Generate Python typing compatible text signatures (and stubs)

My .pyx file uses a PEP-484 style type signature:

#cython: embedsignature=True
def f(path: str, a: int = 0, b: bool = True) -> typing.List[str]:
    return []

Cython 0.29.13 turns this into the docstring: f(unicode path: str, a: int = 0, bool b: bool = True) -> typing.List[str] (see also #1370 for “unicode”)

When using mypy-stubgen, that docstring turns into: def f(unicodepath: str, a: int = ..., boolb: bool = ...) -> typing.List[str]: ...

Which causes mypy false positives for Python code calling f with a named argument for b.

I think embedsignature should not output Cython-specific syntax, as that breaks tooling consuming these docstrings. Ideally it’d also convert Cython signatures into the corresponding Python signatures; but it would be good enough for me if it just left PEP484 signatures as-is.

[scoder]

If generating .pyi stubs is not too complex, Cython could do it automatically, yes, similar to how it now generates the embedded signatures in AutoDocTransform. PR welcome.

I also agree that generating ‘normal’ Py3 annotations would be nicer than generating Cython syntax. PR welcome for that, too.

[cmpute]

Looking forward to this functionality! I usually write all documentation in .pyx files, so it could be very nice to have automatic .pyi generation!