Allow pages to be async modules to enable top-level-await (vercel#17590)

Co-authored-by: JJ Kasper <jj@jjsweb.site>
Co-authored-by: kodiakhq[bot] <49736102+kodiakhq[bot]@users.noreply.github.com>

.eslintignore

@@ -13,4 +13,5 @@ packages/next-codemod/transforms/__testfixtures__/**/*
 packages/next-codemod/transforms/__tests__/**/*
 packages/next-codemod/**/*.js
 packages/next-codemod/**/*.d.ts
-packages/next-env/**/*.d.ts
+packages/next-env/**/*.d.ts
+test/integration/async-modules/**

.github/workflows/build_test_deploy.yml

@@ -113,6 +113,7 @@ jobs:
       - run: yarn install --check-files
       - run: node run-tests.js test/integration/production/test/index.test.js
       - run: node run-tests.js test/integration/basic/test/index.test.js
+      - run: node run-tests.js test/integration/async-modules/test/index.test.js
       - run: node run-tests.js test/integration/font-optimization/test/index.test.js
       - run: node run-tests.js test/acceptance/*
 

packages/next/build/index.ts

@@ -531,7 +531,7 @@ export default async function build(
         const serverBundle = getPagePath(page, distDir, isLikeServerless)
 
         if (customAppGetInitialProps === undefined) {
-          customAppGetInitialProps = hasCustomGetInitialProps(
+          customAppGetInitialProps = await hasCustomGetInitialProps(
             isLikeServerless
               ? serverBundle
               : getPagePath('/_app', distDir, isLikeServerless),

packages/next/build/utils.ts

@@ -704,21 +704,21 @@ export async function isPageStatic(
 }> {
   try {
     require('../next-server/lib/runtime-config').setConfig(runtimeEnvConfig)
-    const mod = require(serverBundle)
-    const Comp = mod.default || mod
+    const mod = await require(serverBundle)
+    const Comp = await (mod.default || mod)
 
     if (!Comp || !isValidElementType(Comp) || typeof Comp === 'string') {
       throw new Error('INVALID_DEFAULT_EXPORT')
     }
 
     const hasGetInitialProps = !!(Comp as any).getInitialProps
-    const hasStaticProps = !!mod.getStaticProps
-    const hasStaticPaths = !!mod.getStaticPaths
-    const hasServerProps = !!mod.getServerSideProps
-    const hasLegacyServerProps = !!mod.unstable_getServerProps
-    const hasLegacyStaticProps = !!mod.unstable_getStaticProps
-    const hasLegacyStaticPaths = !!mod.unstable_getStaticPaths
-    const hasLegacyStaticParams = !!mod.unstable_getStaticParams
+    const hasStaticProps = !!(await mod.getStaticProps)
+    const hasStaticPaths = !!(await mod.getStaticPaths)
+    const hasServerProps = !!(await mod.getServerSideProps)
+    const hasLegacyServerProps = !!(await mod.unstable_getServerProps)
+    const hasLegacyStaticProps = !!(await mod.unstable_getStaticProps)
+    const hasLegacyStaticPaths = !!(await mod.unstable_getStaticPaths)
+    const hasLegacyStaticParams = !!(await mod.unstable_getStaticParams)
 
     if (hasLegacyStaticParams) {
       throw new Error(
@@ -804,19 +804,20 @@ export async function isPageStatic(
   }
 }
 
-export function hasCustomGetInitialProps(
+export async function hasCustomGetInitialProps(
   bundle: string,
   runtimeEnvConfig: any,
   checkingApp: boolean
-): boolean {
+): Promise<boolean> {
   require('../next-server/lib/runtime-config').setConfig(runtimeEnvConfig)
   let mod = require(bundle)
 
   if (checkingApp) {
-    mod = mod._app || mod.default || mod
+    mod = (await mod._app) || mod.default || mod
   } else {
     mod = mod.default || mod
   }
+  mod = await mod
   return mod.getInitialProps !== mod.origGetInitialProps
 }
 

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

@@ -339,7 +339,7 @@ const nextServerlessLoader: loader.Loader = function () {
               : `{}`
           }
 
-          const resolver = require('${absolutePagePath}')
+          const resolver = await require('${absolutePagePath}')
           await apiResolver(
             req,
             res,
@@ -386,35 +386,57 @@ const nextServerlessLoader: loader.Loader = function () {
     const {sendPayload} = require('next/dist/next-server/server/send-payload');
     const buildManifest = require('${buildManifest}');
     const reactLoadableManifest = require('${reactLoadableManifest}');
-    const Document = require('${absoluteDocumentPath}').default;
-    const Error = require('${absoluteErrorPath}').default;
-    const App = require('${absoluteAppPath}').default;
+
+    const appMod = require('${absoluteAppPath}')
+    let App = appMod.default || appMod.then && appMod.then(mod => mod.default);
 
