Issue with itemgetter, SupportsGetItem and min

[Avasam]

Bug Report
Sorry for the vague title. I'm not sure whether this is a bug or if I'm doing something wrong. This came up in python/typeshed#9117 . Pyright reports no error with the usage of itemgetter here. And both type-checkers reveal the right type returned from min in this example.

To Reproduce

from _typeshed import SupportsDunderGT, SupportsDunderLT
from collections.abc import Callable
from typing import Any, Generic, Protocol, Tuple, TypeVar, Union
from typing_extensions import final

_T = TypeVar("_T")
_T_contra = TypeVar("_T_contra", contravariant=True)
_T_co = TypeVar("_T_co", covariant=True)
_VT_co = TypeVar("_VT_co", covariant=True)
_KT_contra = TypeVar("_KT_contra", contravariant=True)

# Simplified from typeshed
class SupportsGetItem(Protocol[_KT_contra, _VT_co]):
 def __contains__(self, __x: Any) -> bool: ...
 def __getitem__(self, __key: _KT_contra) -> _VT_co: ...

# Simplified from typeshed, with the generic typing change to __call__
@final
class itemgetter(Generic[_T_co]):
 def __new__(cls, item: _T_co) -> itemgetter[_T_co]: ...
 def __call__(self, obj: SupportsGetItem[_T_co, _T]) -> _T: ...

# This is the same as itemgetter.__call__
def standalone_call(obj: SupportsGetItem[int, _T]) -> _T: ...

reveal_type(itemgetter(1).__call__)

test_dict = min({"first": 1, "second": 2}, key=itemgetter(1))
test_items = min({"first": 1, "second": 2}.items(), key=itemgetter(1)) # mypy error
test_dict_standalone = min({"first": 1, "second": 2}, key=standalone_call)
test_items_standalone = min({"first": 1, "second": 2}.items(), key=standalone_call) # mypy error

reveal_type(test_dict)
reveal_type(test_items)

expected_type_form_min_param_1: Callable[[Tuple[str, int]], Union[SupportsDunderLT[Any], SupportsDunderGT[Any]]]
revealed_type_itemgetter_call: Callable[[SupportsGetItem[Any, _T]], _T] # pyright error

revealed_type_itemgetter_call = itemgetter(1)
expected_type_form_min_param_1 = itemgetter(1) # mypy error

revealed_type_itemgetter_call = standalone_call
expected_type_form_min_param_1 = standalone_call # mypy error

Expected Behavior

No error? Maybe?

Actual Behavior

(.venv) PS C:\Users\Avasam\Desktop> mypy .\operator_reveal_type.pyi
operator_reveal_type.pyi:26: note: Revealed type is "def [_T] (obj: operator_reveal_type.SupportsGetItem[Any, _T`3]) -> _T`3"
operator_reveal_type.pyi:29: error: Argument "key" to "min" has incompatible type "itemgetter[int]"; expected "Callable[[Tuple[str, int]], Union[SupportsDunderLT[Any], SupportsDunderGT[Any]]]" 
[arg-type]
operator_reveal_type.pyi:29: note: "itemgetter[int].__call__" has type "Callable[[Arg(SupportsGetItem[Any, _T], 'obj')], _T]"
operator_reveal_type.pyi:31: error: Argument "key" to "min" has incompatible type "Callable[[SupportsGetItem[Any, _T]], _T]"; expected "Callable[[Tuple[str, int]], Union[SupportsDunderLT[Any], SupportsDunderGT[Any]]]" [arg-type]
operator_reveal_type.pyi:33: note: Revealed type is "builtins.str"
operator_reveal_type.pyi:34: note: Revealed type is "Tuple[builtins.str, builtins.int]"
operator_reveal_type.pyi:40: error: Incompatible types in assignment (expression has type "itemgetter[int]", variable has type "Callable[[Tuple[str, int]], Union[SupportsDunderLT[Any], SupportsDunderGT[Any]]]") [assignment]
operator_reveal_type.pyi:40: note: "itemgetter[int].__call__" has type "Callable[[Arg(SupportsGetItem[Any, _T], 'obj')], _T]"
operator_reveal_type.pyi:43: error: Incompatible types in assignment (expression has type "Callable[[SupportsGetItem[Any, _T]], _T]", variable has type "Callable[[Tuple[str, int]], Union[SupportsDunderLT[Any], SupportsDunderGT[Any]]]") [assignment]
Found 4 errors in 1 file (checked 1 source file)

Your Environment

• Mypy version used: 0.982 AND 0.990 (compiled: yes)
• Mypy command-line flags: N/A
• Mypy configuration options from mypy.ini (and other config files): N/A
• Python version used: 3.9.13

[ilevkivskyi]

TBH it is hard to follow as the example is complicated, but it typechecks without errors on current master.

[Avasam]

I just tested and it's been fixed in mypy 1.11.0