feat: show error when accessing variables not exposed in CJS build

packages/vite/index.cjs

@@ -1,3 +1,6 @@
+const description =
+  ' See https://vite.dev/guide/troubleshooting.html#vite-cjs-node-api-deprecated for more details.'
+
 warnCjsUsage()
 
 // type utils
@@ -17,12 +20,43 @@ const asyncFunctions = [
   'formatPostcssSourceMap',
   'loadConfigFromFile',
   'preprocessCSS',
+  'createBuilder',
 ]
 asyncFunctions.forEach((name) => {
   module.exports[name] = (...args) =>
     import('./dist/node/index.js').then((i) => i[name](...args))
 })
 
+// variables and sync functions that cannot be used from cjs build
+const disallowedVariables = [
+  // was not exposed in cjs from the beginning
+  'parseAst',
+  'parseAstAsync',
+  'buildErrorMessage',
+  'sortUserPlugins',
+  // Environment API related variables that are too big to include in the cjs build
+  'DevEnvironment',
+  'BuildEnvironment',
+  'createIdResolver',
+  'createRunnableDevEnvironment',
+  // can be redirected from ESM, but doesn't make sense as it's Environment API related
+  'fetchModule',
+  'moduleRunnerTransform',
+  // can be exposed, but doesn't make sense as it's Environment API related
+  'createServerHotChannel',
+  'createServerModuleRunner',
+  'isRunnableDevEnvironment',
+]
+disallowedVariables.forEach((name) => {
+  Object.defineProperty(module.exports, name, {
+    get() {
+      throw new Error(
+        `${name} is not available in the CJS build of Vite.` + description,
+      )
+    },
+  })
+})
+
 function warnCjsUsage() {
   if (process.env.VITE_CJS_IGNORE_WARNING) return
   const logLevelIndex = process.argv.findIndex((arg) =>
@@ -39,9 +73,7 @@ function warnCjsUsage() {
   }
   const yellow = (str) => `\u001b[33m${str}\u001b[39m`
   console.warn(
-    yellow(
-      `The CJS build of Vite's Node API is deprecated. See https://vite.dev/guide/troubleshooting.html#vite-cjs-node-api-deprecated for more details.`,
-    ),
+    yellow("The CJS build of Vite's Node API is deprecated." + description),
   )
   if (process.env.VITE_CJS_TRACE) {
     const e = {}

packages/vite/rollup.config.ts

@@ -201,7 +201,11 @@ const cjsConfig = defineConfig({
     format: 'cjs',
   },
   external: Object.keys(pkg.dependencies),
-  plugins: [...createSharedNodePlugins({}), bundleSizeLimit(175)],
+  plugins: [
+    ...createSharedNodePlugins({}),
+    bundleSizeLimit(175),
+    exportCheck(),
+  ],
 })
 
 export default defineConfig([
@@ -342,4 +346,29 @@ function bundleSizeLimit(limit: number): Plugin {
   }
 }
 
+function exportCheck(): Plugin {
+  return {
+    name: 'export-check',
+    async writeBundle() {
+      // escape import so that it's not bundled while config load
+      const dynImport = (id: string) => import(id)
+
+      const esmNamespace = await dynImport('./dist/node/index.js')
+      const cjsModuleExports = (await dynImport('./index.cjs')).default
+      const cjsModuleExportsKeys = new Set(
+        Object.getOwnPropertyNames(cjsModuleExports),
+      )
+      const lackingExports = Object.keys(esmNamespace).filter(
+        (key) => !cjsModuleExportsKeys.has(key),
+      )
+      if (lackingExports.length > 0) {
+        this.error(
+          `Exports missing from cjs build: ${lackingExports.join(', ')}.` +
+            ` Please update index.cjs or src/publicUtils.ts.`,
+        )
+      }
+    },
+  }
+}
+
 // #endregion