Bypass webpack compilation for precompiled @next/polyfills-nomodule (#27596)

Removes the extra webpack handling that was previously done, this ensures the file which is already minified and compiled does not get passed through minification again.

Largely based on #21418
Closes #21418

The polyfill loading already has tests so no other changes are necessary.



## Bug

- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Errors have helpful link attached, see `contributing.md`

## Feature

- [ ] Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.
- [ ] Errors have helpful link attached, see `contributing.md`

## Documentation / Examples

- [ ] Make sure the linting passes

packages/next/build/webpack-config.ts

@@ -19,7 +19,7 @@ import { getTypeScriptConfiguration } from '../lib/typescript/getTypeScriptConfi
 import {
   CLIENT_STATIC_FILES_RUNTIME_AMP,
   CLIENT_STATIC_FILES_RUNTIME_MAIN,
-  CLIENT_STATIC_FILES_RUNTIME_POLYFILLS,
+  CLIENT_STATIC_FILES_RUNTIME_POLYFILLS_SYMBOL,
   CLIENT_STATIC_FILES_RUNTIME_REACT_REFRESH,
   CLIENT_STATIC_FILES_RUNTIME_WEBPACK,
   REACT_LOADABLE_MANIFEST,
@@ -52,6 +52,7 @@ import WebpackConformancePlugin, {
 } from './webpack/plugins/webpack-conformance-plugin'
 import { WellKnownErrorsPlugin } from './webpack/plugins/wellknown-errors-plugin'
 import { regexLikeCss } from './webpack/config/blocks/css'
+import { CopyFilePlugin } from './webpack/plugins/copy-file-plugin'
 
 type ExcludesFalse = <T>(x: T | false) => x is T
 
@@ -378,10 +379,6 @@ export default async function getBaseWebpackConfig(
               )
             )
             .replace(/\\/g, '/'),
-        [CLIENT_STATIC_FILES_RUNTIME_POLYFILLS]: path.join(
-          NEXT_PROJECT_ROOT_DIST_CLIENT,
-          'polyfills.js'
-        ),
       } as ClientEntries)
     : undefined
 
@@ -1343,6 +1340,18 @@ export default async function getBaseWebpackConfig(
           ].filter(Boolean),
         }),
       new WellKnownErrorsPlugin(),
+      !isServer &&
+        new CopyFilePlugin({
+          filePath: require.resolve('./polyfills/polyfill-nomodule'),
+          cacheKey: process.env.__NEXT_VERSION as string,
+          name: `static/chunks/polyfills${dev ? '' : '-[hash]'}.js`,
+          minimize: false,
+          info: {
+            [CLIENT_STATIC_FILES_RUNTIME_POLYFILLS_SYMBOL]: 1,
+            // This file is already minified
+            minimized: true,
+          },
+        }),
     ].filter((Boolean as any) as ExcludesFalse),
   }
 

packages/next/build/webpack/plugins/build-manifest-plugin.ts

@@ -8,7 +8,7 @@ import {
   BUILD_MANIFEST,
   CLIENT_STATIC_FILES_PATH,
   CLIENT_STATIC_FILES_RUNTIME_MAIN,
-  CLIENT_STATIC_FILES_RUNTIME_POLYFILLS,
+  CLIENT_STATIC_FILES_RUNTIME_POLYFILLS_SYMBOL,
   CLIENT_STATIC_FILES_RUNTIME_REACT_REFRESH,
   CLIENT_STATIC_FILES_RUNTIME_AMP,
 } from '../../../shared/lib/constants'
@@ -146,9 +146,24 @@ export default class BuildManifestPlugin {
         getEntrypointFiles(entrypoints.get(CLIENT_STATIC_FILES_RUNTIME_MAIN))
       )
 
