Support PEP 695 syntax for class definitions

[JelleZijlstra]

PEP 695, which is implemented in the upcoming Python 3.12, adds a new syntax for defining generic classes:

class Sequence[T]:
     def __getitem__(self, idx: int) -> T: ...

I would like to document generic classes with e.g. .. class:: Sequence[T], but that doesn't render correctly (the class introduction doesn't appear):

Presumably the parser for the class directive needs to be taught to recognize this syntax. (Cross-ref: python/cpython#104642 (comment).)

[picnixz]

The issue lies in

sphinx/sphinx/domains/python.py

Lines 42 to 49 in d3c91f9

	# REs for Python signatures
	py_sig_re = re.compile(
	r'''^ ([\w.]*\.)? # class name(s)
	(\w+) \s* # thing name
	(?: \(\s*(.*)\s*\) # optional: arguments
	(?:\s* -> \s* (.*))? # return annotation
	)? $ # and nothing more
	''', re.VERBOSE)

We need a better regular expression for matching this new signature. If anyone knows some magical regex for that (otherwise I'll think of it this w-e).

[Gobot1234]

Just adding a smidge to this it'd also be nice for it to work for functions as well doesn't matter I've seen the PR now