Prefetch SSG Data

packages/next/build/index.ts

@@ -1,5 +1,6 @@
 import chalk from 'chalk'
 import ciEnvironment from 'ci-info'
+import devalue from 'devalue'
 import findUp from 'find-up'
 import fs from 'fs'
 import Worker from 'jest-worker'
@@ -11,10 +12,10 @@ import { promisify } from 'util'
 import formatWebpackMessages from '../client/dev/error-overlay/format-webpack-messages'
 import checkCustomRoutes, {
   getRedirectStatus,
-  RouteType,
+  Header,
   Redirect,
   Rewrite,
-  Header,
+  RouteType,
 } from '../lib/check-custom-routes'
 import { PUBLIC_DIR_MIDDLEWARE_CONFLICT } from '../lib/constants'
 import { findPagesDir } from '../lib/find-pages-dir'
@@ -23,6 +24,7 @@ import { recursiveReadDir } from '../lib/recursive-readdir'
 import { verifyTypeScriptSetup } from '../lib/verifyTypeScriptSetup'
 import {
   BUILD_MANIFEST,
+  CLIENT_STATIC_FILES_PATH,
   EXPORT_DETAIL,
   EXPORT_MARKER,
   PAGES_MANIFEST,
@@ -726,6 +728,14 @@ export default async function build(dir: string, conf = null): Promise<void> {
       JSON.stringify(prerenderManifest),
       'utf8'
     )
+
+    generateClientSsgManifest(prerenderManifest, { distDir, buildId })
+  } else {
+    // Generate empty version if not used
+    generateClientSsgManifest(
+      { version: 0, routes: {}, dynamicRoutes: {} },
+      { distDir, buildId }
+    )
   }
 
   await fsWriteFile(
@@ -824,3 +834,33 @@ export default async function build(dir: string, conf = null): Promise<void> {
 
   await telemetry.flush()
 }
+
+function generateClientSsgManifest(
+  prerenderManifest: PrerenderManifest,
+  { buildId, distDir }: { buildId: string; distDir: string }
+) {
+  const regexOperatorsRegex = /[|\\{}()[\]^$+*?.-]/g
+  const ssgMatchers: RegExp[] = []
+  Object.keys(prerenderManifest.routes).forEach(route =>
+    ssgMatchers.push(
+      new RegExp('^' + route.replace(regexOperatorsRegex, '\\$&') + '$')
+    )
+  )
+  Object.values(prerenderManifest.dynamicRoutes).forEach(entry =>
+    ssgMatchers.push(new RegExp(entry.routeRegex))
+  )
+
+  const clientSsgManifestPaths = [
+    '_ssgManifest.js',
+    '_ssgManifest.module.js',
+  ].map(f => path.join(`${CLIENT_STATIC_FILES_PATH}/${buildId}`, f))
+  const clientSsgManifestContent = `self.__SSG_MANIFEST = ${devalue(
+    ssgMatchers
+  )};self.__SSG_MANIFEST_CB && self.__SSG_MANIFEST_CB()`
+  clientSsgManifestPaths.forEach(clientSsgManifestPath =>
+    fs.writeFileSync(
+      path.join(distDir, clientSsgManifestPath),
+      clientSsgManifestContent
+    )
+  )
+}

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

@@ -149,6 +149,17 @@ export default class BuildManifestPlugin {
           }
         }
 
+        // Add the runtime ssg manifest file (generated later in the build) as
+        // a dependency for the app.
+        assetMap.pages['/_app'].push(
+          `${CLIENT_STATIC_FILES_PATH}/${this.buildId}/_ssgManifest.js`
+        )
+        if (this.modern) {
+          assetMap.pages['/_app'].push(
+            `${CLIENT_STATIC_FILES_PATH}/${this.buildId}/_ssgManifest.module.js`
+          )
+        }
+
         assetMap.pages = Object.keys(assetMap.pages)
           .sort()
           // eslint-disable-next-line

packages/next/client/link.tsx

@@ -127,14 +127,15 @@ class Link extends Component<LinkProps> {
     this.cleanUpListeners()
   }
 