-      assetMap.polyfillFiles = getEntrypointFiles(
-        entrypoints.get(CLIENT_STATIC_FILES_RUNTIME_POLYFILLS)
-      ).filter((file) => !mainFiles.has(file))
+      const compilationAssets: {
+        name: string
+        source: typeof sources.RawSource
+        info: object
+      }[] = compilation.getAssets()
+
+      assetMap.polyfillFiles = compilationAssets
+        .filter((p) => {
+          // Ensure only .js files are passed through
+          if (!p.name.endsWith('.js')) {
+            return false
+          }
+
+          return (
+            p.info && CLIENT_STATIC_FILES_RUNTIME_POLYFILLS_SYMBOL in p.info
+          )
+        })
+        .map((v) => v.name)
 
       assetMap.devFiles = getEntrypointFiles(
         entrypoints.get(CLIENT_STATIC_FILES_RUNTIME_REACT_REFRESH)
@@ -160,7 +175,6 @@ export default class BuildManifestPlugin {
 
       const systemEntrypoints = new Set([
         CLIENT_STATIC_FILES_RUNTIME_MAIN,
-        CLIENT_STATIC_FILES_RUNTIME_POLYFILLS,
         CLIENT_STATIC_FILES_RUNTIME_REACT_REFRESH,
         CLIENT_STATIC_FILES_RUNTIME_AMP,
       ])

packages/next/build/webpack/plugins/copy-file-plugin.ts

@@ -0,0 +1,89 @@
+import { promises as fs } from 'fs'
+import loaderUtils from 'next/dist/compiled/loader-utils'
+import {
+  isWebpack5,
+  sources,
+  webpack,
+} from 'next/dist/compiled/webpack/webpack'
+
+const PLUGIN_NAME = 'CopyFilePlugin'
+
+export class CopyFilePlugin {
+  private filePath: string
+  private name: string
+  private cacheKey: string
+  private info?: object
+
+  constructor({
+    filePath,
+    cacheKey,
+    name,
+    info,
+  }: {
+    filePath: string
+    cacheKey: string
+    name: string
+    minimize: boolean
+    info?: object
+  }) {
+    this.filePath = filePath
+    this.cacheKey = cacheKey
+    this.name = name
+    this.info = info
+  }
+
+  apply(compiler: webpack.Compiler) {
+    compiler.hooks.thisCompilation.tap(PLUGIN_NAME, (compilation: any) => {
+      const cache = isWebpack5 ? compilation.getCache('CopyFilePlugin') : null
+      const hook = isWebpack5
+        ? // @ts-ignore
+          compilation.hooks.processAssets
+        : compilation.hooks.additionalAssets
+      hook.tapPromise(
+        isWebpack5
+          ? {
+              name: PLUGIN_NAME,
+              // @ts-ignore TODO: Remove ignore when webpack 5 is stable
+              stage: webpack.Compilation.PROCESS_ASSETS_STAGE_ADDITIONS,
+            }
+          : PLUGIN_NAME,
+        async () => {
+          if (cache) {
+            const cachedResult = await cache.getPromise(
+              this.filePath,
+              this.cacheKey
+            )
+            if (cachedResult) {
+              const { file, source } = cachedResult
+              compilation.emitAsset(file, source, {
+                ...this.info,
+              })
+              return
+            }
+          }
+          const content = await fs.readFile(this.filePath, 'utf8')
+
+          const file = loaderUtils.interpolateName(
+            { resourcePath: this.filePath },
+            this.name,
+            { content, context: compiler.context }
+          )
+
+          const source = new sources.RawSource(content)
+
+          if (cache) {
+            await cache.storePromise(this.filePath, this.cacheKey, {
+              file,
+              source,
+            })
+          }
+
+          // @ts-ignore
+          compilation.emitAsset(file, source, {
+            ...this.info,
+          })
+        }
+      )
+    })
+  }
+}

packages/next/client/polyfills.js

@@ -1 +0,0 @@
-import 'next/dist/build/polyfills/polyfill-nomodule'

packages/next/shared/lib/constants.ts

@@ -32,7 +32,7 @@ export const CLIENT_STATIC_FILES_RUNTIME_AMP = `amp`
 // static/runtime/webpack.js
 export const CLIENT_STATIC_FILES_RUNTIME_WEBPACK = `webpack`
 // static/runtime/polyfills.js
-export const CLIENT_STATIC_FILES_RUNTIME_POLYFILLS = `polyfills`
+export const CLIENT_STATIC_FILES_RUNTIME_POLYFILLS_SYMBOL = Symbol(`polyfills`)
 export const TEMPORARY_REDIRECT_STATUS = 307
 export const PERMANENT_REDIRECT_STATUS = 308
 export const STATIC_PROPS_ID = '__N_SSG'