edge-ssr: bundle next/dist as ESM for better tree-shaking (vercel#40251…

…) (vercel#40980)

Re-do of vercel#40251

Edge SSR'd routes cold boot performances are proportional to the
executed code size.

In order to improve it, we are trying to optimize for the bundle size of
a packed Edge SSR route.

This PR adds ESM compilation targets for all Next.js dist packages and
use them to bundle Edge SSR'd route.

This allows us to leverage the better tree shaking/DCE for ESM modules
in webpack in order to decrease the overall bundle size.

This PR also enables minifying Edge SSR routes. Since we don't control
which minifier might be used later (if any), it's best if we provide an
already optimised bundle.

<img width="903" alt="image"

src="https://user-images.githubusercontent.com/11064311/190005211-b7cb2c58-a56a-44b0-8ee4-fd3f603e41bd.png">

This is a 10ms cold boot win per my benchmarking script, which I'll put
in a subsequent PR.

Not done yet:
- ~~swap exported requires in `next/link` (and others) etc to point them
to the esm modules version~~

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- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
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- [x] Implements an existing feature request or RFC. Make sure the
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- [ ] 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`

- [ ] Make sure the linting passes by running `pnpm lint`
- [ ] The examples guidelines are followed from [our contributing
doc](https://github.com/vercel/next.js/blob/canary/contributing.md#adding-examples)

Co-authored-by: JJ Kasper <jj@jjsweb.site>
Co-authored-by: Shu Ding <g@shud.in>

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Thanks for opening a PR! Your contribution is much appreciated.
To make sure your PR is handled as smoothly as possible we request that
you follow the checklist sections below.
Choose the right checklist for the change that you're making:
-->

## Bug

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

## Documentation / Examples

- [ ] Make sure the linting passes by running `pnpm lint`
- [ ] The "examples guidelines" are followed from [our contributing
doc](https://github.com/vercel/next.js/blob/canary/contributing/examples/adding-examples.md)

Co-authored-by: JJ Kasper <jj@jjsweb.site>
Co-authored-by: Shu Ding <g@shud.in>

packages/next/amp.js

@@ -1 +1,4 @@
-module.exports = require('./dist/shared/lib/amp')
+module.exports =
+  process.env.NEXT_RUNTIME === 'edge'
+    ? require('./dist/esm/shared/lib/amp')
+    : require('./dist/shared/lib/amp')

packages/next/app.js

@@ -1 +1,4 @@
-module.exports = require('./dist/pages/_app')
+module.exports =
+  process.env.NEXT_RUNTIME === 'edge'
+    ? require('./dist/esm/pages/_app')
+    : require('./dist/pages/_app')

packages/next/build/entries.ts

@@ -219,6 +219,7 @@ export function getAppEntry(opts: {
   appDir: string
   appPaths: string[] | null
   pageExtensions: string[]
+  nextRuntime: string
 }) {
   return {
     import: `next-app-loader?${stringify(opts)}!`,
@@ -455,6 +456,7 @@ export async function createEntrypoints(params: CreateEntrypointsParams) {
               appDir,
               appPaths: matchedAppPaths,
               pageExtensions,
+              nextRuntime: 'nodejs',
             })
           } else if (isTargetLikeServerless(target)) {
             if (page !== '/_app' && page !== '/_document') {
@@ -479,6 +481,7 @@ export async function createEntrypoints(params: CreateEntrypointsParams) {
               appDir: appDir!,
               appPaths: matchedAppPaths,
               pageExtensions,
+              nextRuntime: 'edge',
             }).import
           }
 

