Update check for fallback pages during export (#33323)

This fixes our check for fallback pages during `next export` as we are currently erroring even when the erroneous pages are not included in the `exportPathMap`. This also adds additional tests to certify the expected behavior for the error. 

## Bug

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

Fixes: #29135

packages/next/export/index.ts

@@ -448,14 +448,12 @@ export default async function exportApp(
     if (prerenderManifest && !options.buildExport) {
       const fallbackEnabledPages = new Set()
 
-      for (const key of Object.keys(prerenderManifest.dynamicRoutes)) {
-        // only error if page is included in path map
-        if (!exportPathMap[key] && !excludedPrerenderRoutes.has(key)) {
-          continue
-        }
+      for (const path of Object.keys(exportPathMap)) {
+        const page = exportPathMap[path].page
+        const prerenderInfo = prerenderManifest.dynamicRoutes[page]
 
-        if (prerenderManifest.dynamicRoutes[key].fallback !== false) {
-          fallbackEnabledPages.add(key)
+        if (prerenderInfo && prerenderInfo.fallback !== false) {
+          fallbackEnabledPages.add(page)
         }
       }
 

test/integration/export-fallback-true-error/next.config.js

@@ -0,0 +1,7 @@
+module.exports = {
+  exportPathMap() {
+    return {
+      '/first': { page: '/[slug]' },
+    }
+  },
+}

test/lib/next-modes/base.ts

@@ -148,6 +148,9 @@ export class NextInstance {
     }
   }
 
+  public async export(): Promise<{ exitCode?: number; cliOutput?: string }> {
+    return {}
+  }
   public async setup(): Promise<void> {}
   public async start(): Promise<void> {}
   public async stop(): Promise<void> {

test/lib/next-modes/next-start.ts

@@ -6,6 +6,7 @@ import { spawn, SpawnOptions } from 'child_process'
 export class NextStartInstance extends NextInstance {
   private _buildId: string
   private _cliOutput: string
+  private spawnOpts: SpawnOptions
 
   public get buildId() {
     return this._buildId
@@ -19,11 +20,26 @@ export class NextStartInstance extends NextInstance {
     await super.createTestDir()
   }
 
+  private handleStdio = (childProcess) => {
+    childProcess.stdout.on('data', (chunk) => {
+      const msg = chunk.toString()
+      process.stdout.write(chunk)
+      this._cliOutput += msg
+      this.emit('stdout', [msg])
+    })
+    childProcess.stderr.on('data', (chunk) => {
+      const msg = chunk.toString()
+      process.stderr.write(chunk)
+      this._cliOutput += msg
+      this.emit('stderr', [msg])
+    })
+  }
+
   public async start() {
     if (this.childProcess) {
       throw new Error('next already started')
     }
-    const spawnOpts: SpawnOptions = {
+    this.spawnOpts = {
       cwd: this.testDir,
       stdio: ['ignore', 'pipe', 'pipe'],
       shell: false,
@@ -34,20 +50,6 @@ export class NextStartInstance extends NextInstance {
         __NEXT_RAND_PORT: '1',
       },
     }
-    const handleStdio = () => {
-      this.childProcess.stdout.on('data', (chunk) => {
-        const msg = chunk.toString()
-        process.stdout.write(chunk)
-        this._cliOutput += msg
-        this.emit('stdout', [msg])
-      })
-      this.childProcess.stderr.on('data', (chunk) => {
-        const msg = chunk.toString()
-        process.stderr.write(chunk)
-        this._cliOutput += msg
-        this.emit('stderr', [msg])
-      })
-    }
     let buildArgs = ['yarn', 'next', 'build']
     let startArgs = ['yarn', 'next', 'start']
 
