fix: do not treat empty arrays as universal match#14
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object::match used subset.empty() for both {} and [], so empty-array
candidates made {"$in":[[]]} match any value and {"tags":[]} match any
tags. Restrict the wildcard to empty objects; arrays keep same-length
equality.
Co-authored-by: Kaius Ruokonen <ruoka@users.noreply.github.com>
$in/$nin only apply on primitive match paths; empty-array LHS never enters that branch. Keep the primitive and field-equality regressions. Co-authored-by: Kaius Ruokonen <ruoka@users.noreply.github.com>
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July 20, 2026 21:31
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Jul 21, 2026
* fix: do not treat empty arrays as universal match
object::match used subset.empty() for both {} and [], so empty-array
candidates made {"$in":[[]]} match any value and {"tags":[]} match any
tags. Restrict the wildcard to empty objects; arrays keep same-length
equality.
Co-authored-by: Kaius Ruokonen <ruoka@users.noreply.github.com>
* test: drop invalid $in assertions on array LHS
$in/$nin only apply on primitive match paths; empty-array LHS never
enters that branch. Keep the primitive and field-equality regressions.
Co-authored-by: Kaius Ruokonen <ruoka@users.noreply.github.com>
---------
Co-authored-by: Cursor Agent <cursoragent@cursor.com>
Co-authored-by: Kaius Ruokonen <ruoka@users.noreply.github.com>
This was referenced Jul 21, 2026
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Bug and impact
object::matchtreated any empty subset as a universal match viasubset.empty(). Empty arrays are empty too, so:{"$in":[[]]}matched any primitive value{"$nin":[[]]}matched no values{"tags":[]}matched anytagsvalueQuery filters could silently match all (or none) of the intended documents.
Root cause
The early return
if (subset.empty()) return trueis correct for Mongo-style empty object queries ({}), but array matching is same-length equality and$in/$ninreusematch()for candidates. Empty arrays must not share the object wildcard.Fix
Restrict the wildcard to empty objects:
subset.has_objects() && subset.empty(). Empty arrays fall through to the existing array equality path (or mismatch → false).Validation
MatchArrayand added$in/$nin/field-equality regressions inMatchInNinAcceptArrayOperand../tools/CB.sh debug test --tags='\[xson\]'— 410/410 passed.Also noted
PR #13 (FSON object name/value pairing) remains open and is a separate issue.