fix(nextjs): Fix parameterization for root catchall routes (#17489)

Author: mjq

packages/nextjs/src/config/manifest/createRouteManifest.ts

@@ -77,10 +77,16 @@ function buildRegexForDynamicRoute(routePath: string): { regex: string; paramNam
 
   let pattern: string;
   if (hasOptionalCatchall) {
-    // For optional catchall, make the trailing slash and segments optional
-    // This allows matching both /catchall and /catchall/anything
-    const staticParts = regexSegments.join('/');
-    pattern = `^/${staticParts}(?:/(.*))?$`;
+    if (regexSegments.length === 0) {
+      // If the optional catchall happens at the root, accept any path starting
+      // with a slash. Need capturing group for parameter extraction.
+      pattern = '^/(.*)$';
+    } else {
+      // For optional catchall, make the trailing slash and segments optional
+      // This allows matching both /catchall and /catchall/anything
+      const staticParts = regexSegments.join('/');
+      pattern = `^/${staticParts}(?:/(.*))?$`;
+    }
   } else {
     pattern = `^/${regexSegments.join('/')}$`;
   }

packages/nextjs/test/config/manifest/suites/catchall-at-root/app/[[...path]]/page.tsx

@@ -0,0 +1 @@
+// beep

packages/nextjs/test/config/manifest/suites/catchall-at-root/app/page.tsx

@@ -0,0 +1 @@
+// Ciao

packages/nextjs/test/config/manifest/suites/catchall-at-root/catchall-at-root.test.ts

@@ -0,0 +1,30 @@
+import path from 'path';
+import { describe, expect, test } from 'vitest';
+import { createRouteManifest } from '../../../../../src/config/manifest/createRouteManifest';
+
+describe('catchall', () => {
+  const manifest = createRouteManifest({ appDirPath: path.join(__dirname, 'app') });
+
+  test('should generate a manifest with catchall route', () => {
+    expect(manifest).toEqual({
+      staticRoutes: [{ path: '/' }],
+      dynamicRoutes: [
+        {
+          path: '/:path*?',
+          regex: '^/(.*)$',
+          paramNames: ['path'],
+        },
+      ],
+    });
+  });
+
+  test('should generate correct pattern for catchall route', () => {
+    const catchallRoute = manifest.dynamicRoutes.find(route => route.path === '/:path*?');
+    const regex = new RegExp(catchallRoute?.regex ?? '');
+    expect(regex.test('/123')).toBe(true);
+    expect(regex.test('/abc')).toBe(true);
+    expect(regex.test('/123/456')).toBe(true);
+    expect(regex.test('/123/abc/789')).toBe(true);
+    expect(regex.test('/')).toBe(true);
+  });
+});