feat(legacy): add rolldown-vite support (#20417)

Author: sapphi-red

packages/plugin-legacy/package.json

@@ -32,8 +32,16 @@
   },
   "homepage": "https://github.com/vitejs/vite/tree/main/packages/plugin-legacy#readme",
   "funding": "https://github.com/vitejs/vite?sponsor=1",
+  "imports": {
+    "#legacy-for-rolldown-vite": {
+      "types": "./types/legacy-for-rolldown-vite.d.ts",
+      "default": "./dist/vendor/rolldown-vite/index.js"
+    }
+  },
   "dependencies": {
     "@babel/core": "^7.28.0",
+    "@babel/plugin-transform-dynamic-import": "^7.27.1",
+    "@babel/plugin-transform-modules-systemjs": "^7.27.1",
     "@babel/preset-env": "^7.28.0",
     "babel-plugin-polyfill-corejs3": "^0.13.0",
     "babel-plugin-polyfill-regenerator": "^0.6.5",
@@ -49,7 +57,9 @@
     "vite": "^7.0.0"
   },
   "devDependencies": {
+    "@vitejs/plugin-legacy-for-rolldown-vite": "https://pkg.pr.new/vitejs/rolldown-vite/@vitejs/plugin-legacy@b19b90a",
     "acorn": "^8.15.0",
+    "fdir": "^6.4.6",
     "picocolors": "^1.1.1",
     "tsdown": "^0.12.9",
     "vite": "workspace:*"

packages/plugin-legacy/src/index.ts

@@ -3,6 +3,7 @@ import crypto from 'node:crypto'
 import { createRequire } from 'node:module'
 import { fileURLToPath } from 'node:url'
 import { build, normalizePath } from 'vite'
+import * as vite from 'vite'
 import MagicString from 'magic-string'
 import type {
   BuildOptions,
@@ -125,6 +126,13 @@ const nonLeadingHashInFileNameRE = /[^/]+\[hash(?::\d+)?\]/
 const prefixedHashInFileNameRE = /\W?\[hash(?::\d+)?\]/
 
 function viteLegacyPlugin(options: Options = {}): Plugin[] {
+  if ('rolldownVersion' in vite) {
+    const { default: viteLegacyPluginForRolldownVite } = _require(
+      '#legacy-for-rolldown-vite',
+    )
+    return viteLegacyPluginForRolldownVite(options)
+  }
+
   let config: ResolvedConfig
   let targets: Options['targets']
   let modernTargets: Options['modernTargets']

packages/plugin-legacy/tsdown.config.ts

@@ -1,8 +1,66 @@
+import path from 'node:path'
+import fs from 'node:fs'
 import { defineConfig } from 'tsdown'
+import { fdir } from 'fdir'
+
+const pluginLegacyForRolldownVitePackagePath = path.resolve(
+  import.meta.dirname,
+  './node_modules/@vitejs/plugin-legacy-for-rolldown-vite',
+)
 
 export default defineConfig({
   entry: ['src/index.ts'],
   target: 'node20',
   tsconfig: false, // disable tsconfig `paths` when bundling
   dts: true,
+  hooks: {
+    async 'build:done'() {
+      validateAllDepsForRolldownViteIsIncluded()
+
+      const files = new fdir()
+        .glob('!**/*.d.ts')
+        .withRelativePaths()
+        .crawl(path.join(pluginLegacyForRolldownVitePackagePath, 'dist'))
+        .sync()
+      for (const file of files) {
+        const src = path.resolve(
+          pluginLegacyForRolldownVitePackagePath,
+          'dist',
+          file,
+        )
+        const dist = path.resolve(
+          import.meta.dirname,
+          'dist/vendor/rolldown-vite',
+          file,
+        )
+        fs.mkdirSync(path.dirname(dist), { recursive: true })
+        fs.copyFileSync(src, dist)
+      }
+    },
+  },
 })
+
+function validateAllDepsForRolldownViteIsIncluded() {
+  const pkgJsonStr = fs.readFileSync(
+    path.resolve(import.meta.dirname, 'package.json'),
+    'utf-8',
+  )
+  const pkgJson = JSON.parse(pkgJsonStr)
+
+  const pkgJsonForRolldownViteStr = fs.readFileSync(
+    path.resolve(pluginLegacyForRolldownVitePackagePath, 'package.json'),
+    'utf-8',
+  )
+  const pkgJsonForRolldownVite = JSON.parse(pkgJsonForRolldownViteStr)
+
+  for (const depName of Object.keys(
+    pkgJsonForRolldownVite.dependencies ?? {},
+  )) {
+    if (!pkgJson.dependencies[depName]) {
+      throw new Error(
+        `All deps for rolldown-vite version of @vitejs/plugin-legacy should be ` +
+          `included in @vitejs/plugin-legacy, but ${depName} is not included.`,
+      )
+    }
+  }
+}

packages/plugin-legacy/types/legacy-for-rolldown-vite.d.ts

@@ -0,0 +1,5 @@
+import type { Plugin } from 'vite'
+import type { Options } from '../src/types'
+
+declare const plugin: (options?: Options) => Plugin[]
+export default plugin