Add API to get thrift class name

Summary:
This is needed for using RecursiveEncode with DebugProtocol (otherwise we can't print struct name).

It will be used in the next diff.

Reviewed By: iahs

Differential Revision: D44326880

fbshipit-source-id: 0c46b33f94b0c3d15aa693a05fac6cc88996ba88

thrift/compiler/generate/templates/cpp2/module_data.cpp.mustache

@@ -45,6 +45,7 @@ namespace apache {
 namespace thrift {
 <%#program:structs%>
 
+THRIFT_DATA_MEMBER const folly::StringPiece TStructDataStorage<<%struct:cpp_fullname%>>::name = "<%struct:name%>";
 THRIFT_DATA_MEMBER const std::array<folly::StringPiece, <%struct:fields_size%>> TStructDataStorage<<%struct:cpp_fullname%>>::fields_names = {{
   <%#struct:fields%>
   "<%field:name%>",

thrift/compiler/generate/templates/cpp2/module_data.h.mustache

@@ -62,6 +62,7 @@ template <> struct TEnumDataStorage<<%struct:cpp_fullname%>::Type> {
 
 template <> struct TStructDataStorage<<%struct:cpp_fullname%>> {
   static constexpr const std::size_t fields_size = <%struct:fields_size%>;
+  static const folly::StringPiece name;
   static const std::array<folly::StringPiece, fields_size> fields_names;
   static const std::array<int16_t, fields_size> fields_ids;
   static const std::array<protocol::TType, fields_size> fields_types;

thrift/compiler/generate/templates/cpp2/module_types.cpp.mustache

@@ -116,6 +116,9 @@ const folly::StringPiece <%struct:cpp_underlying_name%>::__fbthrift_get_field_na
   if (ord == ::apache::thrift::FieldOrdinal{0}) { return {}; }
   return apache::thrift::TStructDataStorage<<%struct:cpp_underlying_name%>>::fields_names[folly::to_underlying(ord) - 1];
 }
+const folly::StringPiece <%struct:cpp_underlying_name%>::__fbthrift_get_class_name() {
+  return apache::thrift::TStructDataStorage<<%struct:cpp_underlying_name%>>::name;
+}
 
 <%^struct:union?%>
 <%^struct:cpp_noncopyable%>

thrift/compiler/generate/templates/cpp2/module_types.h.mustache

@@ -105,6 +105,7 @@ class <%#struct:exception?%>FOLLY_EXPORT <%/struct:exception?%><%struct:cpp_unde
   using __fbthrift_patch_struct = <%struct:cpp_underlying_name%>PatchStruct;
   <%/struct:patch?%>
   static const folly::StringPiece __fbthrift_get_field_name(::apache::thrift::FieldOrdinal ord);
+  static const folly::StringPiece __fbthrift_get_class_name();
 <% > module_types_h/reflection%>
 
   void __fbthrift_clear();