Fix stack overflow during subscript inference on recursive type aliases - #4635
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kavix wants to merge 1 commit into
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Fix stack overflow during subscript inference on recursive type aliases#4635kavix wants to merge 1 commit into
kavix wants to merge 1 commit into
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Recursive type aliases involved in nested mapping patterns (such as pattern matching on nested dictionary structures) could trigger recursive subscript inferences without termination, causing a stack overflow. Track active type aliases during subscript inference using a cycle-detection set. When an alias is encountered again on the active subscript path, terminate recursion by returning an implicit Any type.
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This pull request has been imported. If you are a Meta employee, you can view this in D117121160. (Because this pull request was imported automatically, there will not be any future comments.) |
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According to mypy_primer, this change doesn't affect type check results on a corpus of open source code. ✅ |
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Summary
Fixes #4631.
Nested mapping-pattern inference re-entered subscript inference through recursive
UntypedAliasvalues. Each expansion recreated the alias-containing type, causing unbounded recursion and a native stack overflow crash.Changes
subscript_infer_for_type_with_key_presentto maintain an activeSmallSet<TypeAliasData>.Any.test_recursive_alias_mapping_pattern_does_not_overflowinpyrefly/lib/test/pattern_match.rs.Test Plan
cargo test pattern_match(verified all 98 tests pass)cargo test test_recursive_alias_mapping_pattern_does_not_overflow -- --nocapturepython3 test.py --no-test --no-tensor-shapes --no-conformance --no-jsonschema