Avoid setter in Name

and fix a bug in TreeUnpickler

Author: odersky

compiler/src/dotty/tools/dotc/core/Names.scala

@@ -346,7 +346,7 @@ object Names {
     def isSimple = false
     def asSimpleName = throw new UnsupportedOperationException(s"$debugString is not a simple name")
 
-    private var simpleName: SimpleTermName = null
+    private[this] var simpleName: SimpleTermName = null
     def toSimpleName = {
       if (simpleName == null) simpleName = termName(toString)
       simpleName

compiler/src/dotty/tools/dotc/core/tasty/TreeUnpickler.scala

@@ -416,8 +416,8 @@ class TreeUnpickler(reader: TastyReader, nameAtRef: NameRef => TermName, posUnpi
       val tag = readByte()
       val end = readEnd()
       var name: Name = readName()
-      val mname = name.mangled
       if (tag == TYPEDEF || tag == TYPEPARAM) name = name.toTypeName
+      val mname = name.mangled
       skipParams()
       val ttag = nextUnsharedTag
       val isAbsType = isAbstractType(ttag)