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Fix noncommutative joins with bounded TypeVars #20345

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Fix noncommutative joins with bounded TypeVars #20345

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47ebf8d
Fix noncommutative joins with bounded TypeVars
hauntsaninja Dec 1, 2025
6c6fa8f
test
hauntsaninja Dec 2, 2025
43a70bb
[pre-commit.ci] auto fixes from pre-commit.com hooks
pre-commit-ci[bot] Dec 2, 2025
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13 changes: 9 additions & 4 deletions mypy/join.py
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Original file line number Diff line number Diff line change
Expand Up @@ -297,10 +297,15 @@ def visit_erased_type(self, t: ErasedType) -> ProperType:
return self.s

def visit_type_var(self, t: TypeVarType) -> ProperType:
if isinstance(self.s, TypeVarType) and self.s.id == t.id:
if self.s.upper_bound == t.upper_bound:
return self.s
return self.s.copy_modified(upper_bound=join_types(self.s.upper_bound, t.upper_bound))
if isinstance(self.s, TypeVarType):
if self.s.id == t.id:
if self.s.upper_bound == t.upper_bound:
return self.s
return self.s.copy_modified(
upper_bound=join_types(self.s.upper_bound, t.upper_bound)
)
# Fix non-commutative joins
return get_proper_type(join_types(self.s.upper_bound, t.upper_bound))
else:
return self.default(self.s)

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