fix(standalone): fixed output: "standalone" crashing build when the…

…re is no `app/` page (#51993)

### What?
This PR fixes build crashing when `output: 'standalone'` and `experimental.appDir` is enabled but there is no app pages.

### How?
It does that by checking whether `.next/server/app` exists before copying the folder to `.next/standalone/...`

Closes #51828
Fixes #44442
Fixes #44120

packages/next/src/build/index.ts

@@ -11,7 +11,7 @@ import { loadEnvConfig } from '@next/env'
 import chalk from 'next/dist/compiled/chalk'
 import crypto from 'crypto'
 import { isMatch, makeRe } from 'next/dist/compiled/micromatch'
-import { promises } from 'fs'
+import { promises as fs, existsSync as fsExistsSync } from 'fs'
 import os from 'os'
 import { Worker } from '../lib/worker'
 import { defaultConfig } from '../server/config-shared'
@@ -186,7 +186,7 @@ async function generateClientSsgManifest(
     ssgPages
   )};self.__SSG_MANIFEST_CB&&self.__SSG_MANIFEST_CB()`
 
-  await promises.writeFile(
+  await fs.writeFile(
     path.join(distDir, CLIENT_STATIC_FILES_PATH, buildId, '_ssgManifest.js'),
     clientSsgManifestContent
   )
@@ -257,10 +257,7 @@ export default async function build(
       let buildId: string = ''
 
       if (isGenerate) {
-        buildId = await promises.readFile(
-          path.join(distDir, 'BUILD_ID'),
-          'utf8'
-        )
+        buildId = await fs.readFile(path.join(distDir, 'BUILD_ID'), 'utf8')
       } else {
         buildId = await nextBuildSpan
           .traceChild('generate-buildid')
@@ -808,7 +805,7 @@ export default async function build(
         .traceChild('create-dist-dir')
         .traceAsyncFn(async () => {
           try {
-            await promises.mkdir(distDir, { recursive: true })
+            await fs.mkdir(distDir, { recursive: true })
             return true
           } catch (err) {
             if (isError(err) && err.code === 'EPERM') {
@@ -830,7 +827,7 @@ export default async function build(
 
       // Ensure commonjs handling is used for files in the distDir (generally .next)
       // Files outside of the distDir can be "type": "module"
-      await promises.writeFile(
+      await fs.writeFile(
         path.join(distDir, 'package.json'),
         '{"type": "commonjs"}'
       )
@@ -839,7 +836,7 @@ export default async function build(
       await nextBuildSpan
         .traceChild('write-routes-manifest')
         .traceAsyncFn(() =>
-          promises.writeFile(
+          fs.writeFile(
             routesManifestPath,
             JSON.stringify(routesManifest),
             'utf8'
@@ -917,7 +914,6 @@ export default async function build(
               ? path.join(SERVER_DIRECTORY, FONT_MANIFEST)
               : null,
             BUILD_ID_FILE,
-            appDir ? path.join(SERVER_DIRECTORY, APP_PATHS_MANIFEST) : null,
             path.join(SERVER_DIRECTORY, NEXT_FONT_MANIFEST + '.js'),
             path.join(SERVER_DIRECTORY, NEXT_FONT_MANIFEST + '.json'),
             ...(hasInstrumentationHook
@@ -1052,7 +1048,7 @@ export default async function build(
               })
               await binding.turbo.startTrace(action, turboTasksForTrace)
               if (turbotraceOutputPath && turbotraceFiles) {
-                const existedNftFile = await promises
+                const existedNftFile = await fs
                   .readFile(turbotraceOutputPath, 'utf8')
                   .then((existedContent) => JSON.parse(existedContent))
                   .catch(() => ({
@@ -1062,7 +1058,7 @@ export default async function build(
                 existedNftFile.files.push(...turbotraceFiles)
                 const filesSet = new Set(existedNftFile.files)
                 existedNftFile.files = [...filesSet]
-                await promises.writeFile(
+                await fs.writeFile(
                   turbotraceOutputPath,
                   JSON.stringify(existedNftFile),
                   'utf8'
@@ -1105,14 +1101,14 @@ export default async function build(
       const appDefaultConfigs = new Map<string, AppConfig>()
       const pageInfos = new Map<string, PageInfo>()
       const pagesManifest = JSON.parse(
-        await promises.readFile(manifestPath, 'utf8')
+        await fs.readFile(manifestPath, 'utf8')
       ) as PagesManifest
       const buildManifest = JSON.parse(
-        await promises.readFile(buildManifestPath, 'utf8')
+        await fs.readFile(buildManifestPath, 'utf8')
       ) as BuildManifest
       const appBuildManifest = appDir
         ? (JSON.parse(
-            await promises.readFile(appBuildManifestPath, 'utf8')
+            await fs.readFile(appBuildManifestPath, 'utf8')
           ) as AppBuildManifest)
         : undefined
 
