[CSBindings] Record holes only after all binding inference steps are done

If there are no direct, transitive or default bindings only then
consider binding the given type variable to a "hole".

Author: xedin

lib/Sema/CSBindings.cpp

@@ -139,6 +139,20 @@ void ConstraintSystem::PotentialBindings::finalize(
         binding.BindingType = OptionalType::get(binding.BindingType);
     }
   }
+
+  // If there are no bindings, typeVar may be a hole.
+  if (cs.shouldAttemptFixes() && Bindings.empty() &&
+      TypeVar->getImpl().canBindToHole()) {
+    IsHole = true;
+    // If the base of the unresolved member reference like `.foo`
+    // couldn't be resolved we'd want to bind it to a hole at the
+    // very last moment possible, just like generic parameters.
+    auto *locator = TypeVar->getImpl().getLocator();
+    if (locator->isLastElement<LocatorPathElt::MemberRefBase>())
+      PotentiallyIncomplete = true;
+
+    addPotentialBinding(PotentialBinding::forHole(cs.getASTContext(), locator));
+  }
 }
 
 Optional<ConstraintSystem::PotentialBindings>
@@ -858,21 +872,6 @@ ConstraintSystem::getPotentialBindings(TypeVariableType *typeVar) const {
     result.addPotentialBinding({type, AllowedBindingKind::Exact, constraint});
   }
 
-  // If there are no bindings, typeVar may be a hole.
-  if (shouldAttemptFixes() && result.Bindings.empty() &&
-      typeVar->getImpl().canBindToHole()) {
-    result.IsHole = true;
-    // If the base of the unresolved member reference like `.foo`
-    // couldn't be resolved we'd want to bind it to a hole at the
-    // very last moment possible, just like generic parameters.
-    auto *locator = typeVar->getImpl().getLocator();
-    if (locator->isLastElement<LocatorPathElt::MemberRefBase>())
-      result.PotentiallyIncomplete = true;
-
-    result.addPotentialBinding(
-        PotentialBinding::forHole(getASTContext(), locator));
-  }
-
   // Determine if the bindings only constrain the type variable from above with
   // an existential type; such a binding is not very helpful because it's
   // impossible to enumerate the existential type's subtypes.