Fix needsProtectedAccessor check

A protected accessor is not needed if the current class self-type is a
subtype of the accessed symbol, but the logic to check this was broken
before this commit and looked at the host class self-type instead.

Author: smarter

compiler/src/dotty/tools/dotc/transform/SuperAccessors.scala

@@ -300,9 +300,8 @@ class SuperAccessors(thisTransformer: DenotTransformer) {
     private def needsProtectedAccessor(sym: Symbol, pos: Position)(implicit ctx: Context): Boolean = {
       val clazz = currentClass
       val host = hostForAccessorOf(sym, clazz)
-      val selfType = host.classInfo.selfType
       def accessibleThroughSubclassing =
-        validCurrentClass && (selfType <:< sym.owner.typeRef) && !clazz.is(Trait)
+        validCurrentClass && (clazz.classInfo.selfType <:< sym.owner.typeRef) && !clazz.is(Trait)
 
       val isCandidate = (
            sym.is(Protected)
@@ -312,9 +311,11 @@ class SuperAccessors(thisTransformer: DenotTransformer) {
         && (sym.enclosingPackageClass != currentClass.enclosingPackageClass)
         && (sym.enclosingPackageClass == sym.accessBoundary(sym.enclosingPackageClass))
       )
-      def isSelfType = !(host.typeRef <:< selfType) && {
-        if (selfType.typeSymbol.is(JavaDefined))
-          ctx.restrictionError(s"cannot accesses protected $sym from within $clazz with self type $selfType", pos)
+      val hostSelfType = host.classInfo.selfType
+      def isSelfType = !(host.typeRef <:< hostSelfType) && {
+        if (hostSelfType.typeSymbol.is(JavaDefined))
+          ctx.restrictionError(
+            s"cannot accesses protected $sym from within $clazz with host self type $hostSelfType", pos)
         true
       }
       def isJavaProtected = host.is(Trait) && sym.is(JavaDefined) && {