error when output: export is used with intercepting routes (vercel#75058)

Intercepting routes are built on top of
[rewrites](https://nextjs.org/docs/app/api-reference/config/next-config-js/rewrites)
which is one of the listed [unsupported
features](https://nextjs.org/docs/app/building-your-application/deploying/static-exports#unsupported-features)
of `output: "export"`.

However, because the Next.js server injects the interception routes,
it's not caught by existing validation logic in the export flow.

This properly documents that intercepting routes are not currently
supported by `output: "export"` and hard errors in next dev/build if
detected. Previously route interception would just not have worked,
instead serving the non-intercepted page when built, leading to a
confusing experience.

We eventually want to support this with improved SPA/export features,
however that's out of scope for this PR: the goal here is to ensure
we're providing more immediate feedback about the fact that this is
unsupported.

Author: ztanner

docs/01-app/03-building-your-application/10-deploying/02-static-exports.mdx

@@ -288,6 +288,7 @@ Features that require a Node.js server, or dynamic logic that cannot be computed
 - [Image Optimization](/docs/app/building-your-application/optimizing/images) with the default `loader`
 - [Draft Mode](/docs/app/building-your-application/configuring/draft-mode)
 - [Server Actions](/docs/app/building-your-application/data-fetching/server-actions-and-mutations)
+- [Intercepting Routes](/docs/app/building-your-application/routing/intercepting-routes)
 
 Attempting to use any of these features with `next dev` will result in an error, similar to setting the [`dynamic`](/docs/app/api-reference/file-conventions/route-segment-config#dynamic) option to `error` in the root layout.
 

packages/next/errors.json

@@ -622,5 +622,7 @@
   "621": "Required root params (%s) were not provided in generateStaticParams for %s, please provide at least one value for each.",
   "622": "A required root parameter (%s) was not provided in generateStaticParams for %s, please provide at least one value.",
   "623": "Invalid quality prop (%s) on \\`next/image\\` does not match \\`images.qualities\\` configured in your \\`next.config.js\\`\\nSee more info: https://nextjs.org/docs/messages/next-image-unconfigured-qualities",
-  "624": "Internal Next.js Error: createMutableActionQueue was called more than once"
+  "624": "Internal Next.js Error: createMutableActionQueue was called more than once",
+  "625": "Server Actions are not supported with static export.\\nRead more: https://nextjs.org/docs/app/building-your-application/deploying/static-exports#unsupported-features",
+  "626": "Intercepting routes are not supported with static export.\\nRead more: https://nextjs.org/docs/app/building-your-application/deploying/static-exports#unsupported-features"
 }

packages/next/src/export/index.ts

@@ -32,6 +32,7 @@ import {
   SERVER_DIRECTORY,
   SERVER_REFERENCE_MANIFEST,
   APP_PATH_ROUTES_MANIFEST,
+  ROUTES_MANIFEST,
 } from '../shared/lib/constants'
 import loadConfig from '../server/config'
 import type { ExportPathMap } from '../server/config-shared'
@@ -52,6 +53,7 @@ import { formatManifest } from '../build/manifests/formatter/format-manifest'
 import { TurborepoAccessTraceResult } from '../build/turborepo-access-trace'
 import { createProgress } from '../build/progress'
 import type { DeepReadonly } from '../shared/lib/deep-readonly'
+import { isInterceptionRouteRewrite } from '../lib/generate-interception-routes-rewrites'
 
 export class ExportError extends Error {
   code = 'NEXT_EXPORT_ERROR'
@@ -302,13 +304,29 @@ async function exportAppImpl(
     serverActionsManifest = require(
       join(distDir, SERVER_DIRECTORY, SERVER_REFERENCE_MANIFEST + '.json')
     )
+
     if (nextConfig.output === 'export') {
+      const routesManifest = require(join(distDir, ROUTES_MANIFEST))
+
+      // We already prevent rewrites earlier in the process, however Next.js will insert rewrites
+      // for interception routes so we need to check for that here.
+      if (routesManifest?.rewrites?.beforeFiles?.length > 0) {
+        const hasInterceptionRouteRewrite =
+          routesManifest.rewrites.beforeFiles.some(isInterceptionRouteRewrite)
+
+        if (hasInterceptionRouteRewrite) {
+          throw new ExportError(
+            `Intercepting routes are not supported with static export.\nRead more: https://nextjs.org/docs/app/building-your-application/deploying/static-exports#unsupported-features`
+          )
+        }
+      }
+
       if (
         Object.keys(serverActionsManifest.node).length > 0 ||
         Object.keys(serverActionsManifest.edge).length > 0
       ) {
         throw new ExportError(
-          `Server Actions are not supported with static export.`
+          `Server Actions are not supported with static export.\nRead more: https://nextjs.org/docs/app/building-your-application/deploying/static-exports#unsupported-features`
         )
       }
     }

packages/next/src/server/dev/next-dev-server.ts

@@ -604,6 +604,14 @@ export default class DevServer extends Server {
       this.nextConfig.basePath
     ).map((route) => new RegExp(buildCustomRoute('rewrite', route).regex))
 
+    if (this.nextConfig.output === 'export' && rewrites.length > 0) {
+      Log.error(
+        'Intercepting routes are not supported with static export.\nRead more: https://nextjs.org/docs/app/building-your-application/deploying/static-exports#unsupported-features'
+      )
+
+      process.exit(1)
+    }
+
     return rewrites ?? []
   }
 

test/e2e/app-dir/actions/app-action-export.test.ts

@@ -27,6 +27,8 @@ describe('app-dir action handling - next export', () => {
       }
       `
     )
+    // interception routes are also not supported with export
+    await next.remove('app/interception-routes')
     try {
       await next.start()
     } catch {}

test/e2e/app-dir/interception-routes-output-export/app/@modal/(.)page/page.tsx

@@ -0,0 +1,3 @@
+export default function Page() {
+  return 'intercepted'
+}

test/e2e/app-dir/interception-routes-output-export/app/@modal/default.tsx

@@ -0,0 +1 @@
+export default () => null

test/e2e/app-dir/interception-routes-output-export/app/default.tsx

@@ -0,0 +1,3 @@
+export default function Default() {
+  return null
+}

test/e2e/app-dir/interception-routes-output-export/app/layout.tsx

@@ -0,0 +1,13 @@
+export default function Layout(props: {
+  children: React.ReactNode
+  modal: React.ReactNode
+}) {
+  return (
+    <html>
+      <body>
+        <div id="children">{props.children}</div>
+        <div id="modal">{props.modal}</div>
+      </body>
+    </html>
+  )
+}

test/e2e/app-dir/interception-routes-output-export/app/page.tsx

@@ -0,0 +1,9 @@
+import Link from 'next/link'
+
+export default function Page() {
+  return (
+    <div>
+      <Link href="/page">To /page</Link>
+    </div>
+  )
+}