Add warning for API export (#8250)

packages/next/export/index.js

@@ -19,6 +19,7 @@ import {
 import createProgress from 'tty-aware-progress'
 import { promisify } from 'util'
 import { recursiveDelete } from '../lib/recursive-delete'
+import { API_ROUTE } from '../lib/constants'
 import { formatAmpMessages } from '../build/output/index'
 
 const mkdirp = promisify(mkdirpModule)
@@ -35,6 +36,7 @@ export default async function (dir, options, configuration) {
   const threads = options.threads || Math.max(cpus().length - 1, 1)
   const distDir = join(dir, nextConfig.distDir)
   const subFolders = nextConfig.exportTrailingSlash
+  let apiPage = false
 
   if (!options.buildExport && nextConfig.target !== 'server') {
     throw new Error(
@@ -60,7 +62,20 @@ export default async function (dir, options, configuration) {
   for (const page of pages) {
     // _document and _app are not real pages
     // _error is exported as 404.html later on
-    if (page === '/_document' || page === '/_app' || page === '/_error') {
+    const isApiRoute = page.match(API_ROUTE)
+
+    // Warn about API pages export
+    if (isApiRoute && !apiPage) {
+      apiPage = true
+      log(`  API pages are not supported in export`)
+    }
+
+    if (
+      page === '/_document' ||
+      page === '/_app' ||
+      page === '/_error' ||
+      isApiRoute
+    ) {
       continue
     }
 

test/integration/api-support/test/index.test.js

@@ -10,6 +10,7 @@ import {
   renderViaHTTP,
   nextBuild,
   nextStart,
+  runNextCommand,
   File
 } from 'next-test-utils'
 import json from '../big.json'
@@ -285,6 +286,17 @@ function runTests (serverless = false) {
     }
   })
 
+  if (!serverless) {
+    it('should warn about API export', async () => {
+      const { stdout } = await runNextCommand(['export', appDir], {
+        stdout: true,
+        stderr: true
+      })
+
+      expect(stdout).toContain('API pages are not supported in export')
+    })
+  }
+
   it('should return data on dynamic optional nested route', async () => {
     const data = await fetchViaHTTP(
       appPort,