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Fix types of inherited attributes in generic dataclasses #12656

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merged 4 commits into from Apr 25, 2022

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JukkaL
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@JukkaL JukkaL commented Apr 22, 2022

Fixes #12633.

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@JukkaL JukkaL commented Apr 22, 2022

mypy_primer found some regressions.

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@JukkaL JukkaL commented Apr 22, 2022

The issue is that we are performing type operations during semantic analysis, when not everything may be correctly set up. We'll need to move any type operations to a later phase. We should probably have an assertion that gets triggered if trying to perform type operations when it's not okay to do so. This would save a lot of debugging.

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@cdce8p cdce8p commented Apr 23, 2022

mypy_primer found some regressions.

Isolated the regression with Home Assistant. Hope that helps.

from __future__ import annotations
from dataclasses import dataclass
from typing import Generic, TypeVar

T = TypeVar("T")

@dataclass
class Parent2(Generic[T]):
    key: str | None = None

@dataclass
class Child2(Parent2[T]): ...


Child2(key=None)  # <-- error
error: Argument "key" to "Child2" has incompatible type "None"; expected "str"

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@github-actions github-actions bot commented Apr 25, 2022

According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉

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@cdce8p cdce8p commented Apr 25, 2022

The last change does resolve all dataclass regressions I saw with Home Assistant.

A bit unfortunate that mypy_primer didn't found them earlier but I think it might be because it doesn't install project dependencies.

jhance
jhance approved these changes Apr 25, 2022
@JukkaL JukkaL merged commit cb6581a into master Apr 25, 2022
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@JukkaL JukkaL deleted the fix-dataclass-regression branch Apr 25, 2022
JukkaL added a commit that referenced this issue May 13, 2022
Move the attrs plugin to a later pass, so that we won't have placeholders. Fix
various issues related to forward references and generic inheritance, including
some crashes.

This is follow-up to #12762 and related to #12656 and #12633.
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3 participants