Fix integer underflow in all_mutually_exclusive for empty subschemas - #1028
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Fix integer underflow in all_mutually_exclusive for empty subschemas#1028danieleades wants to merge 1 commit into
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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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| subschemas: &'a [Schema], | ||
| ) -> Result<(TypeEntry, &'a Option<Box<Metadata>>)> { | ||
| // An empty `anyOf` cannot match any instance. | ||
| if subschemas.is_empty() { |
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I don't think an empty anyOf is a valid input for what it's worth.
Is this related to the fix?
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| // With fewer than two subschemas there are no pairs to compare, so the | ||
| // schemas are vacuously mutually exclusive. This also avoids underflow | ||
| // in `len - 1` below when `subschemas` is empty. |
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| // With fewer than two subschemas there are no pairs to compare, so the | |
| // schemas are vacuously mutually exclusive. This also avoids underflow | |
| // in `len - 1` below when `subschemas` is empty. | |
| // With fewer than two subschemas, this is a degenerate case where the lone schema is mutually exclusive with everything else (which happens to be nothing). |
And please line wrap
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| // An empty slice of subschemas has no pairs to compare, so it's | ||
| // vacuously true. This should not panic (previously `len - 1` | ||
| // underflowed for an empty slice). |
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| // An empty slice of subschemas has no pairs to compare, so it's | |
| // vacuously true. This should not panic (previously `len - 1` | |
| // underflowed for an empty slice). |
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| match &type_space.id_to_entry[&type_id].details { | ||
| super::TypeEntryDetails::Enum(details) => assert!(details.variants.is_empty()), | ||
| details => panic!("empty anyOf should be uninhabited, got {details:?}"), |
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I don't think "uninhabited" is a term we use typically. Usually something like "unsatisfiable"
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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.