fix(react): Defer React Router span finalization until lazy routes load #18881
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onurtemizkan
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Pull request overview
This PR fixes a critical issue where pageload transactions receive incorrect names (URL-based or wildcard-based) when lazy routes load after the span ends due to idle timeout. The fix introduces a deferred promise mechanism to block span finalization until patchRoutesOnNavigation completes, ensuring lazy-loaded routes are available for proper transaction naming.
Changes:
- Added deferred promise mechanism that blocks span finalization until lazy routes finish loading via
patchRoutesOnNavigation - Captured active span before router creation (instead of after) to maintain reference even if span ends before lazy routes load
- Modified
patchSpanEndto use globalallRoutesSet directly instead of a snapshot, allowing visibility of routes added after span starts - Extended
patchRoutesOnNavigationwrapper to handle both pageload and navigation spans (previously only navigation)
Reviewed changes
Copilot reviewed 5 out of 5 changed files in this pull request and generated 9 comments.
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| File | Description |
|---|---|
packages/react/src/reactrouter-compat-utils/instrumentation.tsx |
Core implementation: adds deferred promise mechanism, moves span capture timing, updates patchSpanEnd to use global allRoutes, extends patchRoutesOnNavigation to handle pageload spans |
packages/react/test/reactrouter-compat-utils/instrumentation.test.tsx |
Unit tests verifying allRoutes global set behavior and proper handling of late route additions |
dev-packages/e2e-tests/test-applications/react-router-7-lazy-routes/tests/transactions.test.ts |
E2E regression tests verifying slow lazy routes get parameterized names even with early span end |
dev-packages/e2e-tests/test-applications/react-router-7-lazy-routes/src/pages/WildcardLazyRoutes.tsx |
New test component simulating slow lazy route loading with wildcard routes |
dev-packages/e2e-tests/test-applications/react-router-7-lazy-routes/src/index.tsx |
Router configuration for wildcard lazy route test scenario |
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packages/react/src/reactrouter-compat-utils/instrumentation.tsx
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...ages/e2e-tests/test-applications/react-router-7-lazy-routes/src/pages/WildcardLazyRoutes.tsx
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chargome
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Jan 21, 2026
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chargome
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chargome
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Looks good but the code for this becomes increasingly difficult to read. We should add a state/mermaid diagram at some point for more clarity on how we do parameterization here
Thanks for fixing!
s1gr1d
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Jan 21, 2026
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| for (const route of allRoutes) { | ||
| const idMatches = route.id !== undefined && route.id === routeId; | ||
| const referenceMatches = route === leafRoute; | ||
| const pathMatches = | ||
| route.path !== undefined && leafRoute.path !== undefined && route.path === leafRoute.path; | ||
|
|
||
| if (idMatches || referenceMatches || pathMatches) { | ||
| // Attach children to this parent route | ||
| addResolvedRoutesToParent(children, route); | ||
| break; | ||
| } | ||
| } |
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You could use .find() here (fewer bytes in bundle size and readable):
const matchingRoute = allRoutes.find(route => {
const idMatches = route.id !== undefined && route.id === routeId;
const referenceMatches = route === leafRoute;
const pathMatches = route.path !== undefined && leafRoute.path !== undefined && route.path === leafRoute.path;
return idMatches || referenceMatches || pathMatches;
});
if (matchingRoute) {
addResolvedRoutesToParent(children, targetRoute);
}
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Author
I agree, I'll add a dev-docs with diagrams after we're eventually sure we eliminated all potential edge cases. |
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node-overhead report 🧳Note: This is a synthetic benchmark with a minimal express app and does not necessarily reflect the real-world performance impact in an application.
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Following up on #18155 and #18346
Fixes an issue where pageload transactions have incorrect names (URL-based or wildcard-based) when lazy routes load after the span ends due to idle timeout.
This occurs when using patchRoutesOnNavigation for lazy route loading. The idle timeout can fire before lazy routes finish loading, causing the span to end with a wildcard like
/slow-fetch/*instead of the parameterized/slow-fetch/:id.The root cause was that the active span was captured after router creation, making it inaccessible when
patchRoutesOnNavigationwas called later (span already ended). Also,patchSpanEndwas taking a snapshot ofallRoutes, so lazy routes added later wouldn't be visible.This fix:
wrapPatchRoutesOnNavigationpatchRoutesOnNavigationcompletesallRoutesSet directly instead of a snapshotpatchRoutesOnNavigation(was only handling navigation before)