Fix integer underflow in all_mutually_exclusive for empty subschemas - #1028
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An empty subschema list (e.g. from a degenerate "anyOf": []) caused `len - 1` to underflow: a panic in debug builds and an effectively unbounded iteration in release builds. Return true for fewer than two subschemas since mutual exclusivity is vacuously satisfied.
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ahl
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Aug 5, 2026
- reword and wrap comment in all_mutually_exclusive - remove redundant comment in test_all_mutually_exclusive_empty - s/uninhabited/unsatisfiable/
ahl
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Sep 9, 2026
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Problem
all_mutually_exclusiveintypify-impl/src/util.rscomputes(0..len - 1)over the subschema list. When the list is empty,len - 1underflows: this panics in debug builds and, in release builds, wraps tousize::MAXso the pair iteration effectively hangs. This is reachable from a degenerate but parseable input schema containing"anyOf": [], viaconvert_any_of.Fix
Guard at the top of the function: with fewer than two subschemas there are no pairs to compare, so mutual exclusivity is vacuously true (this preserves the existing behavior for a single subschema, which also produced no pairs). Added a unit test for the empty slice and a conversion-level test that an
"anyOf": []schema converts without panicking.Trade-offs
An empty
anyOfis arguably invalid input, so an alternative would be to reject it with an error during conversion. This change keeps the current behavior (the pipeline already handles it downstream) and only removes the underflow.