Implement PEP 681 (@dataclass_transform)

[JelleZijlstra]

The SC has given the green light to implement PEP 681 in Python 3.11: https://mail.python.org/archives/list/typing-sig@python.org/thread/JWMSWJ6JZJNNG3JKPBYDMQUUHZFD2FZL/

I'll send a PR shortly to add the runtime implementation. As with PEP 655, I'll hold off on documentation to make sure we get the runtime code in before the feature freeze in a few weeks.

cc @debonte @erictraut

[bluetech]

Is there an intention to apply @dataclass_transform to dataclasses.dataclass itself?

[JelleZijlstra]

Is there an intention to apply @dataclass_transform to dataclasses.dataclass itself?

I haven't considered it. For performance reasons dataclasses.py avoids importing typing, which presents a problem for doing it at runtime. We could apply the decorator in typeshed, probably based on feedback from type checker authors.

[bluetech]

If it is decided to apply it in typeshed, the effect of the decorator (the __dataclass_transform__ attribute) can be added manually to dataclass, perhaps with some test to ensure consistency.

[erictraut]

I don't see any benefit to using @dataclass_transform with dataclass.dataclass. All existing type checkers already know about dataclass.