Update superCallContext to include dummy capture parameters in scope

Author: noti0na1

compiler/src/dotty/tools/dotc/core/Contexts.scala

@@ -402,8 +402,8 @@ object Contexts {
      *
      *  - as owner: The primary constructor of the class
      *  - as outer context: The context enclosing the class context
-     *  - as scope: type parameters, the parameter accessors, and
-     *    the context bound companions in the class context,
+     *  - as scope: type parameters, the parameter accessors,
+     *    the dummy capture parameters and the context bound companions in the class context,
      *
      *  The reasons for this peculiar choice of attributes are as follows:
      *
@@ -420,7 +420,7 @@ object Contexts {
     def superCallContext: Context =
       val locals = owner.typeParams
           ++ owner.asClass.unforcedDecls.filter: sym =>
-              sym.is(ParamAccessor) || sym.isContextBoundCompanion
+              sym.is(ParamAccessor) || sym.isContextBoundCompanion || sym.isDummyCaptureParam
       superOrThisCallContext(owner.primaryConstructor, newScopeWith(locals*))
 
     /** The context for the arguments of a this(...) constructor call.

tests/pos-custom-args/captures/i23737.scala

@@ -0,0 +1,10 @@
+import language.experimental.captureChecking
+
+class C
+
+trait A[T]
+
+trait B[CC^] extends A[C^{CC}] // error: CC not found
+
+trait D[CC^]:
+  val x: Object^{CC} = ???