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Reject recursive aliases that grow through Concatenate #22032

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Reject recursive aliases that grow through Concatenate #22032

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1 change: 1 addition & 0 deletions mypy/typeanal.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2523,6 +2523,7 @@ def visit_type_alias_type(self, t: TypeAliasType) -> Type:
for arg in t.args:
if not (
isinstance(arg, TypeVarLikeType)
and not (isinstance(arg, ParamSpecType) and arg.prefix.arg_types)
or isinstance(arg, UnpackType)
and isinstance(arg.type, TypeVarLikeType)
) and has_type_vars(arg):
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13 changes: 13 additions & 0 deletions test-data/unit/check-python312.test
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Original file line number Diff line number Diff line change
Expand Up @@ -2373,3 +2373,16 @@ if TYPE_CHECKING:
class Group(TypedDict):
params: "Tuple[Alias, ...]"
[builtins fixtures/tuple.pyi]

[case testPEP695TypeAliasRecursiveConcatenateNoCrash]
from typing import Callable
from typing_extensions import Concatenate

type A[**P] = Callable[[Callable[P, None]], A[Concatenate[int, P]]] # E: Invalid recursive alias: type variable nesting on right hand side
type B[**P] = Callable[[Callable[P, None]], B[P]]

def foo[**P](a: A[P], b: B[P]) -> None:
reveal_type(a) # N: Revealed type is "Any"
reveal_type(b) # N: Revealed type is "def (def (*P.args, **P.kwargs)) -> ..."
[builtins fixtures/tuple.pyi]
[typing fixtures/typing-full.pyi]
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