Fix but where interface server's transitive superclass's methods weren't…

Fix but where interface server's transitive superclass's methods weren't dispatched correctly -- ouch.

c++/src/capnp/compiler/capnpc-c++.c++

@@ -2131,6 +2131,14 @@ private:
     uint64_t id;
   };
 
+  void getTransitiveSuperclasses(InterfaceSchema schema, std::map<uint64_t, InterfaceSchema>& map) {
+    if (map.insert(std::make_pair(schema.getProto().getId(), schema)).second) {
+      for (auto sup: schema.getSuperclasses()) {
+        getTransitiveSuperclasses(sup, map);
+      }
+    }
+  }
+
   InterfaceText makeInterfaceText(kj::StringPtr scope, kj::StringPtr name, InterfaceSchema schema,
                                   kj::Array<kj::StringTree> nestedTypeDecls,
                                   const TemplateContext& templateContext) {
@@ -2146,6 +2154,16 @@ private:
       return ExtendInfo { cppFullName(superclass, nullptr), superclass.getProto().getId() };
     };
 
+    kj::Array<ExtendInfo> transitiveSuperclasses;
+    {
+      std::map<uint64_t, InterfaceSchema> map;
+      getTransitiveSuperclasses(schema, map);
+      map.erase(schema.getProto().getId());
+      transitiveSuperclasses = KJ_MAP(entry, map) {
+        return ExtendInfo { cppFullName(entry.second, nullptr), entry.second.getProto().getId() };
+      };
+    }
+
     CppTypeName clientName = cppFullName(schema, nullptr);
     clientName.addMemberType("Client");
 
@@ -2305,7 +2323,7 @@ private:
           "  switch (interfaceId) {\n"
           "    case 0x", kj::hex(proto.getId()), "ull:\n"
           "      return dispatchCallInternal(methodId, context);\n",
-          KJ_MAP(s, superclasses) {
+          KJ_MAP(s, transitiveSuperclasses) {
             return kj::strTree(
               "    case 0x", kj::hex(s.id), "ull:\n"
               "      return ", s.typeName, "::Server::dispatchCallInternal(methodId, context);\n");

c++/src/capnp/test-util.h

@@ -210,7 +210,7 @@ private:
   int& callCount;
 };
 
-class TestExtendsImpl final: public test::TestExtends::Server {
+class TestExtendsImpl final: public test::TestExtends2::Server {
 public:
   TestExtendsImpl(int& callCount);
 

c++/src/capnp/test.capnp

@@ -718,6 +718,8 @@ interface TestExtends extends(TestInterface) {
   grault @2 () -> TestAllTypes;
 }
 
+interface TestExtends2 extends(TestExtends) {}
+
 interface TestPipeline {
   getCap @0 (n: UInt32, inCap :TestInterface) -> (s: Text, outBox :Box);
   testPointers @1 (cap :TestInterface, obj :AnyPointer, list :List(TestInterface)) -> ();