packages/next/build/webpack-config.ts

@@ -180,11 +180,9 @@ export function getDefineEnv({
         }),
     // TODO: enforce `NODE_ENV` on `process.env`, and add a test:
     'process.env.NODE_ENV': JSON.stringify(dev ? 'development' : 'production'),
-    ...((isNodeServer || isEdgeServer) && {
-      'process.env.NEXT_RUNTIME': JSON.stringify(
-        isEdgeServer ? 'edge' : 'nodejs'
-      ),
-    }),
+    'process.env.NEXT_RUNTIME': JSON.stringify(
+      isEdgeServer ? 'edge' : isNodeServer ? 'nodejs' : undefined
+    ),
     'process.env.__NEXT_MIDDLEWARE_MATCHERS': JSON.stringify(
       middlewareMatchers || []
     ),
@@ -795,7 +793,7 @@ export default async function getBaseWebpackConfig(
             return prev
           }, [] as string[])
         : []),
-      'next/dist/pages/_app.js',
+      isEdgeServer ? 'next/dist/esm/pages/_app.js' : 'next/dist/pages/_app.js',
     ]
     customAppAliases[`${PAGES_DIR_ALIAS}/_error`] = [
       ...(pagesDir
@@ -804,7 +802,9 @@ export default async function getBaseWebpackConfig(
             return prev
           }, [] as string[])
         : []),
-      'next/dist/pages/_error.js',
+      isEdgeServer
+        ? 'next/dist/esm/pages/_error.js'
+        : 'next/dist/pages/_error.js',
     ]
     customDocumentAliases[`${PAGES_DIR_ALIAS}/_document`] = [
       ...(pagesDir
@@ -813,7 +813,9 @@ export default async function getBaseWebpackConfig(
             return prev
           }, [] as string[])
         : []),
-      `next/dist/pages/_document.js`,
+      isEdgeServer
+        ? `next/dist/esm/pages/_document.js`
+        : `next/dist/pages/_document.js`,
     ]
   }
 

packages/next/build/webpack/loaders/next-app-loader.ts

@@ -120,8 +120,9 @@ const nextAppLoader: webpack.LoaderDefinitionFunction<{
   appDir: string
   appPaths: string[] | null
   pageExtensions: string[]
+  nextRuntime: string
 }> = async function nextAppLoader() {
-  const { name, appDir, appPaths, pagePath, pageExtensions } =
+  const { name, appDir, appPaths, pagePath, pageExtensions, nextRuntime } =
     this.getOptions() || {}
 
   const buildInfo = getModuleBuildInfo((this as any)._module)
@@ -179,23 +180,24 @@ const nextAppLoader: webpack.LoaderDefinitionFunction<{
     resolveParallelSegments,
   })
 
+  const rootDistFolder = nextRuntime === 'edge' ? 'next/dist/esm' : 'next/dist'
   const result = `
     export ${treeCode}
 
-    export const AppRouter = require('next/dist/client/components/app-router.client.js').default
-    export const LayoutRouter = require('next/dist/client/components/layout-router.client.js').default
-    export const RenderFromTemplateContext = require('next/dist/client/components/render-from-template-context.client.js').default
+    export const AppRouter = require('${rootDistFolder}/client/components/app-router.client.js').default
+    export const LayoutRouter = require('${rootDistFolder}/client/components/layout-router.client.js').default
+    export const RenderFromTemplateContext = require('${rootDistFolder}/client/components/render-from-template-context.client.js').default
     export const HotReloader = ${
       // Disable HotReloader component in production
       this.mode === 'development'
-        ? `require('next/dist/client/components/hot-reloader.client.js').default`
+        ? `require('${rootDistFolder}/client/components/hot-reloader.client.js').default`
         : 'null'
     }
 
-    export const staticGenerationAsyncStorage = require('next/dist/client/components/static-generation-async-storage.js').staticGenerationAsyncStorage
-    export const requestAsyncStorage = require('next/dist/client/components/request-async-storage.js').requestAsyncStorage
+    export const staticGenerationAsyncStorage = require('${rootDistFolder}/client/components/static-generation-async-storage.js').staticGenerationAsyncStorage
+    export const requestAsyncStorage = require('${rootDistFolder}/client/components/request-async-storage.js').requestAsyncStorage
 
