st.from_types with Union and Protocol weirdly requires int not to throw

[ClementWalter]

I've managed to extract this MWE from my buggy tests

from typing import ClassVar, Dict, ForwardRef, Protocol, Sequence, TypeAlias, Union

from hypothesis import given, settings
from hypothesis import strategies as st


class IsDataclass(Protocol):
    __dataclass_fields__: ClassVar[Dict]


Extended: TypeAlias = Union[Sequence["Extended"], int, bool, bytes, IsDataclass]

st.register_type_strategy(IsDataclass, st.just(b""))
st.register_type_strategy(
    ForwardRef("Extended"),
    st.recursive(st.one_of(st.integers(), st.booleans(), st.binary()), st.tuples),
)


@given(a=...)
@settings(max_examples=1000)
def test_extended(a: Extended):
    print(a)

Defining Extended without int, ie just like

Extended: TypeAlias = Union[Sequence["Extended"], bool, bytes, IsDataclass]

will crash with

E           TypeError: Instance and class checks can only be used with @runtime_checkable protocols

I'm using python3.10 and from my uv.lock I see

[[package]]
name = "hypothesis"
version = "6.112.1"
source = { registry = "https://pypi.org/simple" }
dependencies = [
    { name = "attrs" },
    { name = "exceptiongroup", marker = "python_full_version < '3.11'" },
    { name = "sortedcontainers" },
]

[Zac-HD]

Well, that's definitely not ideal - but I think the intended behavior is to throw even if int is included, because isinstance(x, IsDataclass) will raise TypeError: Instance and class checks can only be used with @runtime_checkable protocols without Hypothesis involved at all. (and st.from_type() has to be able to check isinstance()/issubclass() to work)

So our main project is to work out why adding int stops that error from appearing, and see if we can make it consistent 🙂