Attrs typing inference does not work with types from the typing module

[Meallia]

When trying to use builds or from_type strategies with an attrs class using generic classes from the typing module such as List[x], Union[x,y] or Dict[x,y] hypothesis fails.

Trying to create a strategy from this class:

@attr.s
class Inferrables(object):
    type_typing_list = attr.ib(type=typing.List[int])
    type_typing_dict = attr.ib(type=typing.Dict[str, int])
    type_typing_union = attr.ib(type=typing.Union[str, int])

@given(st.from_type(Inferrables))
def test_attrs_inference_from_type(c):
    pass

Would fail with

hypothesis.errors.ResolutionFailed: Cannot infer a strategy from the default, validator, type, or converter for attribute=Attribute(name='type_typing_union', default=NOTHING, validator=None, repr=True, cmp=True, hash=None, init=True, metadata=mappingproxy({}), type=typing.Union[str, int], converter=None, kw_only=False) of class=<class 'tests.cover.test_attrs_inference.Inferrables'>