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[ty] allow T: Never as subtype of Never (#18687)

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Felix Scherz 2025-06-16 19:46:17 +02:00 • committed by GitHub
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3 changed files with 10 additions and 6 deletions
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7
crates/ty_python_semantic/resources/mdtest/type_compendium/never.md
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@ -5,11 +5,11 @@
## `Never` is a subtype of every type
The `Never` type is the bottom type of Python's type system. It is a subtype of every type, but no
type is a subtype of `Never`, except for `Never` itself.
type is a subtype of `Never`, except for `Never` itself or type variables with upper bound `Never`.
```py
from ty_extensions import static_assert, is_subtype_of
from typing_extensions import Never
from typing_extensions import Never, TypeVar
class C: ...
@ -19,6 +19,9 @@ static_assert(is_subtype_of(Never, C))
static_assert(is_subtype_of(Never, Never))
static_assert(not is_subtype_of(int, Never))
T = TypeVar("T", bound=Never)
static_assert(is_subtype_of(T, Never))
```
## `Never` is assignable to every type

2
crates/ty_python_semantic/resources/mdtest/type_properties/materialization.md
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@ -337,8 +337,6 @@ def bounded_by_gradual[T: Any](t: T) -> None:
# Bottom materialization of `T: Any` is `T: Never`
static_assert(is_fully_static(TypeOf[bottom_materialization(T)]))
# TODO: This should not error, see https://github.com/astral-sh/ty/issues/638
# error: [static-assert-error]
static_assert(is_subtype_of(TypeOf[bottom_materialization(T)], Never))
def constrained_by_gradual[T: (int, Any)](t: T) -> None: