Support PEP 681 (dataclass_transform)

[NeilGirdhar]

PEP 681 introduces a new decorator function in the typing module named dataclass_transform. This was added to Python 3.11.

See #5383 for a related issue that this would solve. See #12840 for MyPy's Python 3.11 issues.

[NeilGirdhar]

It would be really nice to support frozen_default, which is not part of the PEP, but was added to CPython (python/cpython#99957) and typing_extensions (python/typing_extensions#101).

[tmke8]

Python 3.11 (to be released in one year)

Hm? Python 3.11 has already been released.

[NeilGirdhar]

@thomkeh Thanks for catching my mistake, edited 😄

[hauntsaninja]

Just to keep this issue up to date:

mypy 1.0 shipped with extremely rudimentary support for dataclass_transform decorator with no parameters passed. mypy master has increasingly better support for PEP 681.

[NeilGirdhar]

@wesleywright Looks like this complete on master? If so, I'll close this issue. Please feel free to tick this off the Python 3.11 issue.

[wesleywright]

@NeilGirdhar Yes, as far as I'm aware we're feature complete on master now.

[tmke8]

Does the implementation support taking into account overloads to determine whether a field will be present in the __init__? The master version in mypy play doesn't seem to support it: https://mypy-play.net/?mypy=master&python=3.11&gist=eec5f42639277ba0988d496cee03d3d4

The example is from this section of the PEP: https://peps.python.org/pep-0681/#field-specifier-parameters