fix(react-router): walk parent route chain for notFoundComponent lookup

[davidclimbing]

What Changed

Refactored new-process-route-tree.ts to ensure pathless routes (e.g., _authenticated) are correctly processed during fuzzy matching, allowing their notFoundComponent to trigger.

Files Changed:

• packages/router-core/src/new-process-route-tree.ts
  • Removed skipOnParamError guard for pathless node creation.
  • Added explicit node.route assignment to pathless nodes.

Why

**Fixes #6351 **

Pathless layout routes were being skipped during fuzzy matching when a child route failed to match. This prevented their notFoundComponent from rendering, causing the error to bubble up to the root incorrectly.

This change ensures pathless nodes are properly flagged in the segment tree so they are considered valid candidates for handling notFound errors.

How Tested

New Tests:

• Added packages/router-core/tests/pathless_fuzzy_matching.test.ts to verify:
  • Exact matching works for children.
  • Fuzzy matching correctly finds the pathless layout for missing paths.

Results:

• ✅ All new tests passed.
• ✅ All 846 regression tests in router-core passed.

**Closes #6351 **

Summary by CodeRabbit

• Bug Fixes

  • Not-found handling now searches up the route hierarchy to render the nearest ancestor's not-found component when a child lacks one, improving fallback behavior for nested routes.

• Tests

  • Added test confirming pathless layout routes inherit and use a parent's not-found component instead of the global default.

_{✏️ Tip: You can customize this high-level summary in your review settings.}

[coderabbitai]

📝 Walkthrough

Walkthrough

This PR changes not-found resolution to traverse up the route hierarchy to find the nearest route with a notFoundComponent, preferring that ancestor component, then the router's defaultNotFoundComponent, and finally the global default. The renderRouteNotFound signature now receives router as the first parameter. A test was added validating a pathless layout's notFound is used for children.

Changes

Cohort / File(s)	Summary
Not-Found Resolution Logic packages/react-router/src/renderRouteNotFound.tsx	Signature changed to renderRouteNotFound(router, route, data). Adds traversal (routeWithNotFound + while loop) to locate nearest ancestor with notFoundComponent. Renders ancestor's notFoundComponent if found; otherwise falls back to router.defaultNotFoundComponent or DefaultGlobalNotFound. Removes immediate dev warning and silences previous warning behavior.
Test Coverage packages/react-router/tests/not-found.test.tsx	New test: "pathless layout route notFoundComponent is used when child has none (issue #6351)". Builds nested routes (root layout → authenticated layout with notFoundComponent → agents children), navigates to a missing child path, and asserts the authenticated layout's notFound component is rendered instead of router default.

Sequence Diagram(s)

mermaid
sequenceDiagram
participant Client as Client
participant Router as Router
participant RenderFn as renderRouteNotFound
participant RouteChain as Route Hierarchy
participant DefaultGlobal as DefaultGlobalNotFound
Client->>Router: navigate to /agents/non-existent
Router->>RenderFn: renderRouteNotFound(router, route, data)
RenderFn->>RouteChain: traverse ancestors for notFoundComponent
alt ancestor with notFoundComponent found
RouteChain->>RenderFn: return ancestor.notFoundComponent
RenderFn->>Client: render ancestor.notFoundComponent
else no ancestor notFoundComponent
RenderFn->>Router: check router.defaultNotFoundComponent
alt router.defaultFound present
Router->>RenderFn: return router.defaultNotFoundComponent
RenderFn->>Client: render router.defaultNotFoundComponent
else
RenderFn->>DefaultGlobal: use DefaultGlobalNotFound
RenderFn->>Client: render DefaultGlobalNotFound
end
end

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

• fix: update error handling in MatchInner to access error data directly #4746 — Modifies packages/react-router/src/renderRouteNotFound.tsx (changes to not-found props passing and related typing).
• chore: Fixed the defaultNotFoundComponent as guided by #5757 #5937 — Adjusts renderRouteNotFound warnings/default markup; related to not-found rendering control flow.

