Fix dealiasing of types which caused test failures in TypeMismatch errors

Author: ausmarton

compiler/src/dotty/tools/dotc/printing/PlainPrinter.scala

@@ -193,9 +193,9 @@ class PlainPrinter(_ctx: Context) extends Printer {
         "<overloaded " ~ toTextRef(tp) ~ ">"
       case tp: TypeRef =>
         if (printWithoutPrefix.contains(tp.symbol))
-          selectionString(tp.dealias.typeSymbol.namedType)
+          selectionString(tp)
         else
-          toTextPrefixOf(tp) ~ selectionString(tp.dealias.typeSymbol.namedType)
+          toTextPrefixOf(tp) ~ selectionString(tp)
       case tp: TermParamRef =>
         ParamRefNameString(tp) ~ lambdaHash(tp.binder) ~ ".type"
       case tp: TypeParamRef =>

compiler/src/dotty/tools/dotc/reporting/Message.scala

@@ -88,7 +88,7 @@ object Message:
       def followAlias(e1: Recorded): Recorded = e1 match {
         case e1: Symbol if e1.isAliasType =>
           val underlying = e1.typeRef.underlyingClassRef(refinementOK = false).typeSymbol
-          if (underlying.name == e1.name) underlying else e1
+          if (underlying.name == e1.name) underlying else e1.namedType.dealias.typeSymbol
         case _ => e1
       }
       val key = SeenKey(str, isType)