Fix validate use server in pages router

packages/next/src/build/analysis/get-page-static-info.test.ts

@@ -1,4 +1,10 @@
-import { getMiddlewareMatchers } from './get-page-static-info'
+import {
+  getMiddlewareMatchers,
+  getPagesPageStaticInfo,
+} from './get-page-static-info'
+import { join } from 'path'
+import { writeFile, mkdir, rm } from 'fs/promises'
+import { tmpdir } from 'os'
 
 describe('get-page-static-infos', () => {
   describe('getMiddlewareMatchers', () => {
@@ -42,4 +48,167 @@ describe('get-page-static-infos', () => {
       expect(regex.test('/apple.json')).toBe(true)
     })
   })
+
+  describe('getPagesPageStaticInfo', () => {
+    let testDir: string
+
+    beforeEach(async () => {
+      // Create a unique temporary directory for each test
+      testDir = join(tmpdir(), `next-test-${Date.now()}-${Math.random()}`)
+      await mkdir(testDir, { recursive: true })
+    })
+
+    afterEach(async () => {
+      // Clean up test directory
+      try {
+        await rm(testDir, { recursive: true, force: true })
+      } catch (e) {
+        // Ignore cleanup errors
+      }
+    })
+
+    it('should throw error when "use server" directive is used in Pages Router', async () => {
+      const pageContent = `"use server"
+
+export default function Page() {
+  return <div>Hello</div>
+}`
+
+      const pageFilePath = join(testDir, 'page.tsx')
+      await writeFile(pageFilePath, pageContent)
+
+      await expect(
+        getPagesPageStaticInfo({
+          pageFilePath,
+          nextConfig: {} as any,
+          isDev: false,
+          page: '/test-page',
+          pageType: 'pages' as const,
+        })
+      ).rejects.toThrow(
+        'Page "/test-page" cannot use "use server" directive. Server Actions are only supported in the App Router'
+      )
+    })
+
+    it('should throw error for "use server" even without other keywords (PARSE_PATTERN test)', async () => {
+      // This test verifies that PARSE_PATTERN includes "use\s" to trigger parsing
+      // Without this, files with only "use server" would skip AST parsing
+      const pageContent = `"use server"
+
+export default function Page() {
+  return <div>Hello</div>
+}`
+
+      const pageFilePath = join(testDir, 'page-minimal.tsx')
+      await writeFile(pageFilePath, pageContent)
+
+      // Should throw even though file has no getStaticProps, export const, etc.
+      await expect(
+        getPagesPageStaticInfo({
+          pageFilePath,
+          nextConfig: {} as any,
+          isDev: false,
+          page: '/minimal-page',
+          pageType: 'pages' as const,
+        })
+      ).rejects.toThrow(
+        'Page "/minimal-page" cannot use "use server" directive. Server Actions are only supported in the App Router'
+      )
+    })
+
+    it('should allow "use client" directive in Pages Router', async () => {
+      const pageContent = `"use client"
+
+export default function Page() {
+  return <div>Hello</div>
+}`
+
+      const pageFilePath = join(testDir, 'page.tsx')
+      await writeFile(pageFilePath, pageContent)
+
+      // Should not throw - "use client" is allowed in Pages Router
+      const result = await getPagesPageStaticInfo({
+        pageFilePath,
+        nextConfig: {} as any,
+        isDev: false,
+        page: '/test-page',
+        pageType: 'pages' as const,
+      })
+
+      expect(result).toBeDefined()
+      expect(result.type).toBe('pages')
+    })
+
+    it('should not throw error for Pages Router pages without directives', async () => {
+      const pageContent = `export default function Page() {
+  return <div>Hello</div>
+}
+
+export async function getStaticProps() {
+  return { props: {} }
+}`
+
+      const pageFilePath = join(testDir, 'page.tsx')
+      await writeFile(pageFilePath, pageContent)
+
+      const result = await getPagesPageStaticInfo({
+        pageFilePath,
+        nextConfig: {} as any,
+        isDev: false,
+        page: '/test-page',
+        pageType: 'pages' as const,
+      })
+
+      expect(result).toBeDefined()
+      expect(result.type).toBe('pages')
+      expect(result.getStaticProps).toBe(true)
+    })
+
+    it('should not throw error for directives in comments or strings', async () => {
+      const pageContent = `// "use server" in a comment
+export default function Page() {
+  const str = "use client"
+  return <div>Hello</div>
+}`
+
+      const pageFilePath = join(testDir, 'page.tsx')
+      await writeFile(pageFilePath, pageContent)
+
+      const result = await getPagesPageStaticInfo({
+        pageFilePath,
+        nextConfig: {} as any,
+        isDev: false,
+        page: '/test-page',
+        pageType: 'pages' as const,
+      })
+
+      expect(result).toBeDefined()
+      expect(result.type).toBe('pages')
+    })
+
+    it('should not trigger on React hooks or variables containing "use"', async () => {
+      const pageContent = `import { useState, useEffect } from 'react'
+
+export default function Page() {
+  const [state, setState] = useState(0)
+  const useServer = () => {}
+  useEffect(() => {}, [])
+  return <div>Hello</div>
+}`
+
+      const pageFilePath = join(testDir, 'page.tsx')
+      await writeFile(pageFilePath, pageContent)
+
+      const result = await getPagesPageStaticInfo({
+        pageFilePath,
+        nextConfig: {} as any,
+        isDev: false,
+        page: '/test-page',
+        pageType: 'pages' as const,
+      })
+
+      expect(result).toBeDefined()
+      expect(result.type).toBe('pages')
+    })
+  })
 })

