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7 changes: 3 additions & 4 deletions mypy/semanal.py
Original file line number Diff line number Diff line change
Expand Up @@ -1791,11 +1791,10 @@ def push_type_args(
return None
tvs.append((p.name, tv))

for name, tv in tvs:
if self.is_defined_type_param(name):
self.fail(f'"{name}" already defined as a type parameter', context)
if self.is_defined_type_param(p.name):
self.fail(f'"{p.name}" already defined as a type parameter', context)
else:
self.add_symbol(name, tv, context, no_progress=True, type_param=True)
self.add_symbol(p.name, tv, context, no_progress=True, type_param=True)

return tvs

Expand Down
29 changes: 29 additions & 0 deletions test-data/unit/check-python313.test
Original file line number Diff line number Diff line change
Expand Up @@ -290,3 +290,32 @@ reveal_type(A1().x) # N: Revealed type is "builtins.int"
reveal_type(A2().x) # N: Revealed type is "builtins.int"
reveal_type(A3().x) # N: Revealed type is "builtins.int"
[builtins fixtures/tuple.pyi]

[case testTypeVarDefaultToAnotherTypeVar]
class A[X, Y = X, Z = Y]:
x: X
y: Y
z: Z

a1: A[int]
reveal_type(a1.x) # N: Revealed type is "builtins.int"
reveal_type(a1.y) # N: Revealed type is "builtins.int"
# TODO: this must reveal `int` as well:
reveal_type(a1.z) # N: Revealed type is "X`1"

a2: A[int, str]
reveal_type(a2.x) # N: Revealed type is "builtins.int"
reveal_type(a2.y) # N: Revealed type is "builtins.str"
reveal_type(a2.z) # N: Revealed type is "builtins.str"

a3: A[int, str, bool]
reveal_type(a3.x) # N: Revealed type is "builtins.int"
reveal_type(a3.y) # N: Revealed type is "builtins.str"
reveal_type(a3.z) # N: Revealed type is "builtins.bool"
[builtins fixtures/tuple.pyi]

[case testTypeVarDefaultToAnotherTypeVarWrong]
class A[Y = X, X = int]: ... # E: Name "X" is not defined

class B[Y = X]: ... # E: Name "X" is not defined
[builtins fixtures/tuple.pyi]