[Regression] field(default_factory=set) is miscompiled

[JelleZijlstra]

Given this code:

from dataclasses import dataclass, field
from typing import Set


@dataclass
class X:
    s: Set[str] = field(default_factory=set)

Compiling with mypyc setfield.py on 0.931 and then running import setfield fails with:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "setfield.py", line 7, in <module>
    s: Set[str] = field(default_factory=set)
KeyError: 'set'

On 0.920 it works as expected.

Inspecting the C and the IR (thanks @ichard26) shows that we're incorrectly looking up set in the module globals instead of the builtins.

L20:
    r59 = load_address PyType_Type
    r60 = test.globals :: static
    r61 = 'set'
    r62 = CPyDict_GetItem(r60, r61)
    if is_error(r62) goto L36 (error at <module>:7) else goto L21

[ichard26]

Bisected to python/mypy@1bcfc04 by the way.

[hauntsaninja]

cc @chadrik if you have time to take a look :-)