Check symbol-keyed properties in Match object patterns

[fubhy]

Summary

A valid typed object pattern whose only key is a symbol compiles as an empty conjunction and matches non-null objects that do not satisfy the symbol property's constraint.

Important

This PR starts with focused failing reproduction tests. Add the implementation fix to this same branch; CI is expected to fail until that fix is included.

Symbol-keyed object patterns match without checking the symbol

Module: Match
Audit ID: core-g-r-match-symbol-key-pattern-omitted
Severity / confidence: medium / high

What happens

A valid typed object pattern whose only key is a symbol compiles as an empty conjunction and matches non-null objects that do not satisfy the symbol property's constraint.

Why it happens

The runtime compiler enumerates pattern properties with Object.entries, which omits symbols. A symbol-only pattern therefore has no compiled predicates and accepts the wrong value.

Expected behavior

Types.PatternBase maps every key of a record-shaped value, including symbol keys, and a successful object-pattern match satisfies every supplied property constraint.

Relevant implementation

These links and excerpts are pinned to audit base c9b56ab507f224426ee8388dc450da447ec4715f.

• packages/effect/src/Match.ts:2234-2238
• packages/effect/src/internal/matcher.ts:126-145

View problematic code at packages/effect/src/Match.ts:2234-2238

  export type PatternBase<A> = A extends ReadonlyArray<infer _T> ? ReadonlyArray<any> | PatternPrimitive<A>
    : A extends Record<string, any> ? Partial<
        { [K in keyof A]: PatternPrimitive<A[K] & {}> | PatternBase<A[K] & {}> }
      >
    : never

View exact lines on GitHub

View problematic code at packages/effect/src/internal/matcher.ts:126-145

  } else if (pattern !== null && typeof pattern === "object") {
    const keysAndPredicates = Object.entries(pattern).map(
      ([k, p]) => [k, makePredicate(p)] as const
    )
    const len = keysAndPredicates.length

    return (u: unknown) => {
      if (typeof u !== "object" || u === null) {
        return false
      }

      for (let i = 0; i < len; i++) {
        const [key, predicate] = keysAndPredicates[i]
        if (!(key in u) || predicate((u as any)[key]) === false) {
          return false
        }
      }

      return true
    }

View exact lines on GitHub

Reproduction

pnpm vitest run packages/effect/test/Match.test.ts -t "checks symbol-keyed object pattern properties"

Observed failure: The intended failure was reproduced: the matcher returned "hit" instead of "miss".

Implementation handoff

The initial reproduction tests on this branch are the regression specification for the implementation fix that should follow in this PR.

1. Start with the pinned implementation excerpts and the Why it happens analysis above.
2. Change the implementation so it satisfies the stated Expected behavior; do not weaken or remove the reproduction assertions.
3. Run the focused reproduction command(s) and confirm the observed failures become passing tests:

pnpm vitest run packages/effect/test/Match.test.ts -t "checks symbol-keyed object pattern properties"

4. Run the affected package's existing tests, then the repository lint and type checks before requesting review.

Audit provenance

• Audit base: c9b56ab507f224426ee8388dc450da447ec4715f
• Reproduction base: c9b56ab507f224426ee8388dc450da447ec4715f
• Findings: core-g-r-match-symbol-key-pattern-omitted
• Initial patch: focused reproduction tests; implementation fix pending

[changeset-bot]

⚠️ No Changeset found

Latest commit: 20bb27d

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

This PR includes no changesets

When changesets are added to this PR, you'll see the packages that this PR includes changesets for and the associated semver types

Click here to learn what changesets are, and how to add one.

Click here if you're a maintainer who wants to add a changeset to this PR

[pullfrog]

Important

This PR reproduces the symbol-keyed object pattern bug with a focused regression test, but the implementation fix in packages/effect/src/internal/matcher.ts is still missing. CI will continue to fail until the fix is included.

Reviewed changes

• packages/effect/test/Match.test.ts: adds a regression test demonstrating that an object pattern with only a symbol key wrongly matches a value where the symbol property does not satisfy the constraint.

  ^{｜ ⚠️ this action is pinned to a commit SHA, which freezes the cleanup step — switch to @v0 or keep the SHA fresh with Dependabot ｜ Fix all ➔ ｜ Fix 👍s ➔ ｜ View workflow run ｜ Using Kimi K2 (free via Pullfrog for OSS) ｜ 𝕏}

[pullfrog]

The test only exercises the wrong-value path. Consider also asserting that { [key]: "expected" } matches ("hit") and that {} returns "miss", matching the hit/miss coverage of the neighboring tests and reducing the chance that an incomplete fix passes accidentally.