`match_args`, `slots` and possibly `kw_only` missing from `__dataclass_params__`

[da-woods]

Bug report

Dataclasses have an undocumented __dataclass_params__ class-attribute which appears to document the flags sent to the dataclass decorator:

cpython/Lib/dataclasses.py

Lines 903 to 904 in 6ec57e7

	setattr(cls, _PARAMS, _DataclassParams(init, repr, eq, order,
	unsafe_hash, frozen))

A few new flags have been added since the initial implementation of dataclasses. These don't seem to have been added to the __dataclass_params__ field. In the case of kw_only I think that makes sense - it's effectively controlled at a per-field level and the parameter to the dataclass decorator is just a convenience. However, the others seem like a genuine omission.

Your environment

I've just looked at the code for the current main branch.

[ericvsmith]

Thanks, @sobolevn !