Add use_reflect_codec option

Summary:
An option to tell Thrift-Go generator to use the new reflect codec (implemented downstream).

As is - the diff is no-op.

Reviewed By: leoleovich

Differential Revision: D63473895

fbshipit-source-id: 66d5d630b88b7cd68b4d075ed191fe136e2171cb

thrift/compiler/generate/t_mstch_go_generator.cc

@@ -87,6 +87,8 @@ class mstch_go_program : public mstch_program {
             {"program:gen_metadata?", &mstch_go_program::should_gen_metadata},
             {"program:gen_default_get?",
              &mstch_go_program::should_gen_default_get},
+            {"program:use_reflect_codec?",
+             &mstch_go_program::should_use_reflect_codec},
             {"program:import_metadata_package?",
              &mstch_go_program::should_import_metadata_package},
             {"program:metadata_qualifier",
@@ -127,6 +129,7 @@ class mstch_go_program : public mstch_program {
   }
   mstch::node should_gen_metadata() { return data_.gen_metadata; }
   mstch::node should_gen_default_get() { return data_.gen_default_get; }
+  mstch::node should_use_reflect_codec() { return data_.use_reflect_codec; }
   mstch::node should_import_metadata_package() {
     // We don't need to import the metadata package if we are
     // generating metadata inside the metadata package itself. Duh.
@@ -804,6 +807,9 @@ void t_mstch_go_generator::generate_program() {
   if (auto gen_default_get = get_option("gen_default_get")) {
     data_.gen_default_get = (gen_default_get.value() == "true");
   }
+  if (auto use_reflect_codec = get_option("use_reflect_codec")) {
+    data_.use_reflect_codec = (use_reflect_codec.value() == "true");
+  }
 
   const auto& prog = cached_program(program);
   auto package_dir = std::filesystem::path{

thrift/compiler/lib/go/util.h

@@ -47,6 +47,8 @@ class codegen_data {
   bool gen_metadata = true;
   // whether to generate DefaultGet method
   bool gen_default_get = true;
+  // whether to use reflect codec
+  bool use_reflect_codec = false;
 
   // Records field names for every struct in the program.
   // This is needed to resolve some edge case name collisions.