fix: handle optional catchall parameters properly when deployed

[wyattjoh]

Previously, we had code responsible for parsing and handling the x-now-route-matches header (sent by Vercel) that included the route matches used for parameter parsing that only read from the named parameters if they were all present. This doesn't apply to routes with optional parameters (such as [[...rest]]), so it wasn't utilizing that matching mechanism. It previously fell back onto the second stage of parsing that utilized numeric based group matching, but this was recently changed on Vercel, so the fallback no longer applies for Next.js applications that are running on 15+.

Closes https://linear.app/vercel/issue/NEXT-3948

[wyattjoh]

• fix: handle optional catchall parameters properly when deployed #74562 👈 (View in Graphite)
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[ijjk]

Tests Passed

[ijjk]

Stats from current PR

Default Build (Increase detected ⚠️)

General Overall increase ⚠️

	vercel/next.js canary	vercel/next.js 01-06-fix_handle_optional_catchall_parameters_properly_on_vercel	Change
buildDuration	31.8s	27.5s	N/A
buildDurationCached	32.8s	25.1s	N/A
nodeModulesSize	417 MB	417 MB	N/A
nextStartRea..uration (ms)	738ms	848ms	⚠️ +110ms

Client Bundles (main, webpack)

	vercel/next.js canary	vercel/next.js 01-06-fix_handle_optional_catchall_parameters_properly_on_vercel	Change
1187-HASH.js gzip	52.6 kB	52.6 kB	N/A
8276.HASH.js gzip	169 B	168 B	N/A
8377-HASH.js gzip	5.44 kB	5.44 kB	N/A
bccd1874-HASH.js gzip	53 kB	53 kB	N/A
framework-HASH.js gzip	57.5 kB	57.5 kB	N/A
main-app-HASH.js gzip	232 B	235 B	N/A
main-HASH.js gzip	34.1 kB	34.1 kB	N/A
webpack-HASH.js gzip	1.71 kB	1.71 kB	N/A
Overall change	0 B	0 B	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	vercel/next.js 01-06-fix_handle_optional_catchall_parameters_properly_on_vercel	Change
polyfills-HASH.js gzip	39.4 kB	39.4 kB	✓
Overall change	39.4 kB	39.4 kB	✓

Client Pages

	vercel/next.js canary	vercel/next.js 01-06-fix_handle_optional_catchall_parameters_properly_on_vercel	Change
_app-HASH.js gzip	193 B	193 B	✓
_error-HASH.js gzip	193 B	193 B	✓
amp-HASH.js gzip	512 B	510 B	N/A
css-HASH.js gzip	343 B	342 B	N/A
dynamic-HASH.js gzip	1.84 kB	1.84 kB	✓
edge-ssr-HASH.js gzip	265 B	265 B	✓
head-HASH.js gzip	363 B	362 B	N/A
hooks-HASH.js gzip	393 B	392 B	N/A
image-HASH.js gzip	4.57 kB	4.57 kB	N/A
index-HASH.js gzip	268 B	268 B	✓
link-HASH.js gzip	2.35 kB	2.34 kB	N/A
routerDirect..HASH.js gzip	328 B	328 B	✓
script-HASH.js gzip	397 B	397 B	✓
withRouter-HASH.js gzip	323 B	326 B	N/A
1afbb74e6ecf..834.css gzip	106 B	106 B	✓
Overall change	3.59 kB	3.59 kB	✓

Client Build Manifests

	vercel/next.js canary	vercel/next.js 01-06-fix_handle_optional_catchall_parameters_properly_on_vercel	Change
_buildManifest.js gzip	749 B	747 B	N/A
Overall change	0 B	0 B	✓

Rendered Page Sizes

	vercel/next.js canary	vercel/next.js 01-06-fix_handle_optional_catchall_parameters_properly_on_vercel	Change
index.html gzip	523 B	523 B	✓
link.html gzip	539 B	537 B	N/A
withRouter.html gzip	519 B	520 B	N/A
Overall change	523 B	523 B	✓

Edge SSR bundle Size

	vercel/next.js canary	vercel/next.js 01-06-fix_handle_optional_catchall_parameters_properly_on_vercel	Change
edge-ssr.js gzip	128 kB	128 kB	N/A
page.js gzip	206 kB	206 kB	N/A
Overall change	0 B	0 B	✓

Middleware size

	vercel/next.js canary	vercel/next.js 01-06-fix_handle_optional_catchall_parameters_properly_on_vercel	Change
middleware-b..fest.js gzip	668 B	669 B	N/A
middleware-r..fest.js gzip	155 B	156 B	N/A
middleware.js gzip	31.2 kB	31.2 kB	N/A
edge-runtime..pack.js gzip	844 B	844 B	✓
Overall change	844 B	844 B	✓

Next Runtimes

	vercel/next.js canary	vercel/next.js 01-06-fix_handle_optional_catchall_parameters_properly_on_vercel	Change
274-experime...dev.js gzip	322 B	322 B	✓
274.runtime.dev.js gzip	314 B	314 B	✓
app-page-exp...dev.js gzip	364 kB	364 kB	✓
app-page-exp..prod.js gzip	129 kB	129 kB	✓
app-page-tur..prod.js gzip	142 kB	142 kB	✓
app-page-tur..prod.js gzip	138 kB	138 kB	✓
app-page.run...dev.js gzip	352 kB	352 kB	✓
app-page.run..prod.js gzip	125 kB	125 kB	✓
app-route-ex...dev.js gzip	37.5 kB	37.5 kB	✓
app-route-ex..prod.js gzip	25.6 kB	25.6 kB	✓
app-route-tu..prod.js gzip	25.6 kB	25.6 kB	✓
app-route-tu..prod.js gzip	25.4 kB	25.4 kB	✓
app-route.ru...dev.js gzip	39.2 kB	39.2 kB	✓
app-route.ru..prod.js gzip	25.4 kB	25.4 kB	✓
pages-api-tu..prod.js gzip	9.69 kB	9.69 kB	✓
pages-api.ru...dev.js gzip	11.6 kB	11.6 kB	✓
pages-api.ru..prod.js gzip	9.68 kB	9.68 kB	✓
pages-turbo...prod.js gzip	21.7 kB	21.7 kB	✓
pages.runtim...dev.js gzip	27.5 kB	27.5 kB	✓
pages.runtim..prod.js gzip	21.7 kB	21.7 kB	✓
server.runti..prod.js gzip	916 kB	916 kB	N/A
Overall change	1.53 MB	1.53 MB	✓

build cache Overall increase ⚠️

	vercel/next.js canary	vercel/next.js 01-06-fix_handle_optional_catchall_parameters_properly_on_vercel	Change
0.pack gzip	2.08 MB	2.08 MB	N/A
index.pack gzip	74.1 kB	74.9 kB	⚠️ +758 B
Overall change	74.1 kB	74.9 kB	⚠️ +758 B

Diff details

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Commit: d2eb952

[eps1lon]

types are complaining.

Can we add a normal e2e test as well? That would be tested on vercel.com via deploy test nowadays so it should fail without this change.

[eps1lon]

Would it have been possible for other hosting providers to massage x-now-route-matches to work around this bug?

[eps1lon]

So we already had test showing symptoms of the bug?

[wyattjoh]

This is specific to the way that Vercel handles the matches. We used to previously support both the index based and name based matches, but this isn't supported on Vercel anymore, which is what I suspect cause this to surface.