attrs plugin does not support generic type

Bug Report

The mypy attrs plugin has custom support for attrs.evolve, which has different code branches for regular and generic types (starting here).

It admits attrs.has as a type guard for attrs.evolve if the original type is Any, but not if it's a generic type parameter T with no type bound.

To Reproduce

On python 3.12 (so lacking copy.replace):

def replace[T](value: T, **kwargs: Any) -> T:
    if attrs.has(type(value)):
        return attrs.evolve(value, **kwargs)
    else:
        raise NotImplementedError(f"replace is not implemented for {type(value)}")

Mypy reports, error: Argument 1 to "evolve" has a variable type "T" not bound to an attrs class [misc]

(In the actual code I'd do something else in other branches; this is intended as a replacement for copy.replace on python < 3.13, supporting different types besides attrs classes.)

Using the attr.AttrInstance protocol also doesn't work, which means I can't define my own type guard wrapping attrs.has. This code results in the same mypy error:

def replace[T: attrs.AttrsInstance](value: T, **kwargs: Any) -> T:
    return attrs.evolve(value, **kwargs)

However, this code works (and is a viable workaround):

def replace[T](value: T, **kwargs: Any) -> T:
    val2: Any = value
    if attrs.has(type(val2)):
        return attrs.evolve(val2, **kwargs)
    else:
        raise NotImplementedError(f"replace is not implemented for {type(value)}")

Expected Behavior

Mypy should honor attrs.has as a type guard for attrs.evolve, whether the original type is generic or any other kind.

• Mypy version used: 1.15.0
• Python version used: 3.12.10

mypy/plugins/attrs.py の 914 行目付近にある attrs.evolve の処理から始め、提供されている Python 3.12 のジェネリック例を mypy 1.15.0 に対して実行して診断を確認します。attrs.has が Any と未束縛の型パラメーターでそれぞれどのように認識されるかを追跡し、ジェネリック例が変数型エラーなしで受け入れられ、期待される戻り値の型が維持されることを確認して完了とします。