-    export const serverHooks = require('next/dist/client/components/hooks-server-context.js')
+    export const serverHooks = require('${rootDistFolder}/client/components/hooks-server-context.js')
 
     export const renderToReadableStream = require('next/dist/compiled/react-server-dom-webpack/writer.browser.server').renderToReadableStream
     export const __next_app_webpack_require__ = __webpack_require__

packages/next/build/webpack/loaders/next-edge-ssr-loader/index.ts

@@ -18,6 +18,18 @@ export type EdgeSSRLoaderQuery = {
   hasFontLoaders: boolean
 }
 
+/*
+For pages SSR'd at the edge, we bundle them with the ESM version of Next in order to
+benefit from the better tree-shaking and thus, smaller bundle sizes.
+
+The absolute paths for _app, _error and _document, used in this loader, link to the regular CJS modules.
+They are generated in `createPagesMapping` where we don't have access to `isEdgeRuntime`,
+so we have to do it here. It's not that bad because it keeps all references to ESM modules magic in this place.
+*/
+function swapDistFolderWithEsmDistFolder(path: string) {
+  return path.replace('next/dist/pages', 'next/dist/esm/pages')
+}
+
 export default async function edgeSSRLoader(this: any) {
   const {
     dev,
@@ -54,9 +66,18 @@ export default async function edgeSSRLoader(this: any) {
   }
 
   const stringifiedPagePath = stringifyRequest(this, absolutePagePath)
-  const stringifiedAppPath = stringifyRequest(this, absoluteAppPath)
-  const stringifiedErrorPath = stringifyRequest(this, absoluteErrorPath)
-  const stringifiedDocumentPath = stringifyRequest(this, absoluteDocumentPath)
+  const stringifiedAppPath = stringifyRequest(
+    this,
+    swapDistFolderWithEsmDistFolder(absoluteAppPath)
+  )
+  const stringifiedErrorPath = stringifyRequest(
+    this,
+    swapDistFolderWithEsmDistFolder(absoluteErrorPath)
+  )
+  const stringifiedDocumentPath = stringifyRequest(
+    this,
+    swapDistFolderWithEsmDistFolder(absoluteDocumentPath)
+  )
   const stringified500Path = absolute500Path
     ? stringifyRequest(this, absolute500Path)
     : null
@@ -67,8 +88,8 @@ export default async function edgeSSRLoader(this: any) {
   )}`
 
   const transformed = `
-    import { adapter, enhanceGlobals } from 'next/dist/server/web/adapter'
-    import { getRender } from 'next/dist/build/webpack/loaders/next-edge-ssr-loader/render'
+    import { adapter, enhanceGlobals } from 'next/dist/esm/server/web/adapter'
+    import { getRender } from 'next/dist/esm/build/webpack/loaders/next-edge-ssr-loader/render'
 
     enhanceGlobals()
 
@@ -77,7 +98,7 @@ export default async function edgeSSRLoader(this: any) {
       isAppDir
         ? `
       const Document = null
-      const appRenderToHTML = require('next/dist/server/app-render').renderToHTMLOrFlight
+      const appRenderToHTML = require('next/dist/esm/server/app-render').renderToHTMLOrFlight
       const pagesRenderToHTML = null
       const pageMod = require(${JSON.stringify(pageModPath)})
       const appMod = null
@@ -87,7 +108,7 @@ export default async function edgeSSRLoader(this: any) {
         : `
       const Document = require(${stringifiedDocumentPath}).default
       const appRenderToHTML = null
-      const pagesRenderToHTML = require('next/dist/server/render').renderToHTML
+      const pagesRenderToHTML = require('next/dist/esm/server/render').renderToHTML
       const pageMod = require(${stringifiedPagePath})
       const appMod = require(${stringifiedAppPath})
       const errorMod = require(${stringifiedErrorPath})