     ${dynamicRouteImports}
     ${rewriteImports}
 
-    const ComponentInfo = require('${absolutePagePath}')
+    const compMod = require('${absolutePagePath}')
 
-    const Component = ComponentInfo.default
+    let Component = compMod.default || compMod.then && compMod.then(mod => mod.default)
     export default Component
-    export const unstable_getStaticParams = ComponentInfo['unstable_getStaticParam' + 's']
-    export const getStaticProps = ComponentInfo['getStaticProp' + 's']
-    export const getStaticPaths = ComponentInfo['getStaticPath' + 's']
-    export const getServerSideProps = ComponentInfo['getServerSideProp' + 's']
+    export let getStaticProps = compMod['getStaticProp' + 's'] || compMod.then && compMod.then(mod => mod['getStaticProp' + 's'])
+    export let getStaticPaths = compMod['getStaticPath' + 's'] || compMod.then && compMod.then(mod => mod['getStaticPath' + 's'])
+    export let getServerSideProps = compMod['getServerSideProp' + 's'] || compMod.then && compMod.then(mod => mod['getServerSideProp' + 's'])
 
     // kept for detecting legacy exports
-    export const unstable_getStaticProps = ComponentInfo['unstable_getStaticProp' + 's']
-    export const unstable_getStaticPaths = ComponentInfo['unstable_getStaticPath' + 's']
-    export const unstable_getServerProps = ComponentInfo['unstable_getServerProp' + 's']
+    export const unstable_getStaticParams = compMod['unstable_getStaticParam' + 's'] || compMod.then && compMod.then(mod => mod['unstable_getStaticParam' + 's'])
+    export const unstable_getStaticProps = compMod['unstable_getStaticProp' + 's'] || compMod.then && compMod.then(mod => mod['unstable_getStaticProp' + 's'])
+    export const unstable_getStaticPaths = compMod['unstable_getStaticPath' + 's'] || compMod.then && compMod.then(mod => mod['unstable_getStaticPath' + 's'])
+    export const unstable_getServerProps = compMod['unstable_getServerProp' + 's'] || compMod.then && compMod.then(mod => mod['unstable_getServerProp' + 's'])
 
     ${dynamicRouteMatcher}
     ${defaultRouteRegex}
     ${normalizeDynamicRouteParams}
     ${handleRewrites}
 
-    export const config = ComponentInfo['confi' + 'g'] || {}
+    export let config = compMod['confi' + 'g'] || (compMod.then && compMod.then(mod => mod['confi' + 'g'])) || {}
     export const _app = App
     export async function renderReqToHTML(req, res, renderMode, _renderOpts, _params) {
+      let Document
+      let Error
+      ;[
+        getStaticProps,
+        getServerSideProps,
+        getStaticPaths,
+        Component,
+        App,
+        config,
+        { default: Document },
+        { default: Error }
+      ] = await Promise.all([
+        getStaticProps,
+        getServerSideProps,
+        getStaticPaths,
+        Component,
+        App,
+        config,
+        require('${absoluteDocumentPath}'),
+        require('${absoluteErrorPath}')
+      ])
+
       const fromExport = renderMode === 'export' || renderMode === true;
       const nextStartMode = renderMode === 'passthrough'
 

packages/next/client/page-loader.ts

@@ -340,9 +340,9 @@ export default class PageLoader {
 
   // This method if called by the route code.
   registerPage(route: string, regFn: () => any) {
-    const register = (styleSheets: StyleSheetTuple[]) => {
+    const register = async (styleSheets: StyleSheetTuple[]) => {
       try {
-        const mod = regFn()
+        const mod = await regFn()
         const pageData: PageCacheEntry = {
           page: mod.default || mod,
           mod,

packages/next/next-server/server/load-components.ts

@@ -41,20 +41,27 @@ export async function loadComponents(
 ): Promise<LoadComponentsReturnType> {
   if (serverless) {
     const Component = await requirePage(pathname, distDir, serverless)
-    const { getStaticProps, getStaticPaths, getServerSideProps } = Component
+    let { getStaticProps, getStaticPaths, getServerSideProps } = Component
+
+    getStaticProps = await getStaticProps
+    getStaticPaths = await getStaticPaths
+    getServerSideProps = await getServerSideProps
+    const pageConfig = (await Component.config) || {}
 
     return {
       Component,
-      pageConfig: Component.config || {},
+      pageConfig,
       getStaticProps,
       getStaticPaths,
       getServerSideProps,
     } as LoadComponentsReturnType
   }
 
