Modified return type inference not to allow T* ...

Modified return type inference not to allow T* to leak from varargs
methods. Since I don't know what is supposed to be done about eta
expansion of these methods, I left the behavior as it was (except the
return type) and a boolean val in Types to change it.

  def id[T](xs: T*) = xs
  etaExpandKeepsStar = true   // (id[Int] _) is Int* => Seq[Int]
  etaExpandKeepsStar = false  // (id[Int] _) is Seq[Int] => Seq[Int]

References #4176, leaving open pending resolution of eta expansion.
Review by odersky.

1 files changed, 21 insertions, 0 deletions

diff --git a/src/compiler/scala/reflect/internal/Types.scala b/src/compiler/scala/reflect/internal/Types.scala
index 75243c6e1c..840d66c558 100644
--- a/src/compiler/scala/reflect/internal/Types.scala
+++ b/src/compiler/scala/reflect/internal/Types.scala
@@ -2995,6 +2995,27 @@ A type's typeSymbol should never be inspected directly.
     }
   }
 
+  // Set to true for A* => Seq[A]
+  //   (And it will only rewrite A* in method result types.)
+  //   This is the pre-existing behavior.
+  // Or false for Seq[A] => Seq[A]
+  //   (It will rewrite A* everywhere but method parameters.)
+  //   This is the specified behavior.
+  private final val etaExpandKeepsStar = true
+
+  object dropRepeatedParamType extends TypeMap {
+    def apply(tp: Type): Type = tp match {
+      case MethodType(params, restpe) =>
+        MethodType(params, apply(restpe))
+      case PolyType(tparams, restpe) =>
+        PolyType(tparams, apply(restpe))
+      case TypeRef(_, RepeatedParamClass, arg :: Nil) =>
+        seqType(arg)
+      case _ =>
+        if (etaExpandKeepsStar) tp else mapOver(tp)
+    }
+  }
+
 // Hash consing --------------------------------------------------------------
 
   private val initialUniquesCapacity = 4096