from_type on typing.Protocol without methods

[Rik-de-Kort]

I'm expecting a protocol without any methods to be able to passed in to from_type, but that doesn't work.
Additionally, a bare class with only class variables can also not be passed to from_type, but a dataclass can.

import typing

from hypothesis import given, strategies as st

@typing.runtime_checkable
class NoMethods(typing.Protocol):
    x: float

@given(st.from_type(NoMethods)
def test_can_handle_methodless_protocols(data):
    assert data.x is not None

Fails with message:
FAILED test.py::test_can_handle_methodless_protocols - TypeError: Protocols with non-method members don't support issubclass()

The bare class example:

from hypothesis import given, strategies as st

class NoMethods:
    x: float

@given(st.from_type(NoMethods))
def test_can_handle_methodless_protocols(no_methods):
    assert no_methods.x is not None

Fails with message:
FAILED test.py::test_can_handle_methodless_protocols - AttributeError: 'NoMethods' object has no attribute 'x'

The dataclass example:

from dataclasses import dataclass

from hypothesis import given, strategies as st

@dataclass
class NoMethods:
    x: float

@given(st.from_type(NoMethods))
def test_can_handle_methodless_protocols(no_methods):
    assert no_methods.x is not None

does pass. I would expect all of them to

On the other hand, a protocol is a non-runtime thing, so maybe there should be a separate strategy from_protocol?

[Zac-HD]

• Your NoMethods protocol is not actually runtime-checkable (because it has non-method attributes), so Hypothesis can't handle this at runtime. Unfortunate, but nothing we can do there.
• from_type() successfully generates instances of the bare class - the fact that this doesn't actually ensure that the x attribute exists is not Hypothesis' problem.
• @dataclass generates an __init__() method which takes a float x and assigns it to an attribute, so this works.

An internal _from_protocol() strategy to use for non-runtime-checkable protocols would be technically feasible, but providing objects with no useful behavior which technically satisfy the protocol just doesn't seem very useful to me.