fix(routing): match inherited slot params against routePath, not request.url

[james-elicx]

Follow-up to #1039, addressing two items I missed during review.

Summary

• Bug under basePath: buildSlotOverrides was deriving the URL parts to match against slot.slotPatternParts from request.url. The original request URL still carries the configured basePath, but slotPatternParts is built from app-relative segments only — so for any basePath-configured app, the pattern match silently failed and slot params fell back to the route's matched params (the exact bug fix(routing): mirror inherited parallel slots to descendant sub-pages #1039 was supposed to fix). Switched to the already-normalized routePath parameter (basePath stripped, RSC suffix removed) that buildPageElements already receives.
• Memoize findSlotSubPages: cached per-build via a WeakMap keyed by the matcher. Inherited slots get scanned once per descendant route, so without memoization a route N segments deep paid O(N) full subtree walks for every shared ancestor slot. Cache lifetime tracks the matcher (one per build), so a long-lived dev server doesn't accumulate state across builds.
• Dedupe: findMirroredSlotPage was calling convertSegmentsToRouteParts(segmentsBelow) twice when the literal-tier match missed. Hoisted it out so both tiers reuse the conversion.

Test plan

• New unit test in tests/app-page-element-builder.test.ts exercises the basePath regression: request URL is http://localhost/base/distinct/alice while routePath is /distinct/alice, slot has slotPatternParts: ["distinct", ":name"]. Without the fix, urlParts would be ["base","distinct","alice"], the match would fail, and the slot's resolved params would silently lose the name value. With the fix, slotParams resolves to { name: "alice" }.
• pnpm exec vp test run --project unit — 3524 tests pass.
• pnpm check — only pre-existing failure (benchmarks/vinext/vite.config.ts cannot resolve vinext until the package is built; same on main).

🤖 Generated with Claude Code

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/vinext@1040

commit: f35c27b

[james-elicx]

/bigbonk review

[github-actions]

Example	Preview	Production	Original
app-router-cloudflare	preview	production
pages-router-cloudflare	preview	production
app-router-playground	preview	production	original
realworld-api-rest	preview	production
nextra-docs-template	preview	production
benchmarks	preview	production
hackernews	preview	production	original

[ask-bonk]

Clean follow-up. All three changes are correct and well-tested.

basePath fix — The root cause was straightforward: buildSlotOverrides was parsing request.url to get URL parts for matching against slotPatternParts, but slotPatternParts are app-relative (basePath already stripped during graph build). The routePath parameter is already the normalized form (basePath stripped, RSC suffix removed), so switching to it is the right fix. The new test directly exercises this by setting request.url to http://localhost/base/distinct/alice while routePath is /distinct/alice, proving the old code would have produced ["base","distinct","alice"] and silently failed the match.

Memoization — findSlotSubPages does synchronous fs.readdirSync + fs.existsSync walks, so caching per (matcher, slotDir) is a clear win for routes with deep inherited slot chains. The WeakMap<ValidFileMatcher, ...> keying is appropriate since ValidFileMatcher is an object created once per build (via createValidFileMatcher), and the cache naturally dies when the matcher is GC'd. Both call sites (line 332 in discoverSlotSubRoutes and line 907 in findMirroredSlotPage) only iterate the returned array without mutating it, so sharing the cached reference is safe.

Dedupe — Hoisting convertSegmentsToRouteParts above both tiers in findMirroredSlotPage is a trivial but correct cleanup. The conversion only depends on segmentsBelow which doesn't change between tiers.

CI is all green. Ship it.

[ask-bonk]

Approved PR #1040. All three changes are correct:

1. basePath fix — buildSlotOverrides now uses the already-normalized routePath instead of re-parsing request.url, which would re-introduce the basePath prefix and silently break slot param matching.

2. Memoization — findSlotSubPages caches results in a WeakMap keyed by matcher, avoiding redundant filesystem walks for deep inherited slot chains. Both callers only iterate the returned array (no mutation), so sharing is safe.

3. Dedupe — convertSegmentsToRouteParts hoisted above both tiers in findMirroredSlotPage to avoid the redundant second call.

CI is all green across all 30 checks.

github run