Fixes python#12109. The original issue reported that the bug had to do with the use of the `--follow-imports=skip` flag. However, it turned out this was a red herring after closer inspection: I was able to trigger a more minimal repro both with and without this flag: ```python from enum import Enum class Foo(Enum): a = [] # E: Need type annotation for "a" (hint: "a: List[<type>] = ...") b = None def check(self) -> None: reveal_type(Foo.a.value) # N: Revealed type is "<partial list[?]>" reveal_type(Foo.b.value) # N: Revealed type is "<partial None>" ``` The first two `reveal_types` demonstrate the crux of the bug: the enum plugin does not correctly handle and convert partial types into regular types when inferring the type of the `.value` field. This can then cause any number of downstream problems. For example, suppose we modify `def check(...)` so it runs `reveal_type(self.value)`. Doing this will trigger a crash in mypy because it makes the enum plugin eventually try running `is_equivalent(...)` on the two partial types. But `is_equivalent` does not support partial types, so we crash. I opted to solve this problem by: 1. Making the enum plugin explicitly call the `fixup_partial_types` function on all field types. This prevents the code from crashing. 2. Modifies mypy so that Final vars are never marked as being PartialTypes. Without this, `reveal_type(Foo.b.value)` would report a type of `Union[Any, None]` instead of just `None`. (Note that all enum fields are implicitly final).

Commits

Commits on Nov 6, 2022

Fix crash with PartialTypes and the enum plugin