Conformance: align dataclass descriptor tests with runtime by ashishpatel26 · Pull Request #2299 · python/typing

Closes #2259.

dataclasses_descriptors.py keeps coverage for the non-data descriptor (Desc2, only __get__) used as a dataclass field, but aligns the expected behavior with runtime descriptor lookup:

• DC2.x / DC2.y class access is optional-error because those fields have no descriptor object in the class namespace.
• DC2.z class access is list[str], because class access invokes Desc2.__get__(None, owner).
• dc2.x / dc2.y / dc2.z are the stored Desc2[...] objects, because non-data descriptors are shadowed by the instance __dict__ after dataclass __init__ assigns the fields.

The result TOMLs and summary HTML have been regenerated. With the runtime-correct asserts, all six checkers are scored Partial for dataclasses_descriptors.

What - in your opinion - would be the proper solution for these cases? I generally want to avoid removing tests and rather expand the docs or correct the tests. There are a lot of cases where the spec is lacking and I want to avoid removing them all.

In my opinion it is very valuable to standardize descriptors on Dataclasses. I'm not particularly invested in how they are standardized, but I would like to have that to be one specific way.

As I wrote in the issue, pyrefly's behavior seemed the most correct to me. I'm not sure this behavior needs to be specified in the typing spec in much detail since what I view as the correct behavior primarily reflects the runtime.

pyrefly's behavior seemed the most correct to me. I'm not sure this behavior needs to be specified in the typing spec in much detail since what I view as the correct behavior primarily reflects the runtime.

I agree that this does not necessarily need to be specified. However I would still prefer to make the pyrefly behavior part of the tests than to drop the test.

Thanks both. I reworked this to keep the non-data descriptor coverage rather than deleting it, and aligned the DC2 case with runtime descriptor lookup:

• DC2.x / DC2.y class access remains optional-error because those fields have no class attribute at runtime.
• DC2.z class access is asserted as list[str], since class access invokes Desc2.__get__(None, owner).
• dc2.x / dc2.y / dc2.z are asserted as the stored Desc2[...] objects, because a non-data descriptor is shadowed by the instance __dict__ after dataclass __init__ assigns the fields.

I regenerated the result files and summary HTML for this test. With the runtime-correct asserts, all six checker result TOMLs are now scored Partial for dataclasses_descriptors.