packages/next/build/webpack/loaders/next-edge-ssr-loader/render.ts

@@ -1,4 +1,5 @@
 import type { NextConfig } from '../../../../server/config-shared'
+
 import type { DocumentType, AppType } from '../../../../shared/lib/utils'
 import type { BuildManifest } from '../../../../server/get-page-files'
 import type { ReactLoadableManifest } from '../../../../server/load-components'

packages/next/build/webpack/plugins/flight-client-entry-plugin.ts

@@ -307,9 +307,19 @@ export class FlightClientEntryPlugin {
       modules: clientComponentImports,
       server: false,
     }
-    const clientLoader = `next-flight-client-entry-loader?${stringify(
-      loaderOptions
-    )}!`
+
+    // For the client entry, we always use the CJS build of Next.js. If the
+    // server is using the ESM build (when using the Edge runtime), we need to
+    // replace them.
+    const clientLoader = `next-flight-client-entry-loader?${stringify({
+      modules: this.isEdgeServer
+        ? clientComponentImports.map((importPath) =>
+            importPath.replace('next/dist/esm/', 'next/dist/')
+          )
+        : clientComponentImports,
+      server: false,
+    })}!`
+
     const clientSSRLoader = `next-flight-client-entry-loader?${stringify({
       ...loaderOptions,
       server: true,

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

@@ -56,6 +56,9 @@ export type FlightManifest = {
   __ssr_module_mapping__: {
     [moduleId: string]: ManifestNode
   }
+  __edge_ssr_module_mapping__: {
+    [moduleId: string]: ManifestNode
+  }
 } & {
   [modulePath: string]: ManifestNode
 }
@@ -141,6 +144,7 @@ export class FlightManifestPlugin {
   ) {
     const manifest: FlightManifest = {
       __ssr_module_mapping__: {},
+      __edge_ssr_module_mapping__: {},
     }
     const dev = this.dev
     const fontLoaderTargets = this.fontLoaderTargets
@@ -196,6 +200,7 @@ export class FlightManifestPlugin {
 
         const moduleExports = manifest[resource] || {}
         const moduleIdMapping = manifest.__ssr_module_mapping__
+        const edgeModuleIdMapping = manifest.__edge_ssr_module_mapping__
 
         // Note that this isn't that reliable as webpack is still possible to assign
         // additional queries to make sure there's no conflict even using the `named`
@@ -304,10 +309,25 @@ export class FlightManifestPlugin {
             ...moduleExports[name],
             id: ssrNamedModuleId,
           }
+
+          edgeModuleIdMapping[id] = edgeModuleIdMapping[id] || {}
+          edgeModuleIdMapping[id][name] = {
+            ...moduleExports[name],
+            id: ssrNamedModuleId.replace(/\/next\/dist\//, '/next/dist/esm/'),
+          }
         })
 
         manifest[resource] = moduleExports
+
+        // The client compiler will always use the CJS Next.js build, so here we
+        // also add the mapping for the ESM build (Edge runtime) to consume.
+        if (/\/next\/dist\//.test(resource)) {
+          manifest[resource.replace(/\/next\/dist\//, '/next/dist/esm/')] =
+            moduleExports
+        }
+
         manifest.__ssr_module_mapping__ = moduleIdMapping
+        manifest.__edge_ssr_module_mapping__ = edgeModuleIdMapping
       }
 
       chunkGroup.chunks.forEach((chunk: webpack.Chunk) => {

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

@@ -110,11 +110,15 @@ function findFeatureInModule(module: Module): Feature | undefined {
  * dependency.
  */
 function findUniqueOriginModulesInConnections(
-  connections: Connection[]
+  connections: Connection[],
+  originModule: Module
 ): Set<unknown> {
   const originModules = new Set()
   for (const connection of connections) {
-    if (!originModules.has(connection.originModule)) {
+    if (
+      !originModules.has(connection.originModule) &&
+      connection.originModule !== originModule
+    ) {
       originModules.add(connection.originModule)
     }
   }
@@ -161,8 +165,10 @@ export class TelemetryPlugin implements webpack.WebpackPluginInstance {
               const connections = (
                 compilation as any
               ).moduleGraph.getIncomingConnections(module)
-              const originModules =
-                findUniqueOriginModulesInConnections(connections)
+              const originModules = findUniqueOriginModulesInConnections(
+                connections,
+                module
+              )
               this.usageTracker.get(feature)!.invocationCount =
                 originModules.size
             }

