perf(legacy): skip lowering when detecting polyfills (vitejs#20387)

Author: sapphi-red

packages/plugin-legacy/package.json

@@ -35,6 +35,8 @@
   "dependencies": {
     "@babel/core": "^7.28.0",
     "@babel/preset-env": "^7.28.0",
+    "babel-plugin-polyfill-corejs3": "^0.13.0",
+    "babel-plugin-polyfill-regenerator": "^0.6.5",
     "browserslist": "^4.25.1",
     "browserslist-to-esbuild": "^2.1.1",
     "core-js": "^3.44.0",

packages/plugin-legacy/src/index.ts

@@ -554,7 +554,9 @@ function viteLegacyPlugin(options: Options = {}): Plugin[] {
         compact: !!config.build.minify,
         sourceMaps,
         inputSourceMap: undefined,
+        targets,
         assumptions,
+        browserslistConfigFile: false,
         presets: [
           // forcing our plugin to run before preset-env by wrapping it in a
           // preset so we can catch the injected import statements...
@@ -569,7 +571,18 @@ function viteLegacyPlugin(options: Options = {}): Plugin[] {
           ],
           [
             (await import('@babel/preset-env')).default,
-            createBabelPresetEnvOptions(targets, { needPolyfills }),
+            {
+              bugfixes: true,
+              modules: false,
+              useBuiltIns: needPolyfills ? 'usage' : false,
+              corejs: needPolyfills
+                ? {
+                    version: _require('core-js/package.json').version,
+                    proposals: false,
+                  }
+                : undefined,
+              shippedProposals: true,
+            },
           ],
         ],
       })
@@ -741,14 +754,27 @@ export async function detectPolyfills(
   const babel = await loadBabel()
   const result = babel.transform(code, {
     ast: true,
+    code: false,
     babelrc: false,
     configFile: false,
     compact: false,
+    targets,
     assumptions,
-    presets: [
+    browserslistConfigFile: false,
+    plugins: [
       [
-        (await import('@babel/preset-env')).default,
-        createBabelPresetEnvOptions(targets, {}),
+        (await import('babel-plugin-polyfill-corejs3')).default,
+        {
+          method: 'usage-global',
+          version: _require('core-js/package.json').version,
+          shippedProposals: true,
+        },
+      ],
+      [
+        (await import('babel-plugin-polyfill-regenerator')).default,
+        {
+          method: 'usage-global',
+        },
       ],
     ],
   })
@@ -765,27 +791,6 @@ export async function detectPolyfills(
   }
 }
 
-function createBabelPresetEnvOptions(
-  targets: any,
-  { needPolyfills = true }: { needPolyfills?: boolean },
-) {
-  return {
-    targets,
-    bugfixes: true,
-    loose: false,
-    modules: false,
-    useBuiltIns: needPolyfills ? 'usage' : false,
-    corejs: needPolyfills
-      ? {
-          version: _require('core-js/package.json').version,
-          proposals: false,
-        }
-      : undefined,
-    shippedProposals: true,
-    ignoreBrowserslistConfig: true,
-  }
-}
-
 async function buildPolyfillChunk(
   mode: string,
   imports: Set<string>,

packages/plugin-legacy/src/shims.d.ts

@@ -0,0 +1,3 @@
+declare module 'babel-plugin-polyfill-corejs3'
+
+declare module 'babel-plugin-polyfill-regenerator'