attrs plugin should support attrs.evolve

[ikonst]

Feature

In the attrs plugin, we should add special treatment for attrs.evolve.

Pitch

We should validate attr names and types match.

[tmke8]

Similar treatment for dataclasses.replace would also be nice. (There was previously PR #14263 but that one only checked that the first argument to replace is a dataclass – which can also be done by just modifying the type stubs.)

[ikonst]

By modifying the type annotations? I don't think dataclasses have any common base, do they? Or maybe through a protocol?

[tmke8]

By modifying the type annotations? I don't think dataclasses have any common base, do they? Or maybe through a protocol?

Yes, @AlexWaygood suggested doing it with a protocol: python/typeshed#9362

[AlexWaygood]

By modifying the type annotations? I don't think dataclasses have any common base, do they? Or maybe through a protocol?

Yes, @AlexWaygood suggested doing it with a protocol: python/typeshed#9362

Applying the same technique to attrs would be difficult unless all type checkers could be counted on to synthesise __attrs_attrs__ attributes for attrs classes in the same way that they can be counted on to synthesise __dataclass_fields__ attributes for classes decorated with @dataclass. Mypy has a custom plugin for attrs, meaning it can be counted on to synthesise this attribute. On the other hand, pyright has (reasonably) resisted adding any special-casing for any third-party libraries.

[ikonst]

If attrs ships its own type annotations, then they could decide that e.g. you could only used them with mypy and a certain plugin being installed, but I agree we cannot make this decision for typeshed's annotations.

And for this case, the plugin can easily make this check, and I would have to in #14526 anyway.

[AlexWaygood]

To be clear, attrs does ship its own type annotations, and typeshed does not have stubs for attrs. If somebody did want to try a solution for attrs along the lines of my dataclasses PR to typeshed, they'd have to implement it in the annotations shipped by attrs, not in typeshed.