Fix problem of overloading resolution when receiver is not stable.

Author: odersky

src/dotty/tools/dotc/core/SymDenotations.scala

@@ -1500,10 +1500,7 @@ object SymDenotations {
         val decls1 = newScope
         for (tparam <- tparams) decls1.enter(decls.lookup(tparam.name))
         for (sym <- decls) if (!typeParams.contains(sym)) decls1.enter(sym)
-        val ci = classInfo
-        // dotty deviation; overloading resolution on next line fails if prefix `ci` is not a value.
-        // See test pending/pos/overloaddefault.scala
-        info = ci.derivedClassInfo(decls = decls1)
+        info = classInfo.derivedClassInfo(decls = decls1)
         myTypeParams = null
       }
 

src/dotty/tools/dotc/transform/Constructors.scala

@@ -246,7 +246,7 @@ class Constructors extends MiniPhaseTransform with SymTransformer { thisTransfor
 
     // Drop accessors that are not retained from class scope
     if (dropped.nonEmpty) {
-      val clsInfo = cls.classInfo // TODO investigate: expand clsInfo to cls.info => dotty type error
+      val clsInfo = cls.classInfo
       cls.copy(
         info = clsInfo.derivedClassInfo(
           decls = clsInfo.decls.filteredScope(!dropped.contains(_))))

src/dotty/tools/dotc/transform/RestoreScopes.scala

@@ -48,9 +48,8 @@ class RestoreScopes extends MiniPhaseTransform with IdentityDenotTransformer { t
     }
 
     pkg.enter(cls)
-    val cinfo = cls.classInfo
     tree.symbol.copySymDenotation(
-      info = cinfo.derivedClassInfo( // Dotty deviation: Cannot expand cinfo inline without a type error
+      info = cls.classInfo.derivedClassInfo(
         decls = restoredDecls: Scope)).installAfter(thisTransform)
     tree
   }

src/dotty/tools/dotc/typer/Applications.scala

@@ -262,8 +262,13 @@ trait Applications extends Compatibility { self: Typer =>
       val receiver: Tree = methPart(normalizedFun) match {
         case Select(receiver, _) => receiver
         case mr => mr.tpe.normalizedPrefix match {
-          case mr: TermRef => ref(mr)
-          case _ => EmptyTree
+          case mr: TermRef =>
+            ref(mr)
+          case mr: TypeRef if this.isInstanceOf[TestApplication[_]] =>
+            // In this case it is safe to skolemize now; we will produce a stable prefix for the actual call.
+            ref(mr.narrow)
+          case _ =>
+            EmptyTree
         }
       }
       val getterPrefix =