Fixing hashing for RefinedThis types.

... to bring it in sync with equals.

Author: odersky

src/dotty/tools/dotc/core/Hashable.scala

@@ -33,7 +33,7 @@ trait Hashable {
   private def finishHash(hashCode: Int, arity: Int): Int =
     avoidNotCached(hashing.finalizeHash(hashCode, arity))
 
-  protected final def identityHash = avoidNotCached(System.identityHashCode(this))
+  final def identityHash = avoidNotCached(System.identityHashCode(this))
 
   private def finishHash(seed: Int, arity: Int, tp: Type): Int = {
     val elemHash = tp.hash

src/dotty/tools/dotc/core/Types.scala

@@ -1757,7 +1757,7 @@ object Types {
       }
   }
 
-  // ----- Bound types: MethodParam, PolyParam, RefiendThis --------------------------
+  // ----- Bound types: MethodParam, PolyParam, RefinedThis --------------------------
 
   abstract class BoundType extends CachedProxyType with ValueType {
     type BT <: BindingType
@@ -1821,7 +1821,7 @@ object Types {
 
     // need to customize hashCode and equals to prevent infinite recursion for
     // refinements that refer to the refinement type via this
-    override def computeHash = identityHash
+    override def computeHash = addDelta(binder.identityHash, 41)
     override def equals(that: Any) = that match {
       case that: RefinedThis => this.binder eq that.binder
       case _ => false