Suggested reviewers

• schiller-manuel
• Sheraff

Poem

🐰 I hopped the route tree, nose in the wind,
Found parent notFound where child had thinned,
No panic, no default pulled from afar—
Ancestors now answer when routes stray or spar. 🥕✨

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	Title accurately describes the main change: refactoring renderRouteNotFound to traverse the parent route chain for notFoundComponent lookup instead of checking only the current route.
Linked Issues check	✅ Passed	The PR successfully addresses issue #6351 by modifying renderRouteNotFound to search up the route hierarchy for notFoundComponent, enabling pathless layout routes to have their notFoundComponent rendered before falling back to the global default.
Out of Scope Changes check	✅ Passed	All changes are directly related to the stated objective: modifications to renderRouteNotFound signature and implementation in react-router package, and a new regression test validating the fix.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing touches

• 📝 Generate docstrings

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[nx-cloud]

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---

☁️ Nx Cloud last updated this comment at 2026-01-22 17:20:51 UTC

[pkg-pr-new]

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commit: 14bfa97

[Sheraff]

Thank your for your PR, the issue is clear and based on the video (#6351 (comment)) it does seem like a real bug to me.

However:

1. in the test you are proposing in this PR, I would disagree that _layout should be fuzzy matched

In the video example we have these routes

__root__
  _authenticated
    agents.route
      skill-agent.index

So when the path to match is /agents/foo, then skill-agent.index is not matched, but agents.route should be (so the notFoundComponent in _authenticated should be used).

But in your case

__root__
  _layout
    child

matching /missing does not match child at all, so I don't see why it should include the _layout in its matched routes.

2. following this explanation, I'm not entirely sure the fix you are proposing is correct. It might be. But skipping some nodes in the tree is good for performance, so ideally I'd like to understand why getNodeMatch does not fuzzy match the agents.route in the video case. I haven't tried, but it feels like it should pass this condition

router/packages/router-core/src/new-process-route-tree.ts

Lines 1021 to 1029 in 17045eb

	// In fuzzy mode, track the best partial match we've found so far
	if (
	fuzzy &&
	node.route &&
	node.kind !== SEGMENT_TYPE_INDEX &&
	isFrameMoreSpecific(bestFuzzy, frame)
	) {
	bestFuzzy = frame
	}

[schiller-manuel]

this PR breaks a lot of tests. check the CI output

[davidclimbing]

2. following this explanation, I'm not entirely sure the fix you are proposing is correct. It might be. But skipping some nodes in the tree is good for performance, so ideally I'd like to understand why getNodeMatch does not fuzzy match the agents.route in the video case. I haven't tried, but it feels like it should pass this condition

Thank you @Sheraff for your patient feedback!

What was wrong with my previous approach

I realize now that my previous test case was incorrect, and I am sorry for any confusion this caused. As @Sheraff pointed out, the test was flawed because the /missing path was structured in a way that it didn't actually fall under the _layout (pathless route) hierarchy. This led me to mistakenly investigate new-process-route-tree.ts, which was not the source of the problem. Your feedback helped me realize that the issue was specifically about how the rendering layer identifies the correct notFoundComponent within a nested, pathless route structure.

Root cause analysis (Issue #6351)

The problem exists in the renderRouteNotFound() function. When a "Not Found" state occurs (e.g., navigating to /agents/non-existent):

1. The router correctly performs a fuzzy-match to the agents route.
2. The agents route itself does not have a notFoundComponent.
3. The Bug: Instead of traversing up to the immediate parent (the pathless _authenticated route), the code was skipping the parent hierarchy and falling back directly to the defaultNotFoundComponent defined in the root.
4. Expected: Even for pathless routes, the router should check the parent chain recursively to find the nearest available notFoundComponent.

The fix

I have updated renderRouteNotFound() to correctly walk up the parent route chain. This ensures that pathless layout routes (like _authenticated) are properly checked for their notFoundComponent before reaching the global default.

// Recursively walk up the parent route chain to find the nearest notFoundComponent
let routeWithNotFound: AnyRoute | undefined = route
while (routeWithNotFound && !routeWithNotFound.options.notFoundComponent) {
  routeWithNotFound = routeWithNotFound.parentRoute
}

Test case

I added a robust test case in packages/react-router/tests/not-found.test.tsx that mirrors the structure reported in issue #6351:

• Structure: __root__ → _authenticated (pathless) → agents → skill-agent
• Scenario: Navigate to /agents/non-existent.
• Verification: Confirms that _authenticated's notFoundComponent is rendered, ensuring pathless parents are no longer ignored.

Files changed

• packages/react-router/src/renderRouteNotFound.tsx - The fix
• packages/react-router/tests/not-found.test.tsx - Regression test for issue main.tsx defaultNotFound component is being rendered instead a root pathless route notFoundComponent #6351