SI-9442 Fix the uncurry-erasure types

Using the "uncurry-erased" type (the one after the uncurry phase) can
lead to incorrect tree transformations. For example, compiling:
```
  def foo(c: Ctx)(l: c.Tree): Unit = {
    val l2: c.Tree = l
  }
```
Results in the following AST:
```
  def foo(c: Ctx, l: Ctx#Tree): Unit = {
    val l$1: Ctx#Tree = l.asInstanceOf[Ctx#Tree]
    val l2: c.Tree = l$1 // no, not really, it's not.
  }
```
Of course, this is incorrect, since `l$1` has type `Ctx#Tree`, which is
not a subtype of `c.Tree`.

So what we need to do is to use the pre-uncurry type when creating
`l$1`, which is `c.Tree` and is correct. Now, there are two
additional problems:

1. when varargs and byname params are involved, the uncurry
   transformation desugares these special cases to actual
   typerefs, eg:
   ```
          T*  ~> Seq[T] (Scala-defined varargs)
          T*  ~> Array[T] (Java-defined varargs)
          =>T ~> Function0[T] (by name params)
   ```
   we use the DesugaredParameterType object (defined in
   scala.reflect.internal.transform.UnCurry) to redo this desugaring
   manually here
2. the type needs to be normalized, since `gen.mkCast` checks this
   (no HK here, just aliases have to be expanded before handing the
   type to `gen.mkAttributedCast`, which calls `gen.mkCast`)

1 files changed, 1 insertions, 1 deletions

diff --git a/src/reflect/scala/reflect/runtime/JavaUniverseForce.scala b/src/reflect/scala/reflect/runtime/JavaUniverseForce.scala
index ea213cadd9..5477bdd6d4 100644
--- a/src/reflect/scala/reflect/runtime/JavaUniverseForce.scala
+++ b/src/reflect/scala/reflect/runtime/JavaUniverseForce.scala
@@ -444,7 +444,7 @@ trait JavaUniverseForce { self: runtime.JavaUniverse  =>
     definitions.ScalaValueClassesNoUnit
     definitions.ScalaValueClasses
 
-
+    uncurry.DesugaredParameterType
     erasure.GenericArray
     erasure.scalaErasure
     erasure.specialScalaErasure