-  getHref() {
+  getHrefs(): { href: string; as: string } {
     const { pathname } = window.location
-    const { href: parsedHref } = this.formatUrls(this.props.href, this.props.as)
-    return resolve(pathname, parsedHref)
+    const { href, as } = this.formatUrls(this.props.href, this.props.as)
+    const parsedHref = resolve(pathname, href)
+    return { href: parsedHref, as: as ? resolve(pathname, as) : parsedHref }
   }
 
   handleRef(ref: Element) {
-    const isPrefetched = prefetched[this.getHref()]
+    const isPrefetched = prefetched[this.getHrefs().href]
     if (this.p && IntersectionObserver && ref && ref.tagName) {
       this.cleanUpListeners()
 
@@ -204,8 +205,11 @@ class Link extends Component<LinkProps> {
   prefetch() {
     if (!this.p || typeof window === 'undefined') return
     // Prefetch the JSON page if asked (only in the client)
-    const href = this.getHref()
+    const { href, as } = this.getHrefs()
     Router.prefetch(href)
+    // Cast to any because this is a private method, might be public in the
+    // future
+    ;(Router as any).prefetchAs(as)
     prefetched[href] = true
   }
 

packages/next/client/page-loader.js

@@ -56,12 +56,18 @@ export default class PageLoader {
         if (window.__BUILD_MANIFEST) {
           resolve(window.__BUILD_MANIFEST)
         } else {
-          window.__BUILD_MANIFEST_CB = () => {
-            resolve(window.__BUILD_MANIFEST)
-          }
+          window.__BUILD_MANIFEST_CB = () => resolve(window.__BUILD_MANIFEST)
         }
       })
     }
+    /** @type {Promise<RegExp[]>} */
+    this.promisedSsgManifest = new Promise(resolve => {
+      if (window.__SSG_MANIFEST) {
+        resolve(window.__SSG_MANIFEST)
+      } else {
+        window.__SSG_MANIFEST_CB = () => resolve(window.__SSG_MANIFEST)
+      }
+    })
   }
 
   // Returns a promise for the dependencies for a particular route
@@ -76,6 +82,22 @@ export default class PageLoader {
     )
   }
 
+  /** @param {string} asPath */
+  prefetchAs(asPath) {
+    asPath = normalizeRoute(asPath)
+    return this.promisedSsgManifest.then(
+      m =>
+        m.some(r => r.test(asPath)) &&
+        appendLink(
+          `${this.assetPrefix}/_next/${this.buildId}/${
+            asPath === '/' ? '/index' : asPath
+          }.json`,
+          relPrefetch,
+          'fetch'
+        )
+    )
+  }
+
   loadPage(route) {
     return this.loadPageScript(route).then(v => v.page)
   }
@@ -206,6 +228,10 @@ export default class PageLoader {
     register()
   }
 
+  /**
+   * @param {string} route
+   * @param {boolean} [isDependency]
+   */
   prefetch(route, isDependency) {
     // https://github.com/GoogleChromeLabs/quicklink/blob/453a661fa1fa940e2d2e044452398e38c67a98fb/src/index.mjs#L115-L118
     // License: Apache 2.0
@@ -215,6 +241,7 @@ export default class PageLoader {
       if (cn.saveData || /2g/.test(cn.effectiveType)) return Promise.resolve()
     }
 
+    /** @type {string} */
     let url
     if (isDependency) {
       url = route

packages/next/next-server/lib/router/router.ts

@@ -620,6 +620,16 @@ export default class Router implements BaseRouter {
     })
   }
 
+  prefetchAs(url: string): Promise<void> {
+    return new Promise((resolve, reject) => {
+      const { pathname, protocol } = parse(url)
+      if (!pathname || protocol || process.env.NODE_ENV !== 'production') {
+        return
+      }
+      this.pageLoader.prefetchAs(pathname).then(resolve, reject)
+    })
+  }
+
   async fetchComponent(route: string): Promise<ComponentType> {
     let cancelled = false
     const cancel = (this.clc = () => {

packages/next/pages/_document.tsx

@@ -45,7 +45,7 @@ function getOptionalModernScriptVariant(path: string) {
 }
 
 function isLowPriority(file: string) {
-  return file.includes('_buildManifest')
+  return file.includes('_buildManifest') || file.includes('_ssgManifest')
 }
 
 /**