mypy sometimes ignores type errors inside calls to overloaded functions

[msullivan]

In the following program:

from typing import Union, Iterable, Tuple

class A:
    def foo(self) -> Iterable[Tuple[int, int]]: pass

def bar(x: int) -> Union[A, int]: ...

list(bar('lol').foo())  # No errors!
dict(bar('lol').foo())  # No errors!

tuple(bar('lol').foo())  # Does error
set(bar('lol').foo())  # Does error

two errors ought to be generated for each call (one for int not having .foo, one for 'lol' being the wrong type of argument). These errors seem to be suppressed while checking list and dict, which get filled with Anys.

[msullivan]

This looks like an overloads issue. The following doesn't produce any errors:

from typing import Union, Iterable, Tuple, TypeVar, Generic, overload, Any

class A:
    def foo(self) -> Iterable[Tuple[int, int]]: pass

def bar(x: int) -> Union[A, int]: ...

_T = TypeVar('_T')

@overload
def foo() -> None: ...
@overload
def foo(iterable: Iterable[_T]) -> None: ...

def foo(iterable: Any = None) -> None: pass

foo(bar('lol').foo())  # No errors!

This is a regression from 0.610 to 0.620 (I haven't dug any deeper than that.)

@Michael0x2a thoughts?