fix(legacy): modern polyfill autodetection was injecting more polyfills than needed (#14428)

Author: sapphi-red

packages/plugin-legacy/src/index.ts

@@ -123,6 +123,20 @@ function viteLegacyPlugin(options: Options = {}): Plugin[] {
   let config: ResolvedConfig
   let targets: Options['targets']
 
+  // browsers supporting ESM + dynamic import + import.meta + async generator
+  const modernTargetsEsbuild = [
+    'es2020',
+    'edge79',
+    'firefox67',
+    'chrome64',
+    'safari12',
+  ]
+  // same with above but by browserslist syntax
+  // es2020 = chrome 80+, safari 13.1+, firefox 72+, edge 80+
+  // https://github.com/evanw/esbuild/issues/121#issuecomment-646956379
+  const modernTargetsBabel =
+    'edge>=80, firefox>=72, chrome>=80, safari>=13.1, chromeAndroid>=80, iOS>=13.1'
+
   const genLegacy = options.renderLegacyChunks !== false
   const genModern = options.renderModernChunks !== false
   if (!genLegacy && !genModern) {
@@ -188,14 +202,7 @@ function viteLegacyPlugin(options: Options = {}): Plugin[] {
           // Vite's default target browsers are **not** the same.
           // See https://github.com/vitejs/vite/pull/10052#issuecomment-1242076461
           overriddenBuildTarget = config.build.target !== undefined
-          // browsers supporting ESM + dynamic import + import.meta + async generator
-          config.build.target = [
-            'es2020',
-            'edge79',
-            'firefox67',
-            'chrome64',
-            'safari12',
-          ]
+          config.build.target = modernTargetsEsbuild
         }
       }
 
@@ -375,7 +382,7 @@ function viteLegacyPlugin(options: Options = {}): Plugin[] {
           genModern
         ) {
           // analyze and record modern polyfills
-          await detectPolyfills(raw, { esmodules: true }, modernPolyfills)
+          await detectPolyfills(raw, modernTargetsBabel, modernPolyfills)
         }
 
         const ms = new MagicString(raw)