packages/next/client.js

@@ -1 +1,4 @@
-module.exports = require('./dist/client/index')
+module.exports =
+  process.env.NEXT_RUNTIME === 'edge'
+    ? require('./dist/esm/client/index')
+    : require('./dist/client/index')

packages/next/config.js

@@ -1 +1,4 @@
-module.exports = require('./dist/shared/lib/runtime-config')
+module.exports =
+  process.env.NEXT_RUNTIME === 'edge'
+    ? require('./dist/esm/shared/lib/runtime-config')
+    : require('./dist/shared/lib/runtime-config')

packages/next/constants.js

@@ -1 +1,4 @@
-module.exports = require('./dist/shared/lib/constants')
+module.exports =
+  process.env.NEXT_RUNTIME === 'edge'
+    ? require('./dist/esm/shared/lib/constants')
+    : require('./dist/shared/lib/constants')

packages/next/document.js

@@ -1 +1,4 @@
-module.exports = require('./dist/pages/_document')
+module.exports =
+  process.env.NEXT_RUNTIME === 'edge'
+    ? require('./dist/esm/pages/_document')
+    : require('./dist/pages/_document')

packages/next/dynamic.js

@@ -1 +1,4 @@
-module.exports = require('./dist/shared/lib/dynamic')
+module.exports =
+  process.env.NEXT_RUNTIME === 'edge'
+    ? require('./dist/esm/shared/lib/dynamic')
+    : require('./dist/shared/lib/dynamic')

packages/next/error.js

@@ -1 +1,4 @@
-module.exports = require('./dist/pages/_error')
+module.exports =
+  process.env.NEXT_RUNTIME === 'edge'
+    ? require('./dist/esm/pages/_error')
+    : require('./dist/pages/_error')

packages/next/head.js

@@ -1 +1,4 @@
-module.exports = require('./dist/shared/lib/head')
+module.exports =
+  process.env.NEXT_RUNTIME === 'edge'
+    ? require('./dist/esm/shared/lib/head')
+    : require('./dist/shared/lib/head')

packages/next/image.js

@@ -1 +1,4 @@
-module.exports = require('./dist/client/image')
+module.exports =
+  process.env.NEXT_RUNTIME === 'edge'
+    ? require('./dist/esm/client/image')
+    : require('./dist/client/image')

packages/next/link.js

@@ -1 +1,4 @@
-module.exports = require('./dist/client/link')
+module.exports =
+  process.env.NEXT_RUNTIME === 'edge'
+    ? require('./dist/esm/client/link')
+    : require('./dist/client/link')

packages/next/pages/_app.tsx

@@ -1,6 +1,6 @@
 import React from 'react'
-import {
-  loadGetInitialProps,
+
+import type {
   AppContextType,
   AppInitialProps,
   AppPropsType,
@@ -9,6 +9,8 @@ import {
 } from '../shared/lib/utils'
 import type { Router } from '../client/router'
 
+import { loadGetInitialProps } from '../shared/lib/utils'
+
 export { AppInitialProps, AppType }
 
 export { NextWebVitalsMetric }

packages/next/router.js

@@ -1 +1,4 @@
-module.exports = require('./dist/client/router')
+module.exports =
+  process.env.NEXT_RUNTIME === 'edge'
+    ? require('./dist/esm/client/router')
+    : require('./dist/client/router')

packages/next/script.js

@@ -1 +1,4 @@
-module.exports = require('./dist/client/script')
+module.exports =
+  process.env.NEXT_RUNTIME === 'edge'
+    ? require('./dist/esm/client/script')
+    : require('./dist/client/script')