Per-page runtime (#35011)

Partially implements #31317 and #31506. There're also some trade-offs made with this PR: since we can't know if a certain runtime will be used or not beforehand, we have to start both runtime compilers (Node.js and Edge) and then generate entrypoints correspondingly.

Note that with this PR, the global runtime is still required to use the per-page runtime.

## Bug

- [ ] Related issues linked using `fixes #number`
- [x] 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 by running `yarn lint`

packages/next/build/entries.ts

@@ -39,11 +39,11 @@ export function createPagesMapping(
   {
     isDev,
     hasServerComponents,
-    runtime,
+    globalRuntime,
   }: {
     isDev: boolean
     hasServerComponents: boolean
-    runtime?: 'nodejs' | 'edge'
+    globalRuntime?: 'nodejs' | 'edge'
   }
 ): PagesMapping {
   const previousPages: PagesMapping = {}
@@ -83,7 +83,7 @@ export function createPagesMapping(
   // we alias these in development and allow webpack to
   // allow falling back to the correct source file so
   // that HMR can work properly when a file is added/removed
-  const documentPage = `_document${runtime ? '-concurrent' : ''}`
+  const documentPage = `_document${globalRuntime ? '-concurrent' : ''}`
   if (isDev) {
     pages['/_app'] = `${PAGES_DIR_ALIAS}/_app`
     pages['/_error'] = `${PAGES_DIR_ALIAS}/_error`
@@ -103,68 +103,108 @@ type Entrypoints = {
   edgeServer: webpack5.EntryObject
 }
 
-export async function getPageRuntime(pageFilePath: string) {
-  let pageRuntime: string | undefined = undefined
-  const pageContent = await fs.promises.readFile(pageFilePath, {
-    encoding: 'utf8',
-  })
-  // branch prunes for entry page without runtime option
-  if (pageContent.includes('runtime')) {
-    const { body } = await parse(pageContent, {
-      filename: pageFilePath,
-      isModule: true,
+const cachedPageRuntimeConfig = new Map<
+  string,
+  [number, 'nodejs' | 'edge' | undefined]
+>()
+
+// @TODO: We should limit the maximum concurrency of this function as there
+// could be thousands of pages existing.
+export async function getPageRuntime(
+  pageFilePath: string,
+  globalRuntimeFallback?: 'nodejs' | 'edge'
+): Promise<'nodejs' | 'edge' | undefined> {
+  const cached = cachedPageRuntimeConfig.get(pageFilePath)
+  if (cached) {
+    return cached[1]
+  }
+
+  let pageContent: string
+  try {
+    pageContent = await fs.promises.readFile(pageFilePath, {
+      encoding: 'utf8',
     })
-    body.some((node: any) => {
-      const { type, declaration } = node
-      const valueNode = declaration?.declarations?.[0]
-      if (type === 'ExportDeclaration' && valueNode?.id?.value === 'config') {
-        const props = valueNode.init.properties
-        const runtimeKeyValue = props.find(
-          (prop: any) => prop.key.value === 'runtime'
-        )
-        const runtime = runtimeKeyValue?.value?.value
-        pageRuntime =
-          runtime === 'edge' || runtime === 'nodejs' ? runtime : pageRuntime
-        return true
+  } catch (err) {
+    return undefined
+  }
+
+  // When gSSP or gSP is used, this page requires an execution runtime. If the
+  // page config is not present, we fallback to the global runtime. Related
+  // discussion:
+  // https://github.com/vercel/next.js/discussions/34179
+  let isRuntimeRequired: boolean = false
+  let pageRuntime: 'nodejs' | 'edge' | undefined = undefined
+
+  // Since these configurations should always be static analyzable, we can
+  // skip these cases that "runtime" and "gSP", "gSSP" are not included in the
+  // source code.
+  if (/runtime|getStaticProps|getServerSideProps/.test(pageContent)) {
+    try {
+      const { body } = await parse(pageContent, {
+        filename: pageFilePath,
+        isModule: true,
+      })
+
+      for (const node of body) {
+        const { type, declaration } = node
+        if (type === 'ExportDeclaration') {
+          // `export const config`
+          const valueNode = declaration?.declarations?.[0]
+          if (valueNode?.id?.value === 'config') {
+            const props = valueNode.init.properties
+            const runtimeKeyValue = props.find(
+              (prop: any) => prop.key.value === 'runtime'
+            )
+            const runtime = runtimeKeyValue?.value?.value
+            pageRuntime =
+              runtime === 'edge' || runtime === 'nodejs' ? runtime : pageRuntime
+          } else if (declaration?.type === 'FunctionDeclaration') {
+            // `export function getStaticProps` and
+            // `export function getServerSideProps`
+            if (
+              declaration.identifier?.value === 'getStaticProps' ||
+              declaration.identifier?.value === 'getServerSideProps'
+            ) {
+              isRuntimeRequired = true
+            }
+          }
+        }
       }
-      return false
-    })
+    } catch (err) {}
+  }
+
+  if (!pageRuntime) {
+    if (isRuntimeRequired) {
+      pageRuntime = globalRuntimeFallback
+    } else {
+      // @TODO: Remove this branch to fully implement the RFC.
+      pageRuntime = globalRuntimeFallback
+    }
   }
 
