Cogen[TestsDefinitions.T1.Tree] crashes about scalacheck-shapeless HOT 5 CLOSED

I forgot auto closing doesn't work from comments. This is fixed now.

from scalacheck-shapeless.

That's to be expected since MkHListCogen and MkCoproductCogen are Strict in the head. I don't know if this is intended, because sometimes special care is needed to deal with recursive types (e.g. Gen.lzy). But you can try to use Lazy and see what happens.

from scalacheck-shapeless.

Changing the head to Lazy makes the expression Cogen[T1.Tree] compile successfully, but I don't know if the generated value is correct. Would be great if someone who is familiar with the internals could take a look.

from scalacheck-shapeless.

Actually the generic Repr implicits are already wrapped in Lazy here. So support for recursive types is intended. I think the issue is that calling contramap in the implementation forces evaluation too early. Replacing it with this seems to work:

instance(Cogen { (seed: Seed, p: P) =>
  cogen.value.cogen.perturb(seed, gen.to(p))
})

Note how cogen.value.cogen is not forced until the perturb function is actually called. Would you like to make a PR with this fix and the added test with T1.Tree?

from scalacheck-shapeless.

Should be fixed in master, yep. I'll do a release once #73 and #74 are settled.

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