@@ -1127,7 +1123,7 @@ export default async function build(
 
       if (appDir) {
         appPathsManifest = JSON.parse(
-          await promises.readFile(
+          await fs.readFile(
             path.join(distDir, SERVER_DIRECTORY, APP_PATHS_MANIFEST),
             'utf8'
           )
@@ -1136,7 +1132,7 @@ export default async function build(
         Object.keys(appPathsManifest).forEach((entry) => {
           appPathRoutes[entry] = normalizeAppPath(entry)
         })
-        await promises.writeFile(
+        await fs.writeFile(
           path.join(distDir, APP_PATH_ROUTES_MANIFEST),
           JSON.stringify(appPathRoutes, null, 2)
         )
@@ -1739,7 +1735,7 @@ export default async function build(
       }
 
       if (Object.keys(functionsConfigManifest).length > 0) {
-        await promises.writeFile(
+        await fs.writeFile(
           path.join(distDir, SERVER_DIRECTORY, FUNCTIONS_CONFIG_MANIFEST),
           JSON.stringify(functionsConfigManifest, null, 2)
         )
@@ -1833,7 +1829,7 @@ export default async function build(
               )
               const pageDir = path.dirname(traceFile)
               const traceContent = JSON.parse(
-                await promises.readFile(traceFile, 'utf8')
+                await fs.readFile(traceFile, 'utf8')
               )
               const includes: string[] = []
 
@@ -1866,7 +1862,7 @@ export default async function build(
                 })
               }
 
-              await promises.writeFile(
+              await fs.writeFile(
                 traceFile,
                 JSON.stringify({
                   version: traceContent.version,
@@ -1913,21 +1909,18 @@ export default async function build(
 
               await Promise.all(
                 lockFiles.map(async (lockFile) => {
-                  cacheHash.update(await promises.readFile(lockFile))
+                  cacheHash.update(await fs.readFile(lockFile))
                 })
               )
               cacheKey = cacheHash.digest('hex')
 
               try {
                 const existingTrace = JSON.parse(
-                  await promises.readFile(cachedTracePath, 'utf8')
+                  await fs.readFile(cachedTracePath, 'utf8')
                 )
 
                 if (existingTrace.cacheKey === cacheKey) {
-                  await promises.copyFile(
-                    cachedTracePath,
-                    nextServerTraceOutput
-                  )
+                  await fs.copyFile(cachedTracePath, nextServerTraceOutput)
                   return
                 }
               } catch (_) {}
@@ -2060,7 +2053,7 @@ export default async function build(
                 addToTracedFiles(root, file)
               })
             }
-            await promises.writeFile(
+            await fs.writeFile(
               nextServerTraceOutput,
               JSON.stringify({
                 version: 1,
@@ -2071,8 +2064,8 @@ export default async function build(
                 files: string[]
               })
             )
-            await promises.unlink(cachedTracePath).catch(() => {})
-            await promises
+            await fs.unlink(cachedTracePath).catch(() => {})
+            await fs
               .copyFile(nextServerTraceOutput, cachedTracePath)
               .catch(() => {})
           })
@@ -2130,7 +2123,7 @@ export default async function build(
           }
         })
 
-        await promises.writeFile(
+        await fs.writeFile(
           routesManifestPath,
           JSON.stringify(routesManifest),
           'utf8'
@@ -2206,14 +2199,14 @@ export default async function build(
         })
       )
 
-      await promises.writeFile(
+      await fs.writeFile(
         path.join(distDir, SERVER_FILES_MANIFEST),
         JSON.stringify(requiredServerFiles),
         'utf8'
       )
 
       const middlewareManifest: MiddlewareManifest = JSON.parse(
-        await promises.readFile(
+        await fs.readFile(
           path.join(distDir, SERVER_DIRECTORY, MIDDLEWARE_MANIFEST),
           'utf8'
         )
@@ -2440,7 +2433,7 @@ export default async function build(
           // remove server bundles that were exported
           for (const page of staticPages) {
             const serverBundle = getPagePath(page, distDir, undefined, false)
-            await promises.unlink(serverBundle)
+            await fs.unlink(serverBundle)
           }
 
           for (const [originalAppPath, routes] of appStaticPaths) {
@@ -2623,8 +2616,8 @@ export default async function build(
                 // output with the locale prefixed so don't attempt moving
                 // without the prefix
                 if ((!i18n || additionalSsgFile) && !isNotFound) {
-                  await promises.mkdir(path.dirname(dest), { recursive: true })
-                  await promises.rename(orig, dest)
+                  await fs.mkdir(path.dirname(dest), { recursive: true })
+                  await fs.rename(orig, dest)
                 } else if (i18n && !isSsg) {
                   // this will be updated with the locale prefixed variant
                   // since all files are output with the locale prefix
@@ -2669,10 +2662,10 @@ export default async function build(
                     if (!isSsg) {
                       pagesManifest[curPath] = updatedRelativeDest
                     }
-                    await promises.mkdir(path.dirname(updatedDest), {
+                    await fs.mkdir(path.dirname(updatedDest), {
                       recursive: true,
                     })
-                    await promises.rename(updatedOrig, updatedDest)
+                    await fs.rename(updatedOrig, updatedDest)
                   }
                 }
               })
@@ -2693,7 +2686,7 @@ export default async function build(
                   .replace(/\\/g, '/')
 
                 if (await fileExists(orig)) {
-                  await promises.copyFile(
+                  await fs.copyFile(
                     orig,
                     path.join(distDir, 'server', updatedRelativeDest)
                   )
@@ -2861,8 +2854,8 @@ export default async function build(
 
