Feature Request: make builds() understand __wrapped__ functions

[pschanely]

Per the docs, the hypothesis builds function uses python's getfullargspec to determine parameters. Sadly, this means that some traditional ways of wrapping functions will hide the real parameters.

An example:

from hypothesis import given, infer
from functools import wraps

def logged(f):
    @wraps(f)
    def wrapper(*a, **kw):
        print('I was called')
        return f(*a, **kw)
    return wrapper

class Foo:
    @logged
    def __init__(self, i: int):
	    pass

@given(foo = infer)
def test_foo_test(foo: Foo):
    assert True

test_foo_test()

This yields the follow error:

TypeError: __init__() missing 1 required positional argument: 'i'

I suspect that using inspect's signature function would help here, but that might be a pretty invasive change?

[Zac-HD]

IMO this is clearly justified; cases where signature's default follow_wrapped=True is counterproductive do exist but are very rare.

#2218 even has "consider replacing uses of inspect.getfullargspec with inspect.signature" as one of the remaining checklist items - and while I didn't get around to that as part of our more general dropping-python-2 code modernisation, it shouldn't be that big a deal to do so now.

[Zac-HD]

Aaaaand, it breaks a lot of subtle things: master...Zac-HD:signature-upgrade

There might be something small and crucial that I missed, but 🤷‍♂️ I'm leaving it for now.