I'm pretty sure I'm hitting a limitation here, but I guess it's worth a shot just asking I've got a rule that returns an instance of a subclass of a custom object (call it

Letter

) If I've got, say

A

and

B

, it seems to be impossible to create a rule, because it doesn't accept

TypeVar

return type The only "workaround" I found is to create a custom dataclass with a single property

letter

and then have that as the return value, but that's cumbersome because every time I use it I have to go

letter.letter.<my_attr>

Is there a better way?

You are likely hitting the limitation that the engine only looks at the exact type of the return type in assembling the rule graph. That is, the engine is type invariant.

I see

Not sure we want to advertise this, but there is a (undocumented) power-feature that may fit, depending on your situation.. https://github.com/pantsbuild/pants/pull/16929

Oh, wow... Looks quite funky.. But I'll take a look anyway Thanks

yea, guess it became more of a curiosity 😅