Subscripted generic classes should not be considered instances of type #116
Description
Summary
ty currently emits no error on the following code, but it should:
class Foo[T]: ...
def requires_type(x: type): ...
requires_type(Foo[int])Foo[int] here is not an instance of type. In the long run, it'll be quite important for us to understand this, as the runtime frequently distinguishes between generic aliases and instances of types:
REPL session demonstrating several places where generic aliases are not accepted as instances of `type`
Python 3.13.1 (main, Jan 3 2025, 12:04:03) [Clang 15.0.0 (clang-1500.3.9.4)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> class Foo[T]: ...
...
>>> isinstance(object(), Foo[int])
Traceback (most recent call last):
File "<python-input-1>", line 1, in <module>
isinstance(object(), Foo[int])
~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^
File "/Users/alexw/.pyenv/versions/3.13.1/lib/python3.13/typing.py", line 1375, in __instancecheck__
return self.__subclasscheck__(type(obj))
~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^
File "/Users/alexw/.pyenv/versions/3.13.1/lib/python3.13/typing.py", line 1378, in __subclasscheck__
raise TypeError("Subscripted generics cannot be used with"
" class and instance checks")
TypeError: Subscripted generics cannot be used with class and instance checks
>>> issubclass(object, Foo[int])
Traceback (most recent call last):
File "<python-input-2>", line 1, in <module>
issubclass(object, Foo[int])
~~~~~~~~~~^^^^^^^^^^^^^^^^^^
File "/Users/alexw/.pyenv/versions/3.13.1/lib/python3.13/typing.py", line 1378, in __subclasscheck__
raise TypeError("Subscripted generics cannot be used with"
" class and instance checks")
TypeError: Subscripted generics cannot be used with class and instance checks
>>> from functools import singledispatch
>>> @singledispatch
... def f(arg): ...
...
>>> @f.register(list[int])
... def f(arg): ...
...
Traceback (most recent call last):
File "<python-input-5>", line 1, in <module>
@f.register(list[int])
~~~~~~~~~~^^^^^^^^^^^
File "/Users/alexw/.pyenv/versions/3.13.1/lib/python3.13/functools.py", line 893, in register
raise TypeError(
...<3 lines>...
)
TypeError: Invalid first argument to `register()`: list[int]. Use either `@register(some_class)` or plain `@register` on an annotated function.This bug can also be seen in that both these assertions currently pass, when they should fail:
from ty_extensions import static_assert, is_subtype_of, is_assignable_to, TypeOf
class Foo[T]: ...
static_assert(is_subtype_of(TypeOf[Foo[int]], type))
static_assert(is_assignable_to(TypeOf[Foo[int]], type))https://play.ty.dev/d373a056-b58c-451b-a136-323e76970454
Cc. @dcreager for generics!