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attrs plugin should support attrs.evolve #14525

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ikonst opened this issue Jan 25, 2023 · 6 comments · Fixed by #14526
Closed

attrs plugin should support attrs.evolve #14525

ikonst opened this issue Jan 25, 2023 · 6 comments · Fixed by #14526
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feature topic-attrs

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@ikonst
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ikonst commented Jan 25, 2023 •
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Feature

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

Pitch

We should validate attr names and types match.
@ikonst ikonst added the feature label Jan 25, 2023
@ikonst ikonst mentioned this issue Jan 26, 2023
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@tmke8
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tmke8 commented Jan 27, 2023 •
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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
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ikonst commented Jan 27, 2023

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

@tmke8
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tmke8 commented Jan 27, 2023

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
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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
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ikonst commented Jan 27, 2023

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
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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.

@OlegAlexander OlegAlexander mentioned this issue Feb 26, 2023
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JelleZijlstra pushed a commit that referenced this issue Mar 6, 2023
@ikonst
Add signature for attr.evolve (#14526)
bbc9cce 
Validate `attr.evolve` calls to specify correct arguments and types.

The implementation makes it so that at every point where `attr.evolve`
is called, the signature is modified to expect the attrs class'
initializer's arguments (but so that they're all kw-only and optional).

Notes:
- Added `class dict: pass` to some fixtures files since our attrs type
stubs now have **kwargs and that triggers a `builtin.dict` lookup in
dozens of attrs tests.
- Looking up the type of the 1st argument with
`ctx.api.expr_checker.accept(inst_arg)` which is a hack since it's not
part of the plugin API. This is a compromise for due to #10216.

Fixes #14525.
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Add signature for attr.evolve ikonst/mypy
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@ikonst @tmke8 @AlexWaygood