           // remove temporary export folder
           await recursiveDelete(exportOptions.outdir)
-          await promises.rmdir(exportOptions.outdir)
-          await promises.writeFile(
+          await fs.rmdir(exportOptions.outdir)
+          await fs.writeFile(
             manifestPath,
             JSON.stringify(pagesManifest, null, 2),
             'utf8'
@@ -2954,12 +2947,12 @@ export default async function build(
         NextBuildContext.allowedRevalidateHeaderKeys =
           config.experimental.allowedRevalidateHeaderKeys
 
-        await promises.writeFile(
+        await fs.writeFile(
           path.join(distDir, PRERENDER_MANIFEST),
           JSON.stringify(prerenderManifest),
           'utf8'
         )
-        await promises.writeFile(
+        await fs.writeFile(
           path.join(distDir, PRERENDER_MANIFEST).replace(/\.json$/, '.js'),
           `self.__PRERENDER_MANIFEST=${JSON.stringify(
             JSON.stringify(prerenderManifest)
@@ -2979,12 +2972,12 @@ export default async function build(
           preview: previewProps,
           notFoundRoutes: [],
         }
-        await promises.writeFile(
+        await fs.writeFile(
           path.join(distDir, PRERENDER_MANIFEST),
           JSON.stringify(prerenderManifest),
           'utf8'
         )
-        await promises.writeFile(
+        await fs.writeFile(
           path.join(distDir, PRERENDER_MANIFEST).replace(/\.json$/, '.js'),
           `self.__PRERENDER_MANIFEST=${JSON.stringify(
             JSON.stringify(prerenderManifest)
@@ -3006,15 +2999,15 @@ export default async function build(
         pathname: makeRe(p.pathname ?? '**').source,
       }))
 
-      await promises.writeFile(
+      await fs.writeFile(
         path.join(distDir, IMAGES_MANIFEST),
         JSON.stringify({
           version: 1,
           images,
         }),
         'utf8'
       )
-      await promises.writeFile(
+      await fs.writeFile(
         path.join(distDir, EXPORT_MARKER),
         JSON.stringify({
           version: 1,
@@ -3024,7 +3017,7 @@ export default async function build(
         }),
         'utf8'
       )
-      await promises.unlink(path.join(distDir, EXPORT_DETAIL)).catch((err) => {
+      await fs.unlink(path.join(distDir, EXPORT_DETAIL)).catch((err) => {
         if (err.code === 'ENOENT') {
           return Promise.resolve()
         }
@@ -3048,10 +3041,10 @@ export default async function build(
             'standalone',
             path.relative(outputFileTracingRoot, filePath)
           )
-          await promises.mkdir(path.dirname(outputPath), {
+          await fs.mkdir(path.dirname(outputPath), {
             recursive: true,
           })
-          await promises.copyFile(filePath, outputPath)
+          await fs.copyFile(filePath, outputPath)
         }
         await recursiveCopy(
           path.join(distDir, SERVER_DIRECTORY, 'pages'),
@@ -3065,17 +3058,20 @@ export default async function build(
           { overwrite: true }
         )
         if (appDir) {
-          await recursiveCopy(
-            path.join(distDir, SERVER_DIRECTORY, 'app'),
-            path.join(
-              distDir,
-              'standalone',
-              path.relative(outputFileTracingRoot, distDir),
-              SERVER_DIRECTORY,
-              'app'
-            ),
-            { overwrite: true }
-          )
+          const originalServerApp = path.join(distDir, SERVER_DIRECTORY, 'app')
+          if (fsExistsSync(originalServerApp)) {
+            await recursiveCopy(
+              originalServerApp,
+              path.join(
+                distDir,
+                'standalone',
+                path.relative(outputFileTracingRoot, distDir),
+                SERVER_DIRECTORY,
+                'app'
+              ),
+              { overwrite: true }
+            )
+          }
         }
       }
 

test/production/standalone-mode/no-app-routes/app/layout.js

@@ -0,0 +1,8 @@
+export default function Root({ children }) {
+  return (
+    <html>
+      <head></head>
+      <body>{children}</body>
+    </html>
+  )
+}

test/production/standalone-mode/no-app-routes/index.test.ts

@@ -0,0 +1,14 @@
+import { createNextDescribe } from 'e2e-utils'
+
+createNextDescribe(
+  'standalone mode - no app routes',
+  {
+    files: __dirname,
+  },
+  ({ next }) => {
+    it('should handle pages rendering correctly', async () => {
+      const browser = await next.browser('/hello')
+      expect(await browser.elementByCss('#index').text()).toBe('index-page')
+    })
+  }
+)

test/production/standalone-mode/no-app-routes/next.config.js

@@ -0,0 +1,3 @@
+module.exports = {
+  output: 'standalone',
+}