Uncurry is picky about its erasure decision (when it shouldn't)

[scabug]

Following up on #6443 and #9442, is seems the uncurry erasure is quite picky:

$ cat test2.scala 
trait Ctx {
  trait Tree
}
trait Lst[+A] {
  def zip[A1 >: A, B](that: Lst[B]): Nothing
}
object Test {
  def foo1(c: Ctx)(l: Lst[c.Tree]) = l zip l
  def foo2[T](c: Ctx)(l: Lst[c.Tree])(t: T) = l zip l
}

$ scalac test2.scala -Xprint:uncurry
[[syntax trees at end of                   uncurry]] // test2.scala
package <empty> {
  abstract trait Ctx extends Object {
    def /*Ctx*/$init$(): Unit = {
      ()
    };
    abstract trait Tree extends Object
  };
  abstract trait Lst[+A] extends Object {
    def zip[A1 >: A, B](that: Lst[B]): Nothing
  };
  object Test extends Object {
    def <init>(): Test.type = {
      Test.super.<init>();
      ()
    };
    def foo1(c: Ctx, l: Lst[Ctx#Tree]): Nothing = {
      <synthetic> val l$1: Lst[c.Tree] = l.asInstanceOf[Lst[c.Tree]]();
      l$1.zip[c.Tree, c.Tree](l$1)
    };
    def foo2[T](c: Ctx, l: Lst[c.Tree], t: T): Nothing = l.zip[c.Tree, c.Tree](l)
  }
}

So, depending on whether you have a type parameter, it decides to erase or not:

    def foo1(c: Ctx, l: Lst[Ctx#Tree]): Nothing = {
      <synthetic> val l$1: Lst[c.Tree] = l.asInstanceOf[Lst[c.Tree]]();
      l$1.zip[c.Tree, c.Tree](l$1)
    };
    def foo2[T](c: Ctx, l: Lst[c.Tree], t: T): Nothing = l.zip[c.Tree, c.Tree](l)

I think the problem lies in the isDependentMethodType method in class Type, but I may be wrong:

$ scala
Welcome to Scala 2.11.8-20150821-135328-f8a6d21a49 (Java HotSpot(TM) 64-Bit Server VM, Java 1.7.0_80).
Type in expressions for evaluation. Or try :help.

scala> trait Ctx {
     |   trait Tree
     | }
defined trait Ctx

scala> trait Lst[+A] {
     |   def zip[A1 >: A, B](that: Lst[B]): Nothing
     | }
defined trait Lst

scala> object Test {
     |   def foo1(c: Ctx)(l: Lst[c.Tree]) = l zip l
     |   def foo2[T](c: Ctx)(l: Lst[c.Tree])(t: T) = l zip l
     | }
defined object Test

scala> import scala.reflect.runtime.universe._
import scala.reflect.runtime.universe._

scala> typeTag[Test.type].tpe.member(TermName("foo1")).info.asInstanceOf[scala.reflect.internal.Types#Type].isDependentMethodType
res0: Boolean = true

scala> typeTag[Test.type].tpe.member(TermName("foo2")).info.asInstanceOf[scala.reflect.internal.Types#Type].isDependentMethodType
res1: Boolean = false

[scabug]

Imported From: https://issues.scala-lang.org/browse/SI-9443?orig=1
Reporter: @VladUreche
Affected Versions: 2.10.5, 2.11.7, 2.12.0-M2
See #6443, #9442