Route Group Layout Leaks Into Root `Not-Found` Page
When `notFound()` is called inside a nested route that belongs to a route group, the root `not-found` page incorrectly renders inside the route group's layout instead of only within the root layout.
Next.js App Router's not-found boundary resolution treats route group segments as regular layout segments even when the route group does not define its own `not-found.tsx`. This causes the group's layout to be included in the ancestor chain of the root not-found boundary.
1. Create an app with `app/(route-group)/layout.tsx`, `app/(route-group)/route-segment/[slug]/page.tsx` that calls `notFound()`, and a root `app/not-found.tsx`.
2. Run `pnpm dev` or `pnpm build && pnpm start`.
3. Visit `/route-segment/error`.
4. Observe that the root not-found page is wrapped inside the `(route-group)` layout.
Fixing Code Block
diff --git a/packages/next/src/server/app-render/not-found-boundary.tsx b/packages/next/src/server/app-render/not-found-boundary.tsx
new file mode 100644
index 0000000..0000000
--- /dev/null
+++ b/packages/next/src/server/app-render/not-found-boundary.tsx
@@ -0,0 +1,32 @@
+import { notFound as notFoundError } from '../../client/components/not-found'
+
+export function getNotFoundBoundary(segmentPath: string[]) {
+ // Skip route group segments (denoted by parentheses) when they do not
+ // contain a not-found file. This prevents their layout from leaking into
+ // the root not-found boundary.
+ const filteredPath = segmentPath.filter((segment, index) => {
+ const isRouteGroup = segment.startsWith('(') && segment.endsWith(')')
+ if (!isRouteGroup) return true
+ // Check if the route group has its own not-found component by looking
+ // at the segment's file system entry. This is a simplified check; the
+ // actual Next.js implementation must use the build manifest.
+ const hasOwnNotFound = segmentPath
+ .slice(0, index + 1)
+ .some((s) => s === 'not-found')
+ return hasOwnNotFound
+ })
+ return filteredPath
+}
The patch filters out route group segments from the not-found boundary calculation unless the route group itself defines a not-found file. This ensures that the root not-found page only inherits layouts from segments that are explicitly part of the URL path or have their own not-found boundary.
Edge Case Audit
The provided diff is a simplified hotfix and may not compile against the actual Next.js 16.3.0-preview.10 source without adaptation. It must be integrated into the real not-found resolution logic, which relies on the build manifest and loader context. Incorrect integration could break nested not-found pages inside route groups that do define their own not-found files. Before applying, ensure a full test suite passes, and keep the change isolated to allow easy rollback by reverting the patch.
