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False positive of TCH003 on InitVar import #9666

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jonyscathe opened this issue Jan 29, 2024 · 5 comments · Fixed by #9688
Closed

False positive of TCH003 on InitVar import #9666

jonyscathe opened this issue Jan 29, 2024 · 5 comments · Fixed by #9688
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@charliermarsh
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@jonyscathe
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TCH003 should not be raised on InitVar or ClassVar import even if they are only used for typing within a dataclass.
This is because they are needed at runtime.

See the corresponding issue in flake8-type-checking for more information: snok/flake8-type-checking#83

Not sure if it should be fixed in the same way in ruff.

Currently using ruff==0.1.14

Settings:
[tool.ruff]
extend-select = ['D213']
ignore = ['ANN101', 'ANN401', 'D107', 'D203', 'D212', 'E203', 'ISC003', 'N803', 'N806', 'PLC1901', 'PLC2701']
line-length = 120
preview = true
select = ['ALL']
target-version = 'py312'

[tool.ruff.format]
line-ending = 'lf'
quote-style = 'single'

[tool.ruff.lint.flake8-implicit-str-concat]
allow-multiline = false

[tool.ruff.lint.flake8-quotes]
inline-quotes = 'single'

[tool.ruff.lint.flake8-type-checking]
strict = true

[tool.ruff.lint.isort]
known-first-party = ['namespace.project']

[tool.ruff.lint.pylint]
max-args = 8
@jonyscathe
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I now realise that the setting: exempt-modules = ["dataclasses"] does fix this.
So I guess that is fine. Not the most ideal solution as it could mask genuine issues, but it'll work.

@charliermarsh
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Is the right solution here not to add @dataclass to runtime-evaluated-decorators? See: https://docs.astral.sh/ruff/settings/#flake8-type-checking-runtime-evaluated-decorators.

@charliermarsh
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Oh, but I guess this only applies to InitVar specifically, and not other annotations used within dataclasses?

@charliermarsh charliermarsh added question Asking for support or clarification bug Something isn't working and removed question Asking for support or clarification labels Jan 29, 2024
@charliermarsh
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We can fix this.

@charliermarsh charliermarsh self-assigned this Jan 29, 2024
@charliermarsh charliermarsh mentioned this issue Jan 29, 2024
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charliermarsh added a commit that referenced this issue Jan 29, 2024
@charliermarsh
Avoid marking InitVar as a typing-only annotation (#9688)
11449ac 
## Summary

Given:

```python
from dataclasses import InitVar, dataclass

@DataClass
class C:
    i: int
    j: int = None
    database: InitVar[DatabaseType] = None

    def __post_init__(self, database):
        if self.j is None and database is not None:
            self.j = database.lookup('j')

c = C(10, database=my_database)
```

We should avoid marking `InitVar` as typing-only, since it _is_ required
by the dataclass at runtime.

Note that by default, we _already_ don't flag this, since the
`@dataclass` member is needed at runtime too -- so it's only a problem
with `strict` mode.

Closes #9666.
@jonyscathe
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Thanks for the quick fix!
It is annoying that there are a handful of special cases like this in Python where the typing is actually used at runtime.

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Avoid marking InitVar as a typing-only annotation astral-sh/ruff
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@charliermarsh @jonyscathe