Callable vs Protocol with `self` argument

[Mercerenies]

Bug Report

mypy seems to be unwilling to bind self to a decorated method if the method's return type is declared as a Protocol with __call__, but is willing to do so if the return type is Callable. See the example below.

To Reproduce

https://mypy-play.net/?gist=2fb651ddee58d4176237eb3c3dfb7c1a

Expected Behavior

I expect no type errors in any of the examples provided.

Actual Behavior

The first example (with class A and Callable) is accepted. The second is not.

decorator_confusion.py:45: error: Too few arguments for "__call__" of "MyCallable"  [call-arg]

Your Environment

Tested on mypy 1.18.2 and 2.1.0. Python version 3.14.5

[beanscg]

I checked the member-binding path. Method-like attributes are bound in mypy/checkmember.py: analyze_var detects callable class-initialized vars and routes through expand_and_bind_callable (890-918), then expand_and_bind_callable applies check_self_arg and bind_self (962-978). check_self_arg also has a special case for __call__ when the self argument is a CallableType (1100-1104).

That makes the issue's difference between Callable and a Protocol-with-__call__ look like a structural-callable binding gap: the Callable return gets the expected method/self binding, while the protocol form still reports too few arguments for __call__.

A regression can keep the issue's two decorator cases side-by-side: return type Callable[..., ...] and return type Protocol defining __call__. Both should bind self consistently and avoid the Too few arguments for "__call__" error.