-  const DocumentMod = requirePage('/_document', distDir, serverless)
-  const AppMod = requirePage('/_app', distDir, serverless)
-  const ComponentMod = requirePage(pathname, distDir, serverless)
+  const [DocumentMod, AppMod, ComponentMod] = await Promise.all([
+    requirePage('/_document', distDir, serverless),
+    requirePage('/_app', distDir, serverless),
+    requirePage(pathname, distDir, serverless),
+  ])
 
   const [
     buildManifest,

packages/next/next-server/server/next-server.ts

@@ -866,7 +866,7 @@ export default class Server {
       throw err
     }
 
-    const pageModule = require(builtPagePath)
+    const pageModule = await require(builtPagePath)
     query = { ...query, ...params }
 
     if (!this.renderOpts.dev && this._isLikeServerless) {

test/integration/async-modules/next.config.js

@@ -0,0 +1,9 @@
+module.exports = {
+  // target: 'experimental-serverless-trace',
+  webpack: (config, options) => {
+    config.experiments = {
+      topLevelAwait: true,
+    }
+    return config
+  },
+}

test/integration/async-modules/pages/404.jsx

@@ -0,0 +1,5 @@
+const content = await Promise.resolve("hi y'all")
+
+export default function Custom404() {
+  return <h1 id="content-404">{content}</h1>
+}

test/integration/async-modules/pages/_app.jsx

@@ -0,0 +1,5 @@
+const appValue = await Promise.resolve('hello')
+
+export default function MyApp({ Component, pageProps }) {
+  return <Component {...pageProps} appValue={appValue} />
+}

test/integration/async-modules/pages/_document.jsx

@@ -0,0 +1,25 @@
+import Document, { Html, Head, Main, NextScript } from 'next/document'
+
+const docValue = await Promise.resolve('doc value')
+
+class MyDocument extends Document {
+  static async getInitialProps(ctx) {
+    const initialProps = await Document.getInitialProps(ctx)
+    return { ...initialProps, docValue }
+  }
+
+  render() {
+    return (
+      <Html>
+        <Head />
+        <body>
+          <div id="doc-value">{this.props.docValue}</div>
+          <Main />
+          <NextScript />
+        </body>
+      </Html>
+    )
+  }
+}
+
+export default MyDocument

test/integration/async-modules/pages/_error.jsx

@@ -0,0 +1,7 @@
+const errorContent = await Promise.resolve('hello error')
+
+function Error({ statusCode }) {
+  return <p id="content-error">{errorContent}</p>
+}
+
+export default Error

test/integration/async-modules/pages/api/hello.js

@@ -0,0 +1,5 @@
+const value = await Promise.resolve(42)
+
+export default function (req, res) {
+  res.json({ value })
+}

test/integration/async-modules/pages/config.jsx

@@ -0,0 +1,22 @@
+export const config = {
+  amp: true,
+}
+
+await Promise.resolve('tadaa')
+
+export default function Config() {
+  const date = new Date()
+  return (
+    <div>
+      <amp-timeago
+        id="amp-timeago"
+        width="0"
+        height="15"
+        datetime={date.toJSON()}
+        layout="responsive"
+      >
+        fail
+      </amp-timeago>
+    </div>
+  )
+}

test/integration/async-modules/pages/gsp.jsx

@@ -0,0 +1,15 @@
+const gspValue = await Promise.resolve(42)
+
+export async function getStaticProps() {
+  return {
+    props: { gspValue },
+  }
+}
+
+export default function Index({ gspValue }) {
+  return (
+    <main>
+      <div id="gsp-value">{gspValue}</div>
+    </main>
+  )
+}

test/integration/async-modules/pages/gssp.jsx

@@ -0,0 +1,15 @@
+const gsspValue = await Promise.resolve(42)
+
+export async function getServerSideProps() {
+  return {
+    props: { gsspValue },
+  }
+}
+
+export default function Index({ gsspValue }) {
+  return (
+    <main>
+      <div id="gssp-value">{gsspValue}</div>
+    </main>
+  )
+}

test/integration/async-modules/pages/index.jsx

@@ -0,0 +1,10 @@
+const value = await Promise.resolve(42)
+
+export default function Index({ appValue }) {
+  return (
+    <main>
+      <div id="app-value">{appValue}</div>
+      <div id="page-value">{value}</div>
+    </main>
+  )
+}

test/integration/async-modules/pages/make-error.jsx

@@ -0,0 +1,7 @@
+export async function getServerSideProps() {
+  throw new Error('BOOM')
+}
+
+export default function Page() {
+  return <div>hello</div>
+}