Segfault / RecursionError when calling an instance whose class declares __call__ as an attribute of its own type #22361

Crash Report

mypy crashes when an instance is called and its class declares __call__ as an attribute annotated with the class itself, a Self union, or C | None. Declaring the class is fine. The crash happens on the call expression. Compiled wheels segfault, and a pure-Python build raises RecursionError.

Possibly related to the closed callable-protocol-with-Self crashes (#17314, #16877), though those used protocols with a __call__ method.

Traceback

On master (pure Python):

case.py:5: error: INTERNAL ERROR -- Please try using mypy master on GitHub:
...
  File ".../mypy/expandtype.py", line 654, in expand_self_type
    return expand_type(typ, {var.info.self_type.id: replacement})
  File ".../mypy/expandtype.py", line 74, in expand_type
    return typ.accept(ExpandTypeVisitor(env, normalize_callables))
RecursionError: maximum recursion depth exceeded

Compiled wheels (2.4.0, 2.4.1) print no traceback and exit with Segmentation fault (exit code 139).

To Reproduce

class C:
    __call__: "C"

def f(x: C) -> None:
    x()

Run: mypy --python-version 3.13 --no-incremental case.py

Also crashes with __call__: "C | None", and with from typing import Self plus __call__: Self | None.

mypy-play: https://mypy-play.net/?gist=e7b53eb68b638455a3bac9a39f9f0a79

Expected Behavior

No crash. Either an error about the call or accepting it would be better than a crash.

Your Environment

• Mypy version used: 2.4.0, 2.4.1 (compiled, segfault) and master 2.5.0+dev.623bef9 (RecursionError)

• Mypy command-line flags: --python-version 3.13 --no-incremental

• Mypy configuration options from mypy.ini (and other config files): none

• Python version used: 3.13.16

• Operating system and version: Linux