The following code (foo.pyi):

from typing import Any, Callable, overload

class T:
    def __getattr__(self, item: Any) -> T: ...

@overload
def f(f: Callable[..., Any], t: str = ...) -> Callable[...,  T]: ...
@overload
def f(f: str = ...) -> Callable[[Callable[..., Any]], Callable[..., T]]: ...

when used with current master

$ mypy --version                      
mypy 0.730+dev.aaad048cf6f88280f4295865882888b7721dacdb

with default options

mypy --show-traceback foo.py

results in RecursionError

Traceback (most recent call last):
  File "/home/zero323/anaconda3/bin/mypy", line 10, in <module>
    sys.exit(console_entry())
...
RecursionError: maximum recursion depth exceeded while calling a Python object
foo.pyi:6: : note: use --pdb to drop into pdb

with repeated following calls:

  File "/path/to/anaconda3/lib/python3.7/site-packages/mypy/subtypes.py", line 152, in _is_subtype
    ignore_promotions=self.ignore_promotions)
  File "/path/to/anaconda3/lib/python3.7/site-packages/mypy/subtypes.py", line 95, in is_subtype
    ignore_promotions=ignore_promotions))
  File "/path/to/anaconda3/lib/python3.7/site-packages/mypy/types.py", line 667, in accept
    return visitor.visit_instance(self)
  File "/path/to/anaconda3/lib/python3.7/site-packages/mypy/subtypes.py", line 232, in visit_instance

The problem disappears if:

• We remove __getattr__. Other dunders with the same signature, for example

  class T:
      def __getitem__(self, item: Any) -> T: ...
  

  seem to work fine.

• We change return type of __getattr__, for example:

  class T:
       def __getattr__(self, item: Any) -> str: ...
  

• We remove any of the overloaded f. Either

  def f(f: Callable[..., Any], t: str = ...) -> Callable[...,  T]: ...
  

  or

  def f(f: str = ...) -> Callable[[Callable[..., Any]], Callable[..., T]]: ...
  

  alone, works just fine.

• We change return type of the first overloaded f, for example to:

  def f(f: Callable[..., Any], t: str = ...) -> Callable[...,  int]: ...
  

  or even other Generic of T:

  def f(f: Callable[..., Any], t: str = ...) -> List[T]: ..
  

• We make t obligatory in both overloaded definitions, or remove it completely from the second one.

The same code causes segmentation fault with the latest PyPi release:

$ mypy --show-traceback foo.pyi
[1]    1530 segmentation fault  mypy --show-traceback foo.pyi

so it might be (?) related to #6579.