fix default handling in route groups that handle interception

[ztanner]

What?

Navigating to a layout that is part of a route group that uses route interception currently will trigger a 404 error if the route group doesn't define a default segment.

Why?

When next-app-loader injects fallback defaults into the loader tree, it does so by first seeing if a default already exists. However it does this without ignoring route groups, meaning if you have a /app/default.tsx and your interception route is at /app/(level1)/(level2), it will look for the default at /app/(level1)/(level2)/default.tsx.

When a default isn't found, the fallback behavior is to trigger a notFound() error. This means navigating to the intercepting route that has no default for the children segment will 404.

How?

This adjusts the fallback behavior by attempting to find the default by normalizing the segment path, which will ignore route groups. That way /app/(level1)/(level2)/default will first check /app/default.tsx before falling back to notFound behavior.

Fixes #59279
Closes NEXT-1813

[ztanner]

Current dependencies on/for this PR:

• canary
  • PR fix default handling in route groups that handle interception #59752 👈

This stack of pull requests is managed by Graphite.

[ijjk]

Stats from current PR

Default Build

General Overall increase ⚠️

	vercel/next.js canary	vercel/next.js 12-18-fix_intercepting_route_behavior_in_route_groups	Change
buildDuration	12.6s	12.8s	⚠️ +244ms
buildDurationCached	7.2s	6.1s	N/A
nodeModulesSize	200 MB	200 MB	⚠️ +3.96 kB
nextStartRea..uration (ms)	428ms	422ms	N/A

Client Bundles (main, webpack)

	vercel/next.js canary	vercel/next.js 12-18-fix_intercepting_route_behavior_in_route_groups	Change
170-HASH.js gzip	26.8 kB	26.9 kB	N/A
199.HASH.js gzip	181 B	185 B	N/A
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main-app-HASH.js gzip	240 B	241 B	N/A
main-HASH.js gzip	31.7 kB	31.7 kB	N/A
webpack-HASH.js gzip	1.7 kB	1.7 kB	N/A
Overall change	98.5 kB	98.5 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	vercel/next.js 12-18-fix_intercepting_route_behavior_in_route_groups	Change
polyfills-HASH.js gzip	31 kB	31 kB	✓
Overall change	31 kB	31 kB	✓

Client Pages

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Client Build Manifests

	vercel/next.js canary	vercel/next.js 12-18-fix_intercepting_route_behavior_in_route_groups	Change
_buildManifest.js gzip	484 B	482 B	N/A
Overall change	0 B	0 B	✓

Rendered Page Sizes

	vercel/next.js canary	vercel/next.js 12-18-fix_intercepting_route_behavior_in_route_groups	Change
index.html gzip	529 B	526 B	N/A
link.html gzip	542 B	539 B	N/A
withRouter.html gzip	523 B	523 B	✓
Overall change	523 B	523 B	✓

Edge SSR bundle Size

	vercel/next.js canary	vercel/next.js 12-18-fix_intercepting_route_behavior_in_route_groups	Change
edge-ssr.js gzip	93.7 kB	93.7 kB	N/A
page.js gzip	146 kB	146 kB	N/A
Overall change	0 B	0 B	✓

Middleware size

	vercel/next.js canary	vercel/next.js 12-18-fix_intercepting_route_behavior_in_route_groups	Change
middleware-b..fest.js gzip	627 B	621 B	N/A
middleware-r..fest.js gzip	151 B	151 B	✓
middleware.js gzip	37.4 kB	37.4 kB	N/A
edge-runtime..pack.js gzip	1.92 kB	1.92 kB	✓
Overall change	2.07 kB	2.07 kB	✓

Next Runtimes

	vercel/next.js canary	vercel/next.js 12-18-fix_intercepting_route_behavior_in_route_groups	Change
app-page-exp...dev.js gzip	168 kB	168 kB	✓
app-page-exp..prod.js gzip	94.1 kB	94.1 kB	✓
app-page-tur..prod.js gzip	94.8 kB	94.8 kB	✓
app-page-tur..prod.js gzip	89.4 kB	89.4 kB	✓
app-page.run...dev.js gzip	138 kB	138 kB	✓
app-page.run..prod.js gzip	88.7 kB	88.7 kB	✓
app-route-ex...dev.js gzip	24 kB	24 kB	✓
app-route-ex..prod.js gzip	16.6 kB	16.6 kB	✓
app-route-tu..prod.js gzip	16.6 kB	16.6 kB	✓
app-route-tu..prod.js gzip	16.2 kB	16.2 kB	✓
app-route.ru...dev.js gzip	23.4 kB	23.4 kB	✓
app-route.ru..prod.js gzip	16.2 kB	16.2 kB	✓
pages-api-tu..prod.js gzip	9.37 kB	9.37 kB	✓
pages-api.ru...dev.js gzip	9.64 kB	9.64 kB	✓
pages-api.ru..prod.js gzip	9.37 kB	9.37 kB	✓
pages-turbo...prod.js gzip	21.9 kB	21.9 kB	✓
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pages.runtim..prod.js gzip	21.9 kB	21.9 kB	✓
server.runti..prod.js gzip	49.4 kB	49.4 kB	✓
Overall change	931 kB	931 kB	✓

Commit: 4fa3949

[ijjk]

Tests Passed

[loicnestler]

Any details on this PR will get merged and/or published to NPM? Is there a workaround for #59279 in the mean-time?

[ztanner]

@loicnestler you should be able to work around the issue in the above issue's reproduction by adding a default.tsx to your (level1)/(level2)/(level3) segment. This PR is essentially making sure that happens in case you have a root level default.tsx but not one defined in the route group.