Give RouteCacheEntry a single hidden class across its lifecycle#96164
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Root cause
RouteCacheEntryobjects cycled through three hidden classes over their lifecycle, found by runningpnpm bench:deopt --scenario segment-cache: (A) the pending object literal increateDetachedRouteCacheEntry, which did not declarehasDynamicRewrite; (B) that shape plushasDynamicRewriteappended post-construction byfulfillRouteCacheEntry, a shape transition that also deprecates the original map; and (C) the two fulfilled-entry literals (deprecated_requestOptimisticRouteCacheEntryincache.tsand the synthetic entry inmatchKnownRouteinoptimistic-routes.ts) which declarehasDynamicRewritein a different key position, betweensupportsPerSegmentPrefetchingandrenderedSearch. Every property access on a route cache entry in the hot navigation/prefetch paths was therefore polymorphic.This PR pre-declares
hasDynamicRewrite: falseincreateDetachedRouteCacheEntryat the same key position as the fulfilled literals, collapsing all three shapes into one hidden class, and moves thehasDynamicRewrite: booleantype declaration fromFulfilledRouteCacheEntrytoRouteCacheEntrySharedto match. ThefulfilledEntry.hasDynamicRewrite = falsestore infulfillRouteCacheEntryis left in place; it is now an in-place store rather than a shape transition, and it re-clears the flag on re-fulfillment.Behavior neutrality
The field is pre-initialized to
falseon pending/empty entries and semantics are identical: no runtime code readshasDynamicRewritefrom an unfulfilled entry, and there are noinchecks,Object.keys, ordeleteoperations on these entries — only property reads.pnpm --filter=next typespasses with the field declared on the shared type.Verification
Measured with
pnpm bench:deopt --scenario segment-cache(fixture force-rebuilt against the patched build). ThehasDynamicRewritepolymorphic IC cleared, along with ~24 entry-field polymorphic IC lines acrossnavigation.ts,optimistic-routes.ts,scheduler.ts, andcache.ts(status, tree, canonicalUrl, renderedSearch, metadata, couldBeIntercepted, supportsPerSegmentPrefetching, staleAt, version, size). Totalic-polymorphicfindings dropped from 84 lines to 60. Results were confirmed stable across a second run.Before/after
findings.txtdiff:Two high-severity
wrong maplines remain and are explicitly NOT claimed by this PR: thecache-map.tsisValueExpiredline reads the intentionally 3-typed route|segment|bfcache map-value union, and theoptimistic-routes.tsresidual (now attributed to thehasDynamicRewriteread at 791:26) is a one-time map-deprecation deopt caused by in-place fulfillment generalizing null-initialized field types. The latter is tracked separately with a possible follow-up that fulfills entries via fresh literals instead of mutation.Tests
test/e2e/app-dir/segment-cache/optimistic-routing-rewrite-detection-regression(test-start-turbo): 3 passedtest/e2e/app-dir/segment-cache/staleness(test-start-turbo): 4 passed, 5 skipped (mode skips)Note on base branch