Fix parent class for anonymous class

`Any` can be parent class of traits, in that case we should
choose `AnyRef`.

Author: liufengyun

compiler/src/dotty/tools/dotc/ast/tpd.scala

@@ -308,7 +308,10 @@ object tpd extends Trees.Instance[Type] with TypedTreeInfo {
   def AnonClass(parents: List[Type], fns: List[TermSymbol], methNames: List[TermName])(implicit ctx: Context): Block = {
     val owner = fns.head.owner
     val parents1 =
-      if (parents.head.classSymbol.is(Trait)) parents.head.parents.head :: parents
+      if (parents.head.classSymbol.is(Trait)) {
+        val head = parents.head.parents.head
+        if (head.isRef(defn.AnyClass)) defn.AnyRefType :: parents else head :: parents
+      }
       else parents
     val cls = ctx.newNormalizedClassSymbol(owner, tpnme.ANON_CLASS, Synthetic | Final, parents1,
         coord = fns.map(_.span).reduceLeft(_ union _))

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

@@ -515,7 +515,7 @@ class Typer extends Namer
       case templ: untpd.Template =>
         import untpd._
         var templ1 = templ
-        def isEligible(tp: Type) = tp.exists && !tp.typeSymbol.is(Final) && tp.classSymbol != defn.AnyClass
+        def isEligible(tp: Type) = tp.exists && !tp.typeSymbol.is(Final) && !tp.isRef(defn.AnyClass)
         if (templ1.parents.isEmpty &&
             isFullyDefined(pt, ForceDegree.noBottom) &&
             isEligible(pt.underlyingClassRef(refinementOK = false)))