optional-peer-dep-cjs',
+    )
+
+    await expect
+      .poll(() => page.textContent('.dep-with-excluded-optional-peer-dep-cjs'))
+      .toMatch(`[success]`)
+  },
+)
+
 test('dep with css import', async () => {
   await expect.poll(() => getColor('.dep-linked-include')).toBe('red')
 })

playground/optimize-deps/dep-with-excluded-optional-peer-dep-cjs/index.js

@@ -0,0 +1,9 @@
+exports.callPeerDep = function () {
+  try {
+    // This should not be hoisted as static import
+    // eslint-disable-next-line n/no-missing-require
+    return require('@vitejs/test-excluded-optional-peer')
+  } catch {
+    return 'fallback'
+  }
+}

playground/optimize-deps/dep-with-excluded-optional-peer-dep-cjs/package.json

@@ -0,0 +1,14 @@
+{
+  "name": "@vitejs/test-dep-with-excluded-optional-peer-dep-cjs",
+  "private": true,
+  "version": "0.0.0",
+  "main": "index.js",
+  "peerDependencies": {
+    "@vitejs/test-excluded-optional-peer": "0.0.0"
+  },
+  "peerDependenciesMeta": {
+    "@vitejs/test-excluded-optional-peer": {
+      "optional": true
+    }
+  }
+}

playground/optimize-deps/index.html

@@ -97,6 +97,9 @@ <h2>Import from dependency with optional peer dep (cjs)</h2>
 <div class="dep-with-optional-peer-dep-cjs"></div>
 <div class="dep-with-optional-peer-dep-cjs-error"></div>
 
+<h2>Import from optimized dependency with excluded optional peer dep (cjs)</h2>
+<div class="dep-with-excluded-optional-peer-dep-cjs"></div>
+
 <h2>Externalize known non-js files in optimize included dep</h2>
 <div class="externalize-known-non-js"></div>
 
@@ -311,6 +314,15 @@ <h2>Import the CommonJS external package that omits the js suffix</h2>
   )
 </script>
 
+<script type="module">
+  import { callPeerDep } from '@vitejs/test-dep-with-excluded-optional-peer-dep-cjs'
+
+  text(
+    '.dep-with-excluded-optional-peer-dep-cjs',
+    callPeerDep() === 'fallback' ? '[success]' : `[failed]: did not fallback`,
+  )
+</script>
+
 <script type="module">
   // should error on builtin modules (named import)
   // no node: protocol intentionally

playground/optimize-deps/package.json

@@ -41,6 +41,7 @@
     "@vitejs/test-dep-with-builtin-module-cjs": "file:./dep-with-builtin-module-cjs",
     "@vitejs/test-dep-with-builtin-module-esm": "file:./dep-with-builtin-module-esm",
     "@vitejs/test-dep-with-dynamic-import": "file:./dep-with-dynamic-import",
+    "@vitejs/test-dep-with-excluded-optional-peer-dep-cjs": "file:./dep-with-excluded-optional-peer-dep-cjs",
     "@vitejs/test-dep-with-optional-peer-dep": "file:./dep-with-optional-peer-dep",
     "@vitejs/test-dep-with-optional-peer-dep-cjs": "file:./dep-with-optional-peer-dep-cjs",
     "@vitejs/test-dep-with-optional-peer-dep-submodule": "file:./dep-with-optional-peer-dep-submodule",

playground/optimize-deps/vite.config.js

@@ -32,6 +32,7 @@ export default defineConfig({
       '@vitejs/test-dep-cjs-for-injected-import',
     ],
     exclude: [
+      '@vitejs/test-excluded-optional-peer',
       '@vitejs/test-nested-exclude',
       '@vitejs/test-dep-non-optimized',
       '@vitejs/test-dep-esm-external',