Fine-tuning of isRepresentableWithWildcards and wildcard printing.

2 files changed, 22 insertions, 21 deletions

diff --git a/src/compiler/scala/reflect/internal/Types.scala b/src/compiler/scala/reflect/internal/Types.scala
index c13a33a6fc..b3d425f0c5 100644
--- a/src/compiler/scala/reflect/internal/Types.scala
+++ b/src/compiler/scala/reflect/internal/Types.scala
@@ -2517,34 +2517,35 @@ trait Types extends api.Types { self: SymbolTable =>
     override def skolemizeExistential(owner: Symbol, origin: AnyRef) =
       deriveType(quantified, tparam => (owner orElse tparam.owner).newExistentialSkolem(tparam, origin))(underlying)
 
-    private def wildcardArgsString(available: Set[Symbol], args: List[Type]): List[String] = args match {
-      case TypeRef(_, sym, _) :: args1 if (available contains sym) =>
-        ("_"+sym.infoString(sym.info)) :: wildcardArgsString(available - sym, args1)
-      case arg :: args1 if !(quantified exists (arg contains _)) =>
-        arg.toString :: wildcardArgsString(available, args1)
-      case _ =>
-        List()
+    private def wildcardArgsString(qset: Set[Symbol], args: List[Type]): List[String] = args map {
+      case TypeRef(_, sym, _) if (qset contains sym) =>
+        "_"+sym.infoString(sym.info)
+      case arg =>
+        arg.toString
     }
+
     /** An existential can only be printed with wildcards if:
      *   - the underlying type is a typeref
-     *   - where there is a 1-to-1 correspondence between underlying's typeargs and quantified
-     *   - and none of the existential parameters is referenced from anywhere else in the type
-     *   - and none of the existential parameters are singleton types
-     *   - @param checkBounds  if set returns false for situations like
-     *                         (S, T) forSome { type S; type T <: S }
-     *                         If not set returns true. The reason for this mode is to
-     *                         avoid cyclic reference errors when the method is called
-     *                         early (e.g. from Typers # checkExistentialsFeature)
+     *   - every quantified variable appears at most once as a type argument and
+     *     nowhere inside a type argument
+     *   - no quantified type argument contains a quantified variable in its bound
+     *   - the typeref's symbol is not itself quantified
+     *   - the prefix is not quanitified
      */
-    def isRepresentableWithWildcards(checkBounds: Boolean) = {
+    def isRepresentableWithWildcards = {
       val qset = quantified.toSet
       underlying match {
-        case TypeRef(_, sym, args) =>
-          def isQuantified(tpe: Type) = tpe exists (t => quantified contains t.typeSymbol)
+        case TypeRef(pre, sym, args) =>
+          def isQuantified(tpe: Type): Boolean = {
+            (tpe exists (t => qset contains t.typeSymbol)) ||
+            tpe.typeSymbol.isRefinementClass && (tpe.parents exists isQuantified)
+          }
           val (wildcardArgs, otherArgs) = args partition (arg => qset contains arg.typeSymbol)
           wildcardArgs.distinct == wildcardArgs &&
           !(otherArgs exists (arg => isQuantified(arg))) &&
-          !(wildcardArgs exists (arg => isQuantified(arg.typeSymbol.info.bounds)))
+          !(wildcardArgs exists (arg => isQuantified(arg.typeSymbol.info.bounds))) &&
+          !(qset contains sym) &&
+          !isQuantified(pre)
         case _ => false
       }
     }
@@ -2555,7 +2556,7 @@ trait Types extends api.Types { self: SymbolTable =>
         if (settings.explaintypes.value) "(" + str + ")" else str
       }
       underlying match {
-        case TypeRef(pre, sym, args) if !settings.debug.value && isRepresentableWithWildcards(checkBounds = true) =>
+        case TypeRef(pre, sym, args) if !settings.debug.value && isRepresentableWithWildcards =>
           "" + TypeRef(pre, sym, Nil) + wildcardArgsString(quantified.toSet, args).mkString("[", ", ", "]")
         case MethodType(_, _) | NullaryMethodType(_) | PolyType(_, _) =>
           "(" + underlying + ")" + clauses
diff --git a/src/compiler/scala/tools/nsc/typechecker/Typers.scala b/src/compiler/scala/tools/nsc/typechecker/Typers.scala
index 1425cd4755..9431c6f5e5 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Typers.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Typers.scala
@@ -761,7 +761,7 @@ trait Typers extends Modes with Adaptations with PatMatVirtualiser {
       }
 
     def checkExistentialsFeature(pos: Position, tpe: Type, prefix: String) = tpe match {
-      case extp: ExistentialType if !extp.isRepresentableWithWildcards(checkBounds = false) =>
+      case extp: ExistentialType if !extp.isRepresentableWithWildcards =>
         checkFeature(pos, ExistentialsFeature, prefix+" "+tpe)
       case _ =>
     }