Oct 12, 2025 · Oct 10, 2025
diff --git a/mypy/meet.py b/mypy/meet.py
    ):
 # We put this branch early to get T(bound=Union[A, B]) instead of
 # Union[T(bound=A), T(bound=B)] that will be confusing for users.
 returndeclared.copy_modified(upper_bound=original_narrowed)
 returndeclared.copy_modified(
 upper_bound=narrow_declared_type(declared.upper_bound,original_narrowed)
        )
 elifnotis_overlapping_types(declared,narrowed,prohibit_none_typevar_overlap=True):
 ifstate.strict_optional:
 returnUninhabitedType()
diff --git a/test-data/unit/check-typeguard.test b/test-data/unit/check-typeguard.test
    return 0
 [builtins fixtures/tuple.pyi]

 [case testTypeGuardedTypeDoesNotLeakTypeVar]
 # flags: --debug-serialize
 # https://github.com/python/mypy/issues/20015
 from typing import Generic, TypeVar, TypeGuard

 class A: ...
 class B: ...

 def is_a(_: object) -> TypeGuard[A]: return True
 def is_b(_: object) -> TypeGuard[B]: return True

 _T = TypeVar("_T")

 class Foo(Generic[_T]):
    def __init__(self, v: _T) -> None:
        if is_a(v) or is_b(v):
            self.v = v
 [builtins fixtures/tuple.pyi]
 [typing fixtures/typing-full.pyi]

 [case testTypeGuardRestrictTypeVarUnion]
 from typing import Union, TypeVar
 from typing_extensions import TypeGuard
diff --git a/test-data/unit/fixtures/typing-full.pyi b/test-data/unit/fixtures/typing-full.pyi
 ClassVar = 0
 Final = 0
 TypedDict = 0
 TypeGuard = 0
 NoReturn = 0
 NewType = 0
 Self = 0
Original file line number	Diff line number	Diff line change
Expand Up		@@ -170,7 +170,9 @@ def narrow_declared_type(declared: Type, narrowed: Type) -> Type:
		):
		# We put this branch early to get T(bound=Union[A, B]) instead of
		# Union[T(bound=A), T(bound=B)] that will be confusing for users.
		returndeclared.copy_modified(upper_bound=original_narrowed)
		returndeclared.copy_modified(
		upper_bound=narrow_declared_type(declared.upper_bound,original_narrowed)
		)
		elifnotis_overlapping_types(declared,narrowed,prohibit_none_typevar_overlap=True):
		ifstate.strict_optional:
		returnUninhabitedType()
Expand Down
Original file line number	Diff line number	Diff line change
Expand Up		@@ -825,6 +825,26 @@ def handle(model: Model) -> int:
		return 0
		[builtins fixtures/tuple.pyi]

		[case testTypeGuardedTypeDoesNotLeakTypeVar]
		# flags: --debug-serialize
		# https://github.com/python/mypy/issues/20015
		from typing import Generic, TypeVar, TypeGuard

		class A: ...
		class B: ...

		def is_a(_: object) -> TypeGuard[A]: return True
		def is_b(_: object) -> TypeGuard[B]: return True

		_T = TypeVar("_T")

		class Foo(Generic[_T]):
		def __init__(self, v: _T) -> None:
		if is_a(v) or is_b(v):
		self.v = v
		[builtins fixtures/tuple.pyi]
		[typing fixtures/typing-full.pyi]

		[case testTypeGuardRestrictTypeVarUnion]
		from typing import Union, TypeVar
		from typing_extensions import TypeGuard
Expand Down