Do not penalize optional-to-optional conversions when processing the associated value-to-optional conversions. Doing so can result in incorrect ambiguity errors when applying optional-typed arguments to function overload sets with optional and non-optional parameter types. (Hitlisted: rdar://problem/18028526)

Swift SVN r21264

lib/Sema/CSSimplify.cpp

@@ -3401,7 +3401,13 @@ ConstraintSystem::simplifyRestrictedConstraint(ConversionRestrictionKind restric
   //   T $< U ===> T $< U?
   case ConversionRestrictionKind::ValueToOptional: {
     addContextualScore();
-    increaseScore(SK_ValueToOptional);
+    
+    // Do not penalize the conversion if it's really optional-to-optional.
+    if (!(type1->getAnyOptionalObjectType() &&
+          type2->getAnyOptionalObjectType())) {
+      increaseScore(SK_ValueToOptional);
+    }
+    
     assert(matchKind >= TypeMatchKind::Subtype);
     auto generic2 = type2->castTo<BoundGenericType>();
     assert(generic2->getDecl()->classifyAsOptionalType());