No warning for instantiating abstract class in function

[Holt59]

• Are you reporting a bug, or opening a feature request?

BUG

• Please insert below the code you are checking with mypy,

import abc

class A(abc.ABC):
    @abc.abstractmethod
    def f(self): pass

# Cannot instantiate abstract class 'A' with abstract attribute 'f'
a = A()

# Cannot instantiate abstract class 'A' with abstract attribute 'f'
al = lambda: A()

# No warnings
def af():
    return A()

https://mypy-play.net/?mypy=latest&python=3.8&gist=fbc0513ec90bda028634ade70ff698e2

• What is the actual behavior/output?

See comments above.

• What is the behavior/output you expect?

I expect the "Cannot instantiate abstract class [...]" warning in all three cases.

[Akuli]

You need to add type hints to af to make mypy check it:

def af() -> A:
    return A()   # error

This behaviour is documented: https://mypy.readthedocs.io/en/stable/common_issues.html#no-errors-reported-for-obviously-wrong-code