Add support for attribute docstrings

[tibdex]

The goal of this issue is to get Ruff to lint and format attribute docstrings as already done for class/method/function docstrings.

PEP 224 is about attribute docstrings. It was rejected but its proposed syntax (where a triple quote string can be placed under a class attribute to document it) has become a de facto standard:

• Pyright/Pylance/VS Code supports it (added in https://github.com/microsoft/pyright/issues/2106 and https://github.com/microsoft/pyright/commit/ea60aafef03d10a7f28c543b10941fcc4cd08a09).
• Sphinx supports it with the :autoattribute: directive.

For example, with this code:

from dataclasses import dataclass

@dataclass
class Demo:
    """Demo."""

    value: int
    """The value."""

Sphinx outputs the expected HTML:

and shpinx.ext.doctest would even detect interactive Python sessions in value's docstring and check them.

VS Code also shows the attribute docstring on hover:

On the other hand, with this code trying to document the attribute in a Google style docstring:

from dataclasses import dataclass

@dataclass
class Demo:
    """Demo.

    Attributes:
        value: The value.
    """

    value: int

Sphinx, even with sphinx.ext.napoleon correctly configured, duplicates the attribute:

and VS Code does not show the docstring on hover:

Would you consider detecting this syntax as attribute docstrings and handling them like the other docstrings (e.g. formatting code examples in them)?

[!NOTE] PEP 727 is a draft suggesting to document attributes like this:

from typing import Annotated, Doc

class Demo:
    value: Annotated[int, Doc("The value.")]

typing-extensions already provides it but Sphinx and VS Code do not support it.

[charliermarsh]

I'm generally supportive of this.

[dhruvmanila]

Ruff can now detect this via https://github.com/astral-sh/ruff/pull/11315 although it's currently not being used anywhere (linter or formatter).