fix: allow mocking CJS module with interoped default

examples/mocks/src/external/default-function.cjs

@@ -0,0 +1,3 @@
+module.exports = function () {
+  return true
+}

examples/mocks/test/external.test.ts

@@ -1,7 +1,14 @@
 import '../src/external/external.mjs'
 import { expect, test, vi } from 'vitest'
 import axios from 'axios'
+import defaultFunc from '../src/external/default-function.cjs'
+
+vi.mock('../src/external/default-function.cjs')
 
 test('axios is mocked', () => {
   expect(vi.isMockFunction(axios.get)).toBe(true)
 })
+
+test('defaultFunc is mocked', () => {
+  expect(vi.isMockFunction(defaultFunc)).toBe(true)
+})

examples/mocks/vite.config.ts

@@ -25,6 +25,7 @@ export default defineConfig({
     environment: 'node',
     deps: {
       external: [/src\/external/],
+      interopDefault: true,
     },
   },
 })

packages/vite-node/src/client.ts

@@ -424,6 +424,14 @@ export class ViteNodeRunner {
 
     const { mod, defaultExport } = interopModule(importedModule)
 
+    const modKeys = Reflect.ownKeys(mod)
+    let defaultKeys = !isPrimitive(defaultExport) ? Reflect.ownKeys(defaultExport) : []
+    // remove reserved keys from default keys
+    if (typeof mod !== 'function' && typeof defaultExport === 'function') {
+      const reservedKeys = ['arguments', 'caller', 'prototype', 'name', 'length']
+      defaultKeys = defaultKeys.filter(n => typeof n === 'string' && !reservedKeys.includes(n))
+    }
+
     return new Proxy(mod, {
       get(mod, prop) {
         if (prop === 'default')
@@ -436,11 +444,10 @@ export class ViteNodeRunner {
         return prop in mod || (defaultExport && prop in defaultExport)
       },
       // this is needed for mocker to know what is available to mock
-      ownKeys(mod) {
-        const keys = Reflect.ownKeys(mod)
+      ownKeys() {
         if (!defaultExport || isPrimitive(defaultExport))
-          return keys
-        const allKeys = [...keys, 'default', ...Reflect.ownKeys(defaultExport)]
+          return modKeys
+        const allKeys = [...modKeys, 'default', ...defaultKeys]
         return Array.from(new Set(allKeys))
       },
       getOwnPropertyDescriptor(mod, prop) {

packages/vitest/src/runtime/execute.ts

@@ -73,6 +73,8 @@ export class VitestRunner extends ViteNodeRunner {
   }
 
   shouldInterop(path: string, mod: any) {
-    return this.options.interopDefault ?? (getCurrentEnvironment() !== 'node' && super.shouldInterop(path, mod))
+    if (this.options.interopDefault === false)
+      return false
+    return (this.options.interopDefault || getCurrentEnvironment() !== 'node') && super.shouldInterop(path, mod)
   }
 }