Adress reviewers comments

Author: odersky

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

@@ -1331,7 +1331,7 @@ class TypeComparer(initctx: Context) extends DotClass with ConstraintHandling {
           }
           if (homogenizeArgs &&
               isNonvariantAlias(rinfo1) && isNonvariantAlias(rinfo2))
-            isSameType(rinfo1, rinfo2)
+            isSameType(rinfo1, rinfo2) // establish new constraint
 
           tp1.derivedRefinedType(parent, tp1.refinedName, rinfo1 & rinfo2)
         case _ =>

tests/pending/pos/depmet_implicit_oopsla_session_2.scala

@@ -1,4 +1,10 @@
+// Fails on line 70 with: no implicit argument of type Sessions.Session[
+//   |  Sessions.In[Int, Sessions.In[Int, Sessions.Out[Int, Sessions.Stop]]]^
+//   |]#HasDual[Sessions.Out[Int, Sessions.Out[Int, Sessions.In[Int, Sessions.Stop]]]^
+//   |  ] found for parameter evidence$1 of method runSession in object Sessions
+// This could be related to existential types (the # essentially boils down to one).
 object Sessions {
+  def ?[T <: AnyRef](implicit w: T): w.type = w
 
   // session states
   sealed case class Stop()
@@ -17,7 +23,7 @@ object Sessions {
 
   // friendly interface to the theory
   def runSession[S, D: Session[S]#HasDual](session: S, dual: D) =
-    implicitly[Session[S]#HasDual[D]].run(session, dual)
+    ?[Session[S]#HasDual[D]].run(session, dual)
 
   // facts in the theory: