hey folks, I'm working on helpers to generate the lockfile rules. For testing, I'd like to set a query rule for the lockfile sentinel (eg

Flake8LockfileSentinel

). Problem is, that class now exists only at runtime. Is there a simple way to go from the tool (

class Flake8(PythonToolBase):

) to whatever the concrete class of the UnionRule is ( whatever was used as the 2nd argument in`UnionRule(GenerateToolLockfileSentinel, Flake8LockfileSentinel)`) ? I could fish it out of the generated rules, but that doesn't seem like something Pants wants anyone to do.

I guess this information exists in the

UnionMembership

? so perhaps something like:

@rule
async def get_concrete_class(union_membership: UnionMembership) -> x:
  for member_cls in union_membership.get(GenerateToolLockfileSentinel):
    if is_what_i_want(member_cls):
      ...

would need some common base class or other to identify the concrete class with among all the registered sentinel classes I guess..

Yeah, I think that would work. In small tests there's probably only one class in the union membership, and I think there might be a options_scope parameter for that sort of unionmembership

do you have a link to the code for this? I guess you want to make the dynamic class memoized per class instance, then you can pull the exact same class for your test that is going to be registered in the union rule. c.f. https://github.com/pantsbuild/pants/blob/eee5863b85a995c25d210ecee57b93d2dfaedbc3/src/python/pants/engine/target.py#L479-L481

I'll look into that, thanks. Here's the method I have currently link, and here's how I use it link

and where is the lockfile sentinel generated?

Invocation of generation here, definition of generation resolves to here

Ah.. right. Buried deep 😛 Fishing the class out from the union rule in the rules graph seems fine to me for testing purposes..