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brianschubertbrianschubert
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Disallow TypeVar constraints parameterized by type variables (#18186)
Emit an error for [this test case](https://github.com/python/typing/blob/46b05a4c10ed3841c9bc5126ba9f31dd8ae061e7/conformance/tests/generics_basic.py#L54-L55) from the conformance tests: ```python class Test(Generic[T]): BadConstraint2 = TypeVar("BadConstraint2", str, list[T]) # E ```
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+55
-3
lines changed

4 files changed

+55
-3
lines changed

‎mypy/message_registry.py

Lines changed: 4 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -350,6 +350,10 @@ def with_additional_msg(self, info: str) -> ErrorMessage:
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"Await expression cannot be used as a type variable bound", codes.SYNTAX
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)
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353+
TYPE_VAR_GENERIC_CONSTRAINT_TYPE: Final = ErrorMessage(
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"TypeVar constraint type cannot be parametrized by type variables", codes.MISC
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)
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TYPE_ALIAS_WITH_YIELD_EXPRESSION: Final = ErrorMessage(
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"Yield expression cannot be used within a type alias", codes.SYNTAX
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)

‎mypy/semanal.py

Lines changed: 12 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -290,6 +290,7 @@
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UnpackType,
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get_proper_type,
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get_proper_types,
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has_type_vars,
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is_named_instance,
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remove_dups,
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type_vars_as_args,
@@ -1856,13 +1857,17 @@ def analyze_type_param(
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else:
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default = AnyType(TypeOfAny.from_omitted_generics)
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if type_param.kind == TYPE_VAR_KIND:
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values = []
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values: list[Type] = []
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if type_param.values:
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for value in type_param.values:
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analyzed = self.anal_type(value, allow_placeholder=True)
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if analyzed is None:
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analyzed = PlaceholderType(None, [], context.line)
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values.append(analyzed)
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if has_type_vars(analyzed):
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self.fail(message_registry.TYPE_VAR_GENERIC_CONSTRAINT_TYPE, context)
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values.append(AnyType(TypeOfAny.from_error))
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else:
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values.append(analyzed)
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return TypeVarExpr(
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name=type_param.name,
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fullname=fullname,
@@ -5044,7 +5049,11 @@ def analyze_value_types(self, items: list[Expression]) -> list[Type]:
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# soon, even if some value is not ready yet, see process_typevar_parameters()
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# for an example.
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analyzed = PlaceholderType(None, [], node.line)
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result.append(analyzed)
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if has_type_vars(analyzed):
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self.fail(message_registry.TYPE_VAR_GENERIC_CONSTRAINT_TYPE, node)
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result.append(AnyType(TypeOfAny.from_error))
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else:
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result.append(analyzed)
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except TypeTranslationError:
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self.fail("Type expected", node)
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result.append(AnyType(TypeOfAny.from_error))

‎test-data/unit/check-python312.test

Lines changed: 23 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1525,6 +1525,29 @@ reveal_type(E[str]().a) # N: Revealed type is "builtins.list[Any]"
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[builtins fixtures/type.pyi]
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[typing fixtures/typing-full.pyi]
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[case testPEP695TypeAliasInvalidGenericConstraint]
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class A[T]:
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class a[S: (int, list[T])]: pass # E: Name "T" is not defined
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type b[S: (int, list[T])] = S # E: TypeVar constraint type cannot be parametrized by type variables
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def c[S: (int, list[T])](self) -> None: ... # E: TypeVar constraint type cannot be parametrized by type variables
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[builtins fixtures/tuple.pyi]
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[typing fixtures/typing-full.pyi]
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[case testPEP695TypeAliasUnboundTypeVarConstraint]
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from typing import TypeVar
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T = TypeVar("T")
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class a[S: (int, list[T])]: pass # E: Type variable "__main__.T" is unbound \
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# N: (Hint: Use "Generic[T]" or "Protocol[T]" base class to bind "T" inside a class) \
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# N: (Hint: Use "T" in function signature to bind "T" inside a function)
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type b[S: (int, list[T])] = S # E: Type variable "__main__.T" is unbound \
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# N: (Hint: Use "Generic[T]" or "Protocol[T]" base class to bind "T" inside a class) \
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# N: (Hint: Use "T" in function signature to bind "T" inside a function)
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def c[S: (int, list[T])](self) -> None: ... # E: Type variable "__main__.T" is unbound \
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# N: (Hint: Use "Generic[T]" or "Protocol[T]" base class to bind "T" inside a class) \
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# N: (Hint: Use "T" in function signature to bind "T" inside a function)
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[builtins fixtures/tuple.pyi]
1549+
[typing fixtures/typing-full.pyi]
1550+
15281551
[case testPEP695RedefineAsTypeAlias1]
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class C: pass
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type C = int # E: Name "C" already defined on line 1

‎test-data/unit/semanal-errors.test

Lines changed: 16 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1060,6 +1060,22 @@ S = TypeVar('S', covariant=True, contravariant=True) \
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# E: TypeVar cannot be both covariant and contravariant
10611061
[builtins fixtures/bool.pyi]
10621062

1063+
[case testInvalidTypevarArgumentsGenericConstraint]
1064+
from typing import Generic, List, TypeVar
1065+
from typing_extensions import Self
1066+
1067+
T = TypeVar("T")
1068+
1069+
def f(x: T) -> None:
1070+
Bad = TypeVar("Bad", int, List[T]) # E: TypeVar constraint type cannot be parametrized by type variables
1071+
class C(Generic[T]):
1072+
Bad = TypeVar("Bad", int, List[T]) # E: TypeVar constraint type cannot be parametrized by type variables
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class D:
1074+
Bad = TypeVar("Bad", int, List[Self]) # E: TypeVar constraint type cannot be parametrized by type variables
1075+
S = TypeVar("S", int, List[T]) # E: Type variable "__main__.T" is unbound \
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# N: (Hint: Use "Generic[T]" or "Protocol[T]" base class to bind "T" inside a class) \
1077+
# N: (Hint: Use "T" in function signature to bind "T" inside a function)
1078+
10631079
[case testInvalidTypevarValues]
10641080
from typing import TypeVar
10651081
b = TypeVar('b', *[int]) # E: Unexpected argument to "TypeVar()"

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