packages/next/src/build/analysis/get-page-static-info.ts

@@ -42,8 +42,12 @@ import { normalizeAppPath } from '../../shared/lib/router/utils/app-paths'
 import { normalizePagePath } from '../../shared/lib/page-path/normalize-page-path'
 import { isProxyFile } from '../utils'
 
+// Pattern to detect if a file needs AST parsing for static analysis.
+// Includes 'use\s' to catch "use server" and "use client" directives.
+// The \s (whitespace) requirement prevents false matches on variable names
+// like useState, useEffect, or useServer.
 const PARSE_PATTERN =
-  /(?<!(_jsx|jsx-))runtime|preferredRegion|getStaticProps|getServerSideProps|generateStaticParams|export const|generateImageMetadata|generateSitemaps|middleware|proxy/
+  /(?<!(_jsx|jsx-))runtime|preferredRegion|getStaticProps|getServerSideProps|generateStaticParams|export const|generateImageMetadata|generateSitemaps|middleware|proxy|use\s/
 
 export type ProxyMatcher = {
   regexp: string
@@ -733,14 +737,24 @@ export async function getPagesPageStaticInfo({
     isDev,
   })
 
-  const { getServerSideProps, getStaticProps, exports } = checkExports(
-    ast,
-    PagesSegmentConfigSchemaKeys,
-    page
-  )
+  const { getServerSideProps, getStaticProps, exports, directives } =
+    checkExports(ast, PagesSegmentConfigSchemaKeys, page)
 
   const { type: rsc } = getRSCModuleInformation(content, true)
 
+  // Validate that use server directive is not used in Pages Router.
+  // Server Actions are only supported in the App Router.
+  //
+  // Note: This validation only checks the page file itself, not nested components
+  // that are imported. For comprehensive server-only validation in nested components,
+  // use `import 'server-only'` which is validated during the build process regardless
+  // of whether the code is in a page file or a nested component.
+  if (directives?.has('server')) {
+    throw new Error(
+      `Page "${page}" cannot use "use server" directive. Server Actions are only supported in the App Router. To use Server Actions, migrate to the App Router: https://nextjs.org/docs/app/building-your-application/upgrading/app-router-migration`
+    )
+  }
+
   const exportedConfig: Record<string, unknown> = {}
   if (exports) {
     for (const property of exports) {

test/development/acceptance/use-directives-in-pages-router.test.ts

@@ -0,0 +1,84 @@
+/* eslint-env jest */
+import { nextTestSetup } from 'e2e-utils'
+import { createSandbox } from 'development-sandbox'
+import { outdent } from 'outdent'
+
+const initialFiles = new Map([
+  ['app/_.js', ''], // app dir need to exists, otherwise the SWC RSC checks will not run
+  [
+    'pages/index.js',
+    outdent`
+      export default function Page() { 
+        return <div>Hello</div> 
+      }
+    `,
+  ],
+])
+
+describe('Error for "use server" directive in Pages Router', () => {
+  const { next } = nextTestSetup({
+    files: {},
+    skipStart: true,
+  })
+
+  test('"use server" directive is not allowed in Pages Router', async () => {
+    await using sandbox = await createSandbox(
+      next,
+      new Map([
+        ...initialFiles,
+        [
+          'pages/test-page.js',
+          outdent`
+            "use server"
+
+            export default function Page() {
+              return <div>Hello</div>
+            }
+          `,
+        ],
+      ])
+    )
+    const { session } = sandbox
+
+    await session.assertHasRedbox()
+    await expect(session.getRedboxSource()).resolves.toMatch(
+      /cannot use "use server" directive.*Server Actions are only supported in the App Router/
+    )
+  })
+
+  test('"use client" directive is allowed in Pages Router', async () => {
+    await using sandbox = await createSandbox(
+      next,
+      new Map([
+        ...initialFiles,
+        [
+          'pages/test-page.js',
+          outdent`
+            "use client"
+
+            export default function Page() {
+              return <div>Hello</div>
+            }
+          `,
+        ],
+      ])
+    )
+    const { session, browser } = sandbox
+
+    // Should not have a redbox - "use client" is allowed
+    await session.assertNoRedbox()
+
+    const text = await browser.elementByCss('body').text()
+    expect(text).toContain('Hello')
+  })
+
+  test('Pages Router pages without directives work correctly', async () => {
+    await using sandbox = await createSandbox(next, initialFiles)
+    const { session, browser } = sandbox
+
+    await session.assertNoRedbox()
+
+    const text = await browser.elementByCss('body').text()
+    expect(text).toContain('Hello')
+  })
+})