[next]: ensure user rewrites match to action outputs (#11628)

The builder normalizes user rewrites that target pages that have special outputs (`.rsc`, `.prefetch.rsc`). When we added support for `.action` outputs, we need to perform this same normalization to ensure that user rewrites still match. If the rewrite was a greedy match (eg `/:path*`) it'd be ok, but more specific rewrites would have the issue.

.changeset/smart-horses-rescue.md

@@ -0,0 +1,5 @@
+---
+'@vercel/next': patch
+---
+
+Ensure user rewrites still match to action outputs

packages/next/src/server-build.ts

@@ -252,9 +252,19 @@ export async function serverBuild({
 
     for (const rewrite of afterFilesRewrites) {
       if (rewrite.src && rewrite.dest) {
+        // ensures that userland rewrites are still correctly matched to their special outputs
+        // PPR should match .prefetch.rsc, .rsc, and .action
+        // non-PPR should match .rsc and .action
+        // we only add `.action` handling to the regex if flagged on in the build
+        const rscSuffix = isAppPPREnabled
+          ? `(\\.prefetch)?\\.rsc${hasActionOutputSupport ? '|\\.action' : ''}`
+          : hasActionOutputSupport
+          ? '(\\.action|\\.rsc)'
+          : '\\.rsc';
+
         rewrite.src = rewrite.src.replace(
           /\/?\(\?:\/\)\?/,
-          `(?<rscsuff>${isAppPPREnabled ? '(\\.prefetch)?' : ''}\\.rsc)?(?:/)?`
+          `(?<rscsuff>${rscSuffix})?(?:/)?`
         );
         let destQueryIndex = rewrite.dest.indexOf('?');
 

packages/next/test/fixtures/00-app-dir-actions-experimental-streaming/index.test.js

@@ -273,6 +273,26 @@ describe(`${__dirname.split(path.sep).pop()}`, () => {
       expect(body).toContain(JSON.stringify(['id', '1', 'd']));
       expect(body).not.toContain(JSON.stringify(['id', '1.action', 'd']));
     });
+
+    it('should work when a rewrite targets an action', async () => {
+      const targetPath = `${basePath}/rsc/static`;
+      const canonicalPath = `/rewrite/${basePath}/rsc/static`;
+      const actionId = findActionId(targetPath, runtime);
+
+      const res = await fetch(
+        `${ctx.deploymentUrl}${canonicalPath}`,
+        generateFormDataPayload(actionId)
+      );
+
+      expect(res.status).toEqual(200);
+      expect(res.headers.get('x-matched-path')).toBe(targetPath + '.action');
+      expect(res.headers.get('content-type')).toBe('text/x-component');
+      if (runtime === 'node') {
+        expect(res.headers.get('x-vercel-cache')).toBe('MISS');
+      } else {
+        expect(res.headers.get('x-edge-runtime')).toBe('1');
+      }
+    });
   });
 
   describe('pages', () => {

packages/next/test/fixtures/00-app-dir-actions-experimental-streaming/next.config.js

@@ -1 +1,14 @@
-module.exports = {};
+module.exports = {
+  rewrites() {
+    return [
+      {
+        source: '/rewrite/rsc/static',
+        destination: '/rsc/static',
+      },
+      {
+        source: '/rewrite/edge/rsc/static',
+        destination: '/edge/rsc/static',
+      },
+    ];
+  },
+};