Introduce a helper function to map types to protocols + fix for dict kwargs false positive #20419
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randolf-scholz
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Dec 16, 2025
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| from mypy.subtypes import is_subtype | ||
| from mypy.typeops import get_all_type_vars |
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had to put these there due to circular import issues
randolf-scholz
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Dec 16, 2025
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| # need to manually include these because solve_constraints ignores them | ||
| # apparently | ||
| constraints.append(Constraint(tvar, SUBTYPE_OF, tvar.upper_bound)) |
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Is it intentional that solve_constraints ignores the upper bounds of the tvars it solves for?
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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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Fixes: #20424
Following my comments in #20416, this PR introduces a new helper function
as_typethat can be used to determine whether a type can be matched to a certain protocol or not.As an example application, I fix a bug in
is_valid_keyword_var_argthat stems from checkingkwargs <: SupportsKeyAndGetItem[str, Any]This check is too eager, because
SupportsKeyAndGetItemis invariant in the key type, it will produce a false positive whenkwargsis for instancedict[Literal["foo", "bar"], int]. The correct test is:Does there exist
T <: strso thatkwargs <: SupportsKeyAndGetItem[T, Any]which can be checked with the new helper function.
Updated tests
I updated
testLiteralKwargsto test:dictargumentMappingargumentSupportsKeyAndGetitemargument