infer singleton when asking for it

a type var's constraint now also tracks whether the type var was
compared to a stable type

if it was, we probably shouldn't widen the type argument that's inferred
for this var, as the result will surely fail to type check

NOTE: must be enabled using -Xexperimental

review by extempore

1 files changed, 3 insertions, 8 deletions

diff --git a/src/compiler/scala/tools/nsc/typechecker/Implicits.scala b/src/compiler/scala/tools/nsc/typechecker/Implicits.scala
index 660999eb64..fedf0a9104 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Implicits.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Implicits.scala
@@ -178,13 +178,8 @@ trait Implicits {
     private val hasMemberCache = perRunCaches.newMap[Name, Type]()
     def apply(name: Name): Type = hasMemberCache.getOrElseUpdate(name, memberWildcardType(name, WildcardType))
     def unapply(pt: Type): Option[Name] = pt match {
-      case RefinedType(List(WildcardType), decls) =>
-        decls.toList match {
-          case List(sym) if sym.tpe == WildcardType => Some(sym.name)
-          case _ => None
-        }
-      case _ =>
-        None
+      case RefinedType(List(WildcardType), Scope(sym)) if sym.tpe == WildcardType => Some(sym.name)
+      case _ => None
     }
   }
 
@@ -570,7 +565,7 @@ trait Implicits {
             // filter out failures from type inference, don't want to remove them from undetParams!
             // we must be conservative in leaving type params in undetparams
             // prototype == WildcardType: want to remove all inferred Nothings
-            val AdjustedTypeArgs(okParams, okArgs) = adjustTypeArgs(undetParams, targs)
+            val AdjustedTypeArgs(okParams, okArgs) = adjustTypeArgs(undetParams, tvars, targs)
             val subst: TreeTypeSubstituter =
               if (okParams.isEmpty) EmptyTreeTypeSubstituter
               else {