+  cachedPageRuntimeConfig.set(pageFilePath, [Date.now(), pageRuntime])
   return pageRuntime
 }
 
-export async function createPagesRuntimeMapping(
-  pagesDir: string,
-  pages: PagesMapping
+export function invalidatePageRuntimeCache(
+  pageFilePath: string,
+  safeTime: number
 ) {
-  const pagesRuntime: Record<string, string> = {}
-
-  const promises = Object.keys(pages).map(async (page) => {
-    const absolutePagePath = pages[page]
-    const isReserved = isReservedPage(page)
-    if (!isReserved) {
-      const pageFilePath = join(
-        pagesDir,
-        absolutePagePath.replace(PAGES_DIR_ALIAS, '')
-      )
-      const runtime = await getPageRuntime(pageFilePath)
-      if (runtime) {
-        pagesRuntime[page] = runtime
-      }
-    }
-  })
-  return await Promise.all(promises)
+  const cached = cachedPageRuntimeConfig.get(pageFilePath)
+  if (cached && cached[0] < safeTime) {
+    cachedPageRuntimeConfig.delete(pageFilePath)
+  }
 }
 
-export function createEntrypoints(
+export async function createEntrypoints(
   pages: PagesMapping,
   target: 'server' | 'serverless' | 'experimental-serverless-trace',
   buildId: string,
   previewMode: __ApiPreviewProps,
   config: NextConfigComplete,
-  loadedEnvFiles: LoadedEnvFiles
-): Entrypoints {
+  loadedEnvFiles: LoadedEnvFiles,
+  pagesDir: string
+): Promise<Entrypoints> {
   const client: webpack5.EntryObject = {}
   const server: webpack5.EntryObject = {}
   const edgeServer: webpack5.EntryObject = {}
@@ -201,103 +241,109 @@ export function createEntrypoints(
   }
 
   const globalRuntime = config.experimental.runtime
-  const edgeRuntime = globalRuntime === 'edge'
 
-  Object.keys(pages).forEach((page) => {
-    const absolutePagePath = pages[page]
-    const bundleFile = normalizePagePath(page)
-    const isApiRoute = page.match(API_ROUTE)
-
-    const clientBundlePath = posix.join('pages', bundleFile)
-    const serverBundlePath = posix.join('pages', bundleFile)
-
-    const isLikeServerless = isTargetLikeServerless(target)
-    const isReserved = isReservedPage(page)
-    const isCustomError = isCustomErrorPage(page)
-    const isFlight = isFlightPage(config, absolutePagePath)
+  await Promise.all(
+    Object.keys(pages).map(async (page) => {
+      const absolutePagePath = pages[page]
+      const bundleFile = normalizePagePath(page)
+      const isApiRoute = page.match(API_ROUTE)
+
+      const clientBundlePath = posix.join('pages', bundleFile)
+      const serverBundlePath = posix.join('pages', bundleFile)
+
+      const isLikeServerless = isTargetLikeServerless(target)
+      const isReserved = isReservedPage(page)
+      const isCustomError = isCustomErrorPage(page)
+      const isFlight = isFlightPage(config, absolutePagePath)
+      const isEdgeRuntime =
+        (await getPageRuntime(
+          join(pagesDir, absolutePagePath.slice(PAGES_DIR_ALIAS.length + 1)),
+          globalRuntime
+        )) === 'edge'
+
+      if (page.match(MIDDLEWARE_ROUTE)) {
+        const loaderOpts: MiddlewareLoaderOptions = {
+          absolutePagePath: pages[page],
+          page,
+        }
 
-    if (page.match(MIDDLEWARE_ROUTE)) {
-      const loaderOpts: MiddlewareLoaderOptions = {
-        absolutePagePath: pages[page],
-        page,
+        client[clientBundlePath] = `next-middleware-loader?${stringify(
+          loaderOpts
+        )}!`
+        return
       }
 
