Apply changes of code review

Author: b-studios

compiler/src/dotty/tools/dotc/typer/RefChecks.scala

@@ -786,32 +786,29 @@ object RefChecks {
       //
       // In particular, it checks that there are no two base classes with
       // different type instantiations.
-      //
-      // ported from Scala 2:
-      //   https://github.com/scala/scala/blob/9bb659e62a9239c01aec14c171f8598bb1a576fe/src/compiler/scala/tools/nsc/typechecker/RefChecks.scala#L834-L883
       def validateBaseTypes(): Unit = {
         val tpe = clazz.thisType // in Scala 2 this was clazz.tpe
         val seenParents = mutable.HashSet[Type]()
         val baseClasses: List[ClassSymbol] = clazz.info.baseClasses
 
         // tracks types that we have seen for a particular base class in baseClasses
-        val seenTypes = mutable.Map.empty[Symbol, List[Type]]
+        val seenTypes = MutableSymbolMap[List[Type]](baseClasses.size)
 
         // validate all base types of a class in reverse linear order.
         def register(tp: Type): Unit = {
-          val baseClass = tp.typeSymbol
+          val baseClass = tp.classSymbol
           if (baseClasses contains baseClass) {
             val alreadySeen = seenTypes.getOrElse(baseClass, Nil)
-            if (alreadySeen.forall { tp1 => !(tp1 <:< tp) })
-              seenTypes.update(baseClass, tp :: alreadySeen.filter { tp1 => !(tp <:< tp1) })
+            if (alreadySeen.forall(tp1 => !(tp1 <:< tp)))
+              seenTypes.update(baseClass, tp :: alreadySeen.filter(tp1 => !(tp <:< tp1)))
           }
           val remaining = tp.parents filterNot seenParents
           seenParents ++= remaining
           remaining foreach register
         }
         register(tpe)
 
-        seenTypes.foreach {
+        seenTypes.iterator.foreach {
           case (cls, Nil) =>
             assert(false) // this case should not be reachable
           case (cls, _ :: Nil) =>