Optional catch-all `[[...slug]]` does not serve the root `/` (empty params) → 404

[hyf0]

Problem

vinext does not serve the root / of an optional catch-all route pages/[[...slug]].js.

react.dev serves nearly everything from src/pages/[[...markdownPath]].js. Its getStaticPaths emits { markdownPath: [] } for src/content/index.md (the homepage). Under Next this serves /. Under vinext, the optional catch-all is converted to /:markdownPath* but the empty-params root is not served.

Repro

• curl -i http://localhost:3000/ → 404 (serves the 404 page; og:title="Not Found").
• curl -i http://localhost:3000/_next/data/<id>/index.json → 404.
• Every non-root path (/learn, /reference/...) → 200, so it's specific to the empty-params root.

Workaround used

Convert the optional catch-all to a required catch-all [...markdownPath].js (which no longer matches /), filter the empty entry out of getStaticPaths, add an explicit pages/index.js re-exporting default + getStaticProps, and make context.params?.markdownPath null-safe (vinext passes params === null for the static / route).

Suggested fix

An optional catch-all [[...slug]] should match / with empty params, like Next.js.

[hyf0]

🔎 Triage — Next.js behavior vs vinext behavior

Method: grounded in the installed Next.js 15.1.12 source (node_modules/next/dist) and the exact vinext 0.1.8 dist (node_modules/vinext/dist) this issue was filed against; each conclusion independently re-checked by an adversarial second pass. vinext targets the Next.js 16 API surface, so a possible version difference was tested explicitly.

Verdict: 🐞 vinext bug (parity gap — fix needed) · should vinext fix: yes · scope: runtime-parity · confidence: high

Next.js behavior

Next.js's optional catch-all [[...slug]] matches the root "/". getRouteRegex emits the parameterized route (?:/(.+?))? wrapped as ^(?:/(.+?))?(?:/)?$, which matches "/". At runtime its matcher leaves the slug param UNSET for the empty root (the capture group is undefined, so if (m !== undefined) skips it) — i.e. Next's runtime params for "/" are also {}. For SSG, getStaticPaths returning { params: { slug: [] } } produces the prerendered pathname "/" (empty array → no segments), and Next serves that path by matching the request PATHNAME against its prerendered/static set — it does not re-run getStaticPaths and compare param objects at request time. Net result: GET / → 200 served by the optional catch-all with empty params. This has been stable since ~Next 9.

_{Evidence: node_modules/next/dist/shared/lib/router/utils/route-regex.js:100 (optional catch-all -> '(?:/(.+?))?') · node_modules/next/dist/shared/lib/router/utils/route-regex.js:108-114 (getRouteRegex wraps as ^...(?:/)?$, matches '/') · node_modules/next/dist/shared/lib/router/utils/route-matcher.js:30 (param only set when capture !== undefined; root yields no slug key)}

vinext behavior

vinext's request-time route trie correctly MATCHES the root "/" to the optional catch-all route (route-trie.js:105-108 returns optionalCatchAllChild.route), but that terminal branch returns buildParams([]) = {} WITHOUT setting the catch-all key to [] (unlike the non-root branch at route-trie.js:132-138 which sets params[paramName] = urlParts.slice(index)). The matched params {} flow unchanged through pages-page-handler.js:122,218 into resolvePagesPageData. There (pages-page-data.js:234-241) vinext re-runs getStaticPaths at request time and validates via matchesPagesStaticPath: for entry { params: { markdownPath: [] } } and actual params {}, it evaluates Array.isArray(actual) && value.join('/') === actual.join('/') where actual = params['markdownPath'] = undefined, so Array.isArray(undefined) is false → the entry does not match → isValidPath = false. With fallback === false, line 241 returns buildPagesNotFoundResult → 404 for the HTML page (kind:'notFound' → 404 page) and for /_next/data//index.json (kind:'response' → 404 JSON). Every non-root path works because the trie's non-terminal branch sets markdownPath to a non-empty array that join-compares equal to the getStaticPaths entry.

_{Evidence: node_modules/vinext/dist/routing/route-trie.js:100-109 (terminal/root optional-catch-all match returns buildParams(entries) with no empty-array param) · node_modules/vinext/dist/routing/route-trie.js:132-138 (non-root branch DOES set params[paramName]=urlParts.slice(index)) · node_modules/vinext/dist/server/pages-page-data.js:240-241 (isValidPath via matchesPagesStaticPath; fallback===false && !isValidPath returns 404) · node_modules/vinext/dist/server/pages-page-data.js:146-155 (matchesPagesStaticPath: Array.isArray(actual) check fails when actual is undefined for empty root) · node_modules/vinext/dist/server/pages-page-handler.js:122 and 218 (matched params passed unchanged into resolvePagesPageData) · node_modules/vinext/dist/routing/route-pattern.js:4 (([[...x]]) -> :x*) and 27-33 (fillRoutePatternSegments yields '/' for empty params)}

Is it a version difference (vinext → Next 16 vs react.dev → Next 15)?

No. Next.js optional catch-all matching the root '/' with empty params is stable since ~Next 9 — the route-regex (?:/(.+?))? form and the prerender-by-pathname SSG model are unchanged across Next 13-16. The installed Next 15.1.12 source (route-regex.js:100, route-matcher.js:30) shows exactly this behavior, and there is no Next 15->16 changelog entry altering optional-catch-all root matching. The divergence is not from vinext targeting Next 16; it is a vinext implementation defect in request-time getStaticPaths param re-validation.

Fix

dist/server/pages-page-data.js — matchesPagesStaticPath (146-155) / the isValidPath check at resolvePagesPageData (240-241): treat a missing/undefined actual param as equivalent to an empty array when the getStaticPaths entry value is []. Equivalently/additionally dist/routing/route-trie.js:105-108: populate params[optionalCatchAllChild.paramName]=[] for the empty-root optional-catch-all match so the matched param representation matches the getStaticPaths entry.

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_{🤖 Triaged with Claude Code (Opus 4.8) — read-only analysis against installed Next 15.1.12 + vinext 0.1.8 sources, adversarially verified.}

[hyf0]

Fixed upstream: cloudflare/vinext#2238 (fix(pages): match optional catch-all prerender paths), released in vinext 0.2.0 — the optional catch-all now serves the empty-params root /.

This port keeps the required-catch-all + explicit index.js shape (valid in both Next.js and vinext), so no revert is required. Closing as fixed.