fix(effect): TMap.remove/removeAll clears entire bucket on hash collision - #6233
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…sion The fixed code in tMap.ts had two related bugs: 1. The destructuring of Chunk.partition was reversed (toRemove/toRetain swapped) 2. The predicate compared entry[1] (value) to key instead of entry[0] (key) Together these caused removing one key with a hash collision to drop every other entry in the same bucket. Added regression tests using a CollidingKey type that forces every entry into one bucket. Fixes Effect-TS#6225
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Summary
TMap.removeandTMap.removeAllwere clearing every entry in a bucket whenever two keys hashed to the same slot. The fix is a 2-line change inpackages/effect/src/internal/stm/tMap.ts.Why this matters
Bucket-level data loss on hash collision is a correctness bug for any user storing entries whose key types collide (custom
Hashimplementations, value types with low-entropy hashes). The bug was reported in #6225 with a minimal repro showing three entries in a single bucket where removing one drops the other two. The fixed code has two related issues:Chunk.partitionreturns[predicate-true, predicate-false]. The destructuringconst [toRemove, toRetain] = ...was backwards.Equal.equals(entry[1], key), comparing the entry's value against the key instead of the entry's key (entry[0]).Together these meant the code was retaining the matched key and removing every other key in the bucket.
Changes
packages/effect/src/internal/stm/tMap.ts- swap the destructuring to[toRetain, toRemove]and compareentry[0](key) against the key in bothremoveandremoveAll.packages/effect/test/TMap.test.ts- add two regression tests using aCollidingKeytype whoseHashalways returns 1, forcing every entry into one bucket..changeset/fix-tmap-remove-colliding-keys.md- patch-level changeset.Testing
pnpm test --filter=effect -- TMap.test(Vitest). The newremove - preserves colliding keysandremoveAll - preserves colliding keystests fail onmainand pass with the fix.Fixes #6225