Implicit derivation failing when using cached implicits + orphan derivation at the same time

[alexarchambault]

See the last two commits here: https://github.com/alexarchambault/argonaut-shapeless/commits/test/orphans and here: https://github.com/alexarchambault/scalacheck-shapeless/commits/test/orphans.

Cached implicits were enabled. The first of the two commits enables orphan derivation by default, which breaks implicit derivation. The last of the two commits disables cached implicits, which makes things work again.

I'm afraid I can't derive a minimalist example right now... The code bases of argonaut-shapeless and scalacheck-shapeless aren't that large though.

[milessabin]

It'd be really helpful if you could find some time to post a minimization. I'll punt this until the next release for now.

[alexarchambault]

I finally set up a minimal example here: https://github.com/alexarchambault/shapeless-cached-implicits-vs-orphan-derivation

It seems that implicit derivation through the fails with orphan derivers. (And cachedImplicit is using the internally.)

But it doesn't seem to happen all the time, and I wasn't able to reproduce it with more minimal type classes. That's why the example uses argonaut.

[milessabin]

Thanks for that ...

[milessabin]

This doesn't solve the problem for the in general, but it does solve the problem for cachedImplicit by replacing the with implicitly in its expansion.