fix(app-router): pass searchParams to layout generateMetadata

Layout `generateMetadata()` was always called with `undefined` for
`searchParams` because `spObj` (the URLSearchParams-to-plain-object
conversion) was constructed after the layout metadata loop. Hoist the
`spObj` construction to before the loop so every layout receives the
real query parameters — matching the behaviour already correct for the
page segment.

Adds a regression fixture (`layout-metadata-search`) and a test that
requests `/layout-metadata-search?tab=settings` and asserts the layout's
`generateMetadata` title reflects the query param value rather than the
undefined-fallback default.

Author: NathanDrake2406

packages/vinext/src/entries/app-rsc-entry.ts

@@ -955,6 +955,23 @@ async function buildPageElements(route, params, routePath, opts, searchParams) {
   // route it to the nearest error.tsx boundary (or global-error.tsx).
   const layoutMods = route.layouts.filter(Boolean);
 
+  // Convert URLSearchParams → plain object so we can pass it to
+  // resolveModuleMetadata (which expects Record<string, string | string[]>).
+  // Must be built before the layout loop so layouts receive the real searchParams.
+  // This same object is reused for pageProps.searchParams below.
+  const spObj = {};
+  let hasSearchParams = false;
+  if (searchParams && searchParams.forEach) {
+    searchParams.forEach(function(v, k) {
+      hasSearchParams = true;
+      if (k in spObj) {
+        spObj[k] = Array.isArray(spObj[k]) ? spObj[k].concat(v) : [spObj[k], v];
+      } else {
+        spObj[k] = v;
+      }
+    });
+  }
+
   // Build the parent promise chain and kick off metadata resolution in one pass.
   // Each layout module is called exactly once. layoutMetaPromises[i] is the
   // promise for layout[i]'s own metadata result.
@@ -966,7 +983,7 @@ async function buildPageElements(route, params, routePath, opts, searchParams) {
   for (let i = 0; i < layoutMods.length; i++) {
     const parentForThisLayout = accumulatedMetaPromise;
     // Kick off this layout's metadata resolution now (concurrent with others).
-    const metaPromise = resolveModuleMetadata(layoutMods[i], params, undefined, parentForThisLayout)
+    const metaPromise = resolveModuleMetadata(layoutMods[i], params, spObj, parentForThisLayout)
       .catch((err) => { console.error("[vinext] Layout generateMetadata() failed:", err); return null; });
     layoutMetaPromises.push(metaPromise);
     // Advance accumulator: resolves to merged(layouts[0..i]) once layout[i] is done.
@@ -977,22 +994,6 @@ async function buildPageElements(route, params, routePath, opts, searchParams) {
   // Page's parent is the fully-accumulated layout metadata.
   const pageParentPromise = accumulatedMetaPromise;
 
-  // Convert URLSearchParams → plain object so we can pass it to
-  // resolveModuleMetadata (which expects Record<string, string | string[]>).
-  // This same object is reused for pageProps.searchParams below.
-  const spObj = {};
-  let hasSearchParams = false;
-  if (searchParams && searchParams.forEach) {
-    searchParams.forEach(function(v, k) {
-      hasSearchParams = true;
-      if (k in spObj) {
-        spObj[k] = Array.isArray(spObj[k]) ? spObj[k].concat(v) : [spObj[k], v];
-      } else {
-        spObj[k] = v;
-      }
-    });
-  }
-
   const [layoutMetaResults, layoutVpResults, pageMeta, pageVp] = await Promise.all([
     Promise.all(layoutMetaPromises),
     Promise.all(layoutMods.map((mod) => resolveModuleViewport(mod, params).catch((err) => { console.error("[vinext] Layout generateViewport() failed:", err); return null; }))),

tests/app-router.test.ts

@@ -877,6 +877,19 @@ describe("App Router integration", () => {
     expect(html).toMatch(/name="description".*content="Read about my-post"/);
   });
 
+  it("layout generateMetadata() receives searchParams from URL query string", async () => {
+    // Regression test: layout generateMetadata() was always passed `undefined` for
+    // searchParams. Only page generateMetadata() received the real value.
+    const res = await fetch(`${baseUrl}/layout-metadata-search?tab=settings`);
+    expect(res.status).toBe(200);
+
+    const html = await res.text();
+    // The layout's generateMetadata reads searchParams.tab — should produce
+    // "Layout Section: settings", not "Layout Section: home" (the fallback for
+    // undefined searchParams).
+    expect(html).toContain("<title>Layout Section: settings</title>");
+  });
+
   it("renders catch-all routes with multiple segments", async () => {
     const res = await fetch(`${baseUrl}/docs/getting-started/install`);
     expect(res.status).toBe(200);

tests/fixtures/app-basic/app/layout-metadata-search/layout.tsx

@@ -0,0 +1,22 @@
+/**
+ * Regression fixture for layout generateMetadata searchParams bug.
+ *
+ * Before the fix, layout generateMetadata() always received `undefined`
+ * for searchParams — only page generateMetadata() received the real value.
+ */
+
+export async function generateMetadata({
+  searchParams,
+}: {
+  searchParams: Promise<{ tab?: string }>;
+}) {
+  const sp = await searchParams;
+  const tab = sp?.tab ?? "home";
+  return {
+    title: `Layout Section: ${tab}`,
+  };
+}
+
+export default function LayoutMetadataSearchLayout({ children }: { children: React.ReactNode }) {
+  return <div data-testid="layout-metadata-search-layout">{children}</div>;
+}

tests/fixtures/app-basic/app/layout-metadata-search/page.tsx

@@ -0,0 +1,8 @@
+export default function LayoutMetadataSearchPage() {
+  return (
+    <main data-testid="layout-metadata-search-page">
+      <h1>Layout Metadata Search Test</h1>
+      <p>This page tests that layout generateMetadata receives searchParams.</p>
+    </main>
+  );
+}