@@ -60,8 +62,12 @@ export class NextStartInstance extends NextInstance {
 
     await new Promise<void>((resolve, reject) => {
       console.log('running', buildArgs.join(' '))
-      this.childProcess = spawn(buildArgs[0], buildArgs.slice(1), spawnOpts)
-      handleStdio()
+      this.childProcess = spawn(
+        buildArgs[0],
+        buildArgs.slice(1),
+        this.spawnOpts
+      )
+      this.handleStdio(this.childProcess)
       this.childProcess.on('exit', (code, signal) => {
         if (code || signal)
           reject(
@@ -85,8 +91,12 @@ export class NextStartInstance extends NextInstance {
     console.log('running', startArgs.join(' '))
 
     await new Promise<void>((resolve) => {
-      this.childProcess = spawn(startArgs[0], startArgs.slice(1), spawnOpts)
-      handleStdio()
+      this.childProcess = spawn(
+        startArgs[0],
+        startArgs.slice(1),
+        this.spawnOpts
+      )
+      this.handleStdio(this.childProcess)
 
       this.childProcess.on('close', (code, signal) => {
         if (this.isStopping) return
@@ -108,4 +118,33 @@ export class NextStartInstance extends NextInstance {
       this.on('stdout', readyCb)
     })
   }
+
+  public async export() {
+    return new Promise((resolve) => {
+      const curOutput = this._cliOutput.length
+      const exportArgs = ['yarn', 'next', 'export']
+
+      if (this.childProcess) {
+        throw new Error(
+          `can not run export while server is running, use next.stop() first`
+        )
+      }
+      console.log('running', exportArgs.join(' '))
+
+      this.childProcess = spawn(
+        exportArgs[0],
+        exportArgs.slice(1),
+        this.spawnOpts
+      )
+      this.handleStdio(this.childProcess)
+
+      this.childProcess.on('exit', (code, signal) => {
+        this.childProcess = undefined
+        resolve({
+          exitCode: signal || code,
+          cliOutput: this.cliOutput.substr(curOutput),
+        })
+      })
+    })
+  }
 }

test/production/fallback-export-error/index.test.ts

@@ -0,0 +1,89 @@
+import { createNext, FileRef } from 'e2e-utils'
+import { NextInstance } from 'test/lib/next-modes/base'
+import { renderViaHTTP } from 'next-test-utils'
+import { join } from 'path'
+
+describe('fallback export error', () => {
+  let next: NextInstance
+
+  beforeAll(async () => {
+    next = await createNext({
+      files: {
+        pages: new FileRef(join(__dirname, 'pages')),
+      },
+    })
+  })
+  afterAll(() => next.destroy())
+
+  it('should have built', async () => {
+    const html = await renderViaHTTP(next.url, '/')
+    expect(html).toContain('index page')
+  })
+
+  it('should not error with default exportPathMap', async () => {
+    await next.stop()
+
+    const result = await next.export()
+    console.log(result.cliOutput)
+
+    expect(result.exitCode).toBe(0)
+    expect(result.cliOutput).not.toContain(
+      'Found pages with `fallback` enabled'
+    )
+  })
+
+  it('should not error with valid exportPathMap', async () => {
+    await next.stop()
+    await next.patchFile(
+      'next.config.js',
+      `
+      module.exports = {
+        exportPathMap() {
+          return {
+            '/': { page: '/' },
+          }
+        }
+      }
+    `
+    )
+
+    try {
+      const result = await next.export()
+      console.log(result.cliOutput)
+
+      expect(result.exitCode).toBe(0)
+      expect(result.cliOutput).not.toContain(
+        'Found pages with `fallback` enabled'
+      )
+    } finally {
+      await next.deleteFile('next.config.js')
+    }
+  })
+
+  it('should error with invalid exportPathMap', async () => {
+    await next.stop()
+    await next.patchFile(
+      'next.config.js',
+      `
+      module.exports = {
+        exportPathMap() {
+          return {
+            '/': { page: '/' },
+            '/second': { page: '/[...slug]' }
+          }
+        }
+      }
+    `
+    )
+
+    try {
+      const result = await next.export()
+      console.log(result.cliOutput)
+
+      expect(result.exitCode).toBe(1)
+      expect(result.cliOutput).toContain('Found pages with `fallback` enabled')
+    } finally {
+      await next.deleteFile('next.config.js')
+    }
+  })
+})

test/production/fallback-export-error/pages/[...slug].js

@@ -0,0 +1,18 @@
+export function getStaticProps() {
+  return {
+    props: {
+      now: Date.now(),
+    },
+  }
+}
+
+export function getStaticPaths() {
+  return {
+    paths: ['/first'],
+    fallback: 'blocking',
+  }
+}
+
+export default function Page() {
+  return <p>catch-all page</p>
+}

test/production/fallback-export-error/pages/index.js

@@ -0,0 +1,3 @@
+export default function Page() {
+  return <p>index page</p>
+}