fix(next): do not generate conflicting lambdas when using basePath wi…

…th app router (#10738) When using `basePath` with statically generated routes, the builder currently generates lambdas for the root route that conflict with the prerender functions generated. E.g. if we have `basePath: "test"` and a root route at: `app/page.js`, this is currently the output: ``` test test.rsc test/index test/index.rsc ``` The result is that visiting the deployed app at `/test` renders an incomplete page. On the other hand visiting `/test/index` outputs the expected markup. It seems like the intent is that we want to delete the lambdas that conflict with the prerender functions. I've updated the lambda name generation logic when doing the deleting to line up with how the lambda names are generated initially.
vercel · Nov 3, 2023 · 33cc8e0 · 33cc8e0
1 parent c0efce2
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diff --git a/.changeset/silver-rice-rescue.md b/.changeset/silver-rice-rescue.md
@@ -0,0 +1,5 @@
+---
+'@vercel/next': patch
+---
+
+Fixes a case where using `basePath` along with static generation would output a lambda that conflicts with the root route.
diff --git a/packages/next/src/server-build.ts b/packages/next/src/server-build.ts
@@ -1132,7 +1132,10 @@ export async function serverBuild({
       route = normalizeLocalePath(route, routesManifest.i18n.locales).pathname;
     }
     delete lambdas[
-      path.posix.join('.', entryDirectory, route === '/' ? 'index' : route)
+      normalizeIndexOutput(
+        path.posix.join('./', entryDirectory, route === '/' ? '/index' : route),
+        true
+      )
     ];
   });
 

diff --git a/packages/next/test/integration/app-router-basepath/app/layout.js b/packages/next/test/integration/app-router-basepath/app/layout.js
@@ -0,0 +1,9 @@
+const Layout = ({ children }) => {
+  return (
+    <html>
+      <body>{children}</body>
+    </html>
+  );
+};
+
+export default Layout;
diff --git a/packages/next/test/integration/app-router-basepath/app/page.js b/packages/next/test/integration/app-router-basepath/app/page.js
@@ -0,0 +1,5 @@
+const Home = () => {
+  return <div>Home</div>;
+};
+
+export default Home;
diff --git a/packages/next/test/integration/app-router-basepath/next.config.js b/packages/next/test/integration/app-router-basepath/next.config.js
@@ -0,0 +1,7 @@
+/** @type {import('next').NextConfig} */
+const nextConfig = {
+  reactStrictMode: true,
+  basePath: '/test',
+};
+
+module.exports = nextConfig;
diff --git a/packages/next/test/integration/app-router-basepath/package.json b/packages/next/test/integration/app-router-basepath/package.json
@@ -0,0 +1,8 @@
+{
+  "dependencies": {
+    "next": "canary",
+    "react": "latest",
+    "react-dom": "latest"
+  },
+  "ignoreNextjsUpdates": true
+}
diff --git a/packages/next/test/integration/app-router-basepath/vercel.json b/packages/next/test/integration/app-router-basepath/vercel.json
@@ -0,0 +1,4 @@
+{
+  "version": 2,
+  "builds": [{ "src": "package.json", "use": "@vercel/next" }]
+}
diff --git a/packages/next/test/integration/integration-2.test.js b/packages/next/test/integration/integration-2.test.js
@@ -441,3 +441,26 @@ it('should handle edge functions in app with basePath', async () => {
   expect(lambdas.size).toBe(1);
   expect(edgeFunctions.size).toBe(4);
 });
+
+it('should not generate lambdas that conflict with static index route in app with basePath', async () => {
+  const {
+    buildResult: { output },
+  } = await runBuildLambda(path.join(__dirname, 'app-router-basepath'));
+
+  expect(output['test']).not.toBeDefined();
+  expect(output['test.rsc']).not.toBeDefined();
+  expect(output['test/index'].type).toBe('Prerender');
+  expect(output['test/index.rsc'].type).toBe('Prerender');
+
+  expect(output['test/_not-found']).toBeDefined();
+  expect(output['test/_not-found'].type).toBe('Lambda');
+
+  const lambdas = new Set();
+
+  for (const item of Object.values(output)) {
+    if (item.type === 'Lambda') {
+      lambdas.add(item);
+    }
+  }
+  expect(lambdas.size).toBe(1);
+});