fix: preserve default export from externalized packages (fixes #10258)

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

@@ -17,6 +17,9 @@ const externalWithConversionNamespace =
   'vite:dep-pre-bundle:external-conversion'
 const convertedExternalPrefix = 'vite-dep-pre-bundle-external:'
 
+const cjsExternalFacadeNamespace = 'vite:cjs-external-facade'
+const nonFacadePrefix = 'vite-cjs-external-facade:'
+
 const externalTypes = [
   'css',
   // supported pre-processor types
@@ -270,19 +273,38 @@ export function esbuildCjsExternalPlugin(externals: string[]): Plugin {
         `^${text.replace(/[-\/\\^$*+?.()|[\]{}]/g, '\\$&')}$`
       const filter = new RegExp(externals.map(escape).join('|'))
 
-      build.onResolve({ filter: /.*/, namespace: 'external' }, (args) => ({
-        path: args.path,
-        external: true
-      }))
+      build.onResolve({ filter: new RegExp(`^${nonFacadePrefix}`) }, (args) => {
+        return {
+          path: args.path.slice(nonFacadePrefix.length),
+          external: true
+        }
+      })
+
+      build.onResolve({ filter }, (args) => {
+        if (args.kind === 'require-call') {
+          return {
+            path: args.path,
+            namespace: cjsExternalFacadeNamespace
+          }
+        }
 
-      build.onResolve({ filter }, (args) => ({
-        path: args.path,
-        namespace: 'external'
-      }))
+        return {
+          path: args.path,
+          external: true
+        }
+      })
 
-      build.onLoad({ filter: /.*/, namespace: 'external' }, (args) => ({
-        contents: `export * from ${JSON.stringify(args.path)}`
-      }))
+      build.onLoad(
+        { filter: /.*/, namespace: cjsExternalFacadeNamespace },
+        (args) => ({
+          contents:
+            `import * as m from ${JSON.stringify(
+              nonFacadePrefix + args.path
+            )};` +
+            `export default m.default;` +
+            `export * from ${JSON.stringify(nonFacadePrefix + args.path)};`
+        })
+      )
     }
   }
 }

playground/external/__tests__/external.spec.ts

@@ -7,6 +7,11 @@ test('importmap', () => {
   )
 })
 
+test('should have default exports', async () => {
+  expect(await page.textContent('#imported-slash-exists')).toBe('true')
+  expect(await page.textContent('#required-slash-exists')).toBe('true')
+})
+
 describe.runIf(isBuild)('build', () => {
   test('should externalize imported packages', async () => {
     // If `vue` is successfully externalized, the page should use the version from the import map

playground/external/dep-that-imports-vue/index.js → playground/external/dep-that-imports/index.js

@@ -1,3 +1,5 @@
 import { version } from 'vue'
+import slash from 'slash'
 
 document.querySelector('#imported-vue-version').textContent = version
+document.querySelector('#imported-slash-exists').textContent = !!slash

playground/external/dep-that-imports-vue/package.json → playground/external/dep-that-imports/package.json

@@ -1,8 +1,9 @@
 {
-  "name": "@vitejs/dep-that-imports-vue",
+  "name": "@vitejs/dep-that-imports",
   "private": true,
   "version": "0.0.0",
   "dependencies": {
+    "slash": "^5.0.0",
     "vue": "^3.2.41"
   }
 }

playground/external/dep-that-requires/index.js

@@ -0,0 +1,5 @@
+const { version } = require('vue')
+const { default: slash } = require('slash')
+
+document.querySelector('#required-vue-version').textContent = version
+document.querySelector('#required-slash-exists').textContent = !!slash

playground/external/dep-that-requires-vue/package.json → playground/external/dep-that-requires/package.json

@@ -1,8 +1,9 @@
 {
-  "name": "@vitejs/dep-that-requires-vue",
+  "name": "@vitejs/dep-that-requires",
   "private": true,
   "version": "0.0.0",
   "dependencies": {
+    "slash": "^5.0.0",
     "vue": "^3.2.41"
   }
 }

playground/external/index.html

@@ -7,14 +7,17 @@
     <script type="importmap">
       {
         "imports": {
-          "vue": "https://unpkg.com/vue@3.2.0/dist/vue.runtime.esm-browser.js"
+          "vue": "https://unpkg.com/vue@3.2.0/dist/vue.runtime.esm-browser.js",
+          "slash": "https://unpkg.com/slash@5.0.0/index.js"
         }
       }
     </script>
   </head>
   <body>
     <p>Imported Vue version: <span id="imported-vue-version"></span></p>
     <p>Required Vue version: <span id="required-vue-version"></span></p>
+    <p>Imported slash exists: <span id="imported-slash-exists"></span></p>
+    <p>Required slash exists: <span id="required-slash-exists"></span></p>
     <script type="module" src="/src/main.js"></script>
   </body>
 </html>

playground/external/package.json

@@ -9,10 +9,11 @@
     "preview": "vite preview"
   },
   "dependencies": {
-    "@vitejs/dep-that-imports-vue": "file:./dep-that-imports-vue",
-    "@vitejs/dep-that-requires-vue": "file:./dep-that-requires-vue"
+    "@vitejs/dep-that-imports": "file:./dep-that-imports",
+    "@vitejs/dep-that-requires": "file:./dep-that-requires"
   },
   "devDependencies": {
+    "slash": "^5.0.0",
     "vite": "workspace:*",
     "vue": "^3.2.41"
   }

playground/external/src/main.js

@@ -1,2 +1,2 @@
-import '@vitejs/dep-that-imports-vue'
-import '@vitejs/dep-that-requires-vue'
+import '@vitejs/dep-that-imports'
+import '@vitejs/dep-that-requires'

playground/external/vite.config.js

@@ -1,13 +1,17 @@
 import { defineConfig } from 'vite'
 
 export default defineConfig({
+  optimizeDeps: {
+    include: ['dep-that-imports', 'dep-that-requires'],
+    exclude: ['vue', 'slash']
+  },
   build: {
     minify: false,
     rollupOptions: {
-      external: ['vue']
+      external: ['vue', 'slash']
     },
     commonjsOptions: {
-      esmExternals: ['vue']
+      esmExternals: ['vue', 'slash']
     }
   }
 })