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Fix crash on Unpack used without arguments in class bases #21470

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ilevkivskyi merged 1 commit into from
May 12, 2026
+11 −0
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Fix crash on Unpack used without arguments in class bases #21470

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3 changes: 3 additions & 0 deletions mypy/semanal.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2403,6 +2403,9 @@ def analyze_unbound_tvar(self, t: Type) -> tuple[str, TypeVarLikeExpr] | None:
if isinstance(t, UnboundType):
sym = self.lookup_qualified(t.name, t)
if sym and sym.fullname in UNPACK_TYPE_NAMES:
if not t.args:
# Unpack used without arguments, e.g. `Protocol[Unpack]`
return None
inner_t = t.args[0]
if isinstance(inner_t, UnboundType):
return self.analyze_unbound_tvar_impl(inner_t, is_unpacked=True)
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8 changes: 8 additions & 0 deletions test-data/unit/check-typevar-tuple.test
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Expand Up @@ -2765,3 +2765,11 @@ def func(d: Callable[[Unpack[Ts]], T]) -> T: ...
y = func[1, int] # E: Type application is only supported for generic classes \
# E: Invalid type: try using Literal[1] instead?
[builtins fixtures/tuple.pyi]

[case testTypeVarTupleUnpackWithoutArgsInProtocol]
# https://github.com/python/mypy/issues/21467
from typing import Protocol, Unpack

class C(Protocol[Unpack]): # E: Free type variable expected in Protocol[...]
pass
[builtins fixtures/tuple.pyi]
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