-      client[clientBundlePath] = `next-middleware-loader?${stringify(
-        loaderOpts
-      )}!`
-      return
-    }
+      if (isEdgeRuntime && !isReserved && !isCustomError && !isApiRoute) {
+        ssrEntries.set(clientBundlePath, { requireFlightManifest: isFlight })
+        edgeServer[serverBundlePath] = finalizeEntrypoint({
+          name: '[name].js',
+          value: `next-middleware-ssr-loader?${stringify({
+            dev: false,
+            page,
+            stringifiedConfig: JSON.stringify(config),
+            absolute500Path: pages['/500'] || '',
+            absolutePagePath,
+            isServerComponent: isFlight,
+            ...defaultServerlessOptions,
+          } as any)}!`,
+          isServer: false,
+          isEdgeServer: true,
+        })
+      }
 
-    if (edgeRuntime && !isReserved && !isCustomError && !isApiRoute) {
-      ssrEntries.set(clientBundlePath, { requireFlightManifest: isFlight })
-      edgeServer[serverBundlePath] = finalizeEntrypoint({
-        name: '[name].js',
-        value: `next-middleware-ssr-loader?${stringify({
-          dev: false,
+      if (isApiRoute && isLikeServerless) {
+        const serverlessLoaderOptions: ServerlessLoaderQuery = {
           page,
-          stringifiedConfig: JSON.stringify(config),
-          absolute500Path: pages['/500'] || '',
           absolutePagePath,
-          isServerComponent: isFlight,
           ...defaultServerlessOptions,
-        } as any)}!`,
-        isServer: false,
-        isEdgeServer: true,
-      })
-    }
-
-    if (isApiRoute && isLikeServerless) {
-      const serverlessLoaderOptions: ServerlessLoaderQuery = {
-        page,
-        absolutePagePath,
-        ...defaultServerlessOptions,
-      }
-      server[serverBundlePath] = `next-serverless-loader?${stringify(
-        serverlessLoaderOptions
-      )}!`
-    } else if (isApiRoute || target === 'server') {
-      if (!edgeRuntime || isReserved || isCustomError) {
-        server[serverBundlePath] = [absolutePagePath]
-      }
-    } else if (
-      isLikeServerless &&
-      page !== '/_app' &&
-      page !== '/_document' &&
-      !edgeRuntime
-    ) {
-      const serverlessLoaderOptions: ServerlessLoaderQuery = {
-        page,
-        absolutePagePath,
-        ...defaultServerlessOptions,
+        }
+        server[serverBundlePath] = `next-serverless-loader?${stringify(
+          serverlessLoaderOptions
+        )}!`
+      } else if (isApiRoute || target === 'server') {
+        if (!isEdgeRuntime || isReserved || isCustomError) {
+          server[serverBundlePath] = [absolutePagePath]
+        }
+      } else if (
+        isLikeServerless &&
+        page !== '/_app' &&
+        page !== '/_document' &&
+        !isEdgeRuntime
+      ) {
+        const serverlessLoaderOptions: ServerlessLoaderQuery = {
+          page,
+          absolutePagePath,
+          ...defaultServerlessOptions,
+        }
+        server[serverBundlePath] = `next-serverless-loader?${stringify(
+          serverlessLoaderOptions
+        )}!`
       }
-      server[serverBundlePath] = `next-serverless-loader?${stringify(
-        serverlessLoaderOptions
-      )}!`
-    }
 
-    if (page === '/_document') {
-      return
-    }
+      if (page === '/_document') {
+        return
+      }
 
-    if (!isApiRoute) {
-      const pageLoaderOpts: ClientPagesLoaderOptions = {
-        page,
-        absolutePagePath,
+      if (!isApiRoute) {
+        const pageLoaderOpts: ClientPagesLoaderOptions = {
+          page,
+          absolutePagePath,
+        }
+        const pageLoader = `next-client-pages-loader?${stringify(
+          pageLoaderOpts
+        )}!`
+
+        // Make sure next/router is a dependency of _app or else chunk splitting
+        // might cause the router to not be able to load causing hydration
+        // to fail
+
+        client[clientBundlePath] =
+          page === '/_app'
+            ? [pageLoader, require.resolve('../client/router')]
+            : pageLoader
       }
-      const pageLoader = `next-client-pages-loader?${stringify(
-        pageLoaderOpts
-      )}!`
-
-      // Make sure next/router is a dependency of _app or else chunk splitting
-      // might cause the router to not be able to load causing hydration
-      // to fail
-
-      client[clientBundlePath] =
-        page === '/_app'
-          ? [pageLoader, require.resolve('../client/router')]
-          : pageLoader
-    }
-  })
+    })
+  )
 
   return {
     client,