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Fix nondeterministic type checking by making join between TypeType and TypeVar commute #19149

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Merged
merged 1 commit into from
May 27, 2025
Merged

Fix nondeterministic type checking by making join between TypeType and TypeVar commute #19149

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2 changes: 2 additions & 0 deletions mypy/join.py
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Original file line number Diff line number Diff line change
Expand Up @@ -635,6 +635,8 @@ def default(self, typ: Type) -> ProperType:
typ = get_proper_type(typ)
if isinstance(typ, Instance):
return object_from_instance(typ)
elif isinstance(typ, TypeType):
return self.default(typ.item)
elif isinstance(typ, UnboundType):
return AnyType(TypeOfAny.special_form)
elif isinstance(typ, TupleType):
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4 changes: 4 additions & 0 deletions mypy/test/testtypes.py
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Expand Up @@ -1064,6 +1064,10 @@ def test_variadic_tuple_joins(self) -> None:
self.tuple(UnpackType(Instance(self.fx.std_tuplei, [self.fx.a])), self.fx.a),
)

def test_join_type_type_type_var(self) -> None:
self.assert_join(self.fx.type_a, self.fx.t, self.fx.o)
self.assert_join(self.fx.t, self.fx.type_a, self.fx.o)

# There are additional test cases in check-inference.test.

# TODO: Function types + varargs and default args.
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