Incorrect (or absent) error message for DefaultDict

[ilevkivskyi]

With this code:

from typing import DefaultDict
from collections import defaultdict

d: DefaultDict[str, int]
d[1] = 2

mypy shows a strange error (note "dict" instead of "DefaultDict"):

error: Invalid index type "int" for "dict"; expected type "str"

Moreover, if I remove the (redundant) import from collections, then mypy passes without errors.

[ilevkivskyi]

Since it looks like this bug was introduced by my old PR, I will fix this. You could assign this issue to me (I can't do this myself).

[ilevkivskyi]

This was partially fixed by #3147, now the error message correctly mentions defaultdict[str, int] instead of just dict. However, still the message disappears if redundant collections import is removed.

[ilevkivskyi]

This is now fixed by python/typeshed#1456