inference regression with aliased existential #6014
Description
This almost has to be a duplicate of something, but I can't find it and it's bad, so opening until I or someone finds the duplicate. This compiles with 2.9.2.
object Test {
case class CC[T](key: T)
type Alias[T] = Seq[CC[T]]
def f(xs: Seq[CC[_]]) = xs map { case CC(x) => CC(x) } // ok
def g(xs: Alias[_]) = xs map { case CC(x) => CC(x) } // fails
// ./a.scala:11: error: missing parameter type for expanded function
// The argument types of an anonymous function must be fully known. (SLS 8.5)
// Expected type was: ?
// def g(xs: Alias[_]) = xs map { case CC(x) => CC(x) } // fails
// ^
// one error found
}