[red-knot] is_subtype_of fix for KnownInstance types#14750
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`KnownInstance::instance_fallback` may return instances of supertypes. For example, it returns an instance of `_SpecialForm` for `Literal`. This means it can't be used on the right-hand side of `is_subtype_of` relationships, because it might lead to false positives. I can lead to false negatives on the left hand side of `is_subtype_of`, but this is at least a known limitation. False negatives are fine for most applications, but false positives can lead to wrong results in intersection-simplification, for example.
sharkdp
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carljm
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AlexWaygood
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Dec 3, 2024
dcreager
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Dec 3, 2024
* main: [`ruff`] Extend unnecessary-regular-expression to non-literal strings (`RUF055`) (#14679) Minor followups to RUF052 (#14755) [red-knot] Property tests (#14178) [red-knot] `is_subtype_of` fix for `KnownInstance` types (#14750) Improve docs for flake8-use-pathlib rules (#14741) [`ruff`] Implemented `used-dummy-variable` (`RUF052`) (#14611) [red-knot] Simplify tuples containing `Never` (#14744) Possible fix for flaky file watching test (#14543) [`flake8-import-conventions`] Improve syntax check for aliases supplied in configuration for `unconventional-import-alias (ICN001)` (#14745) [red-knot] Deeper understanding of `LiteralString` (#14649) red-knot: support narrowing for bool(E) (#14668) [`refurb`] Handle non-finite decimals in `verbose-decimal-constructor (FURB157)` (#14596) [red-knot] Re-enable linter corpus tests (#14736)
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Summary
KnownInstance::instance_fallbackmay return instances of supertypes. For example, it returns an instance of_SpecialFormforLiteral. This means it can't be used on the right-hand side ofis_subtype_ofrelationships, because it might lead to false positives.I can lead to false negatives on the left hand side of
is_subtype_of, but this is at least a known limitation. False negatives are fine for most applications, but false positives can lead to wrong results in intersection-simplification, for example.closes #14731
Test Plan
Added regression test