Case where -Ypartial-unification fails #10310
Description
Simplified/standalone version of the first failure case I'm hitting from tierney. testSuccess compiles (by passing explicit type parameters), testFail does not (even with -Ypartial-unification) whereas I would (maybe) expect it to?
object Demo {
trait Free1[F[_], A]
trait Free2[F[_], A]
trait Cp[F[_], G[_], A]
class Fix[W[_[_[_], _], _[_], _], F[_], A]()
type Unfixed[S[_[_], _], F[_], A] =
Cp[F, Free1[Free2[S[F, ?], ?], ?], A]
trait Command[A]
def unify[F[_], A](value: F[A]): Unit = {}
def testSuccess(v: Free2[Fix[Unfixed, Command, ?], String]) =
unify[Free2[Fix[Unfixed, Command, ?], ?], String](v)
def testFail(v: Free2[Fix[Unfixed, Command, ?], String]) =
unify(v)
}