Runtime: Update _swift_buildDemanglingForMetadata() for subclass existentials

Author: slavapestov

stdlib/public/runtime/Demangle.cpp

@@ -149,15 +149,42 @@ swift::_swift_buildDemanglingForMetadata(const Metadata *type,
   }
   case MetadataKind::Existential: {
     auto exis = static_cast<const ExistentialTypeMetadata *>(type);
-    NodePointer proto_list = Dem.createNode(Node::Kind::ProtocolList);
-    NodePointer type_list = Dem.createNode(Node::Kind::TypeList);
-
-    proto_list->addChild(type_list, Dem);
+    NodePointer proto_list;
 
     std::vector<const ProtocolDescriptor *> protocols;
     protocols.reserve(exis->Protocols.NumProtocols);
     for (unsigned i = 0, e = exis->Protocols.NumProtocols; i < e; ++i)
       protocols.push_back(exis->Protocols[i]);
+
+    if (exis->getSuperclassConstraint()) {
+      // If there is a superclass constraint, we mangle it specially.
+      proto_list = Dem.createNode(Node::Kind::ProtocolListWithClass);
+    } else if (exis->isClassBounded()) {
+      // Check if the class constraint is implied by any of our
+      // protocols.
+      bool requiresClassImplicit = false;
+
+      for (auto *protocol : protocols) {
+        if (protocol->Flags.getClassConstraint()
+            == ProtocolClassConstraint::Class)
+          requiresClassImplicit = true;
+      }
+
+      // If it was implied, we don't do anything special.
+      if (requiresClassImplicit)
+        proto_list = Dem.createNode(Node::Kind::ProtocolList);
+      // If the existential type has an explicit AnyObject constraint,
+      // we must mangle it as such.
+      else
+        proto_list = Dem.createNode(Node::Kind::ProtocolListWithAnyObject);
+    } else {
+      // Just a simple composition of protocols.
+      proto_list = Dem.createNode(Node::Kind::ProtocolList);
+    }
+
+    NodePointer type_list = Dem.createNode(Node::Kind::TypeList);
+
+    proto_list->addChild(type_list, Dem);
 
     // Sort the protocols by their mangled names.
     // The ordering in the existential type metadata is by metadata pointer,
@@ -198,7 +225,12 @@ swift::_swift_buildDemanglingForMetadata(const Metadata *type,
       assert(protocolNode->getChild(0)->getKind() == Node::Kind::Protocol);
       type_list->addChild(protocolNode, Dem);
     }
-    
+
+    if (auto *superclass = exis->getSuperclassConstraint()) {
+      auto superclassNode = _swift_buildDemanglingForMetadata(superclass, Dem);
+      proto_list->addChild(superclassNode, Dem);
+    }
+
     return proto_list;
   }
   case MetadataKind::ExistentialMetatype: {

test/Interpreter/subclass_existentials.swift

@@ -163,12 +163,10 @@ SubclassExistentialsTestSuite.test("Metadata instantiation") {
 
 // FIXME: Not implemented yet
 
-/*
 SubclassExistentialsTestSuite.test("Metadata to string") {
   expectEqual("Base<Int> & P", String(describing: ((Base<Int>) & P).self))
   expectEqual("Base<Int> & P & Q", String(describing: ((Base<Int>) & P & Q).self))
 }
-*/
 
 SubclassExistentialsTestSuite.test("Call instance methods") {
   do {