pure-Ruby DSL is passing all tests!
diff --git a/ruby/Rakefile b/ruby/Rakefile
index 221e9b5..523d4de 100644
--- a/ruby/Rakefile
+++ b/ruby/Rakefile
@@ -8,6 +8,7 @@
 well_known_protos = %w[
   google/protobuf/any.proto
   google/protobuf/api.proto
+  google/protobuf/descriptor.proto
   google/protobuf/duration.proto
   google/protobuf/empty.proto
   google/protobuf/field_mask.proto
diff --git a/ruby/ext/google/protobuf_c/defs.c b/ruby/ext/google/protobuf_c/defs.c
index 88da610..fd32cce 100644
--- a/ruby/ext/google/protobuf_c/defs.c
+++ b/ruby/ext/google/protobuf_c/defs.c
@@ -36,13 +36,6 @@
 #include "message.h"
 #include "protobuf.h"
 
-static VALUE Builder_build(VALUE _self);
-
-static VALUE cMessageBuilderContext;
-static VALUE cOneofBuilderContext;
-static VALUE cEnumBuilderContext;
-static VALUE cBuilder;
-
 // -----------------------------------------------------------------------------
 // Global map from upb {msg,enum}defs to wrapper Descriptor/EnumDescriptor
 // instances.
@@ -76,167 +69,6 @@
 }
 
 // -----------------------------------------------------------------------------
-// Backward compatibility code.
-// -----------------------------------------------------------------------------
-
-static void rewrite_enum_default(const upb_symtab* symtab,
-                                 google_protobuf_FileDescriptorProto* file,
-                                 google_protobuf_FieldDescriptorProto* field) {
-  upb_strview defaultval;
-  const char *type_name_str;
-  char *end;
-  long val;
-  const upb_enumdef *e;
-  upb_strview type_name;
-
-  /* Look for TYPE_ENUM fields that have a default. */
-  if (google_protobuf_FieldDescriptorProto_type(field) !=
-          google_protobuf_FieldDescriptorProto_TYPE_ENUM ||
-      !google_protobuf_FieldDescriptorProto_has_default_value(field) ||
-      !google_protobuf_FieldDescriptorProto_has_type_name(field)) {
-    return;
-  }
-
-  defaultval = google_protobuf_FieldDescriptorProto_default_value(field);
-  type_name = google_protobuf_FieldDescriptorProto_type_name(field);
-
-  if (defaultval.size == 0 || !isdigit(defaultval.data[0])) {
-    return;
-  }
-
-  if (type_name.size == 0 || type_name.data[0] != '.') {
-    return;
-  }
-
-  type_name_str = type_name.data + 1;
-
-  errno = 0;
-  val = strtol(defaultval.data, &end, 10);
-
-  if (errno != 0 || *end != 0 || val < INT32_MIN || val > INT32_MAX) {
-    return;
-  }
-
-  /* Now find the corresponding enum definition. */
-  e = upb_symtab_lookupenum(symtab, type_name_str);
-  if (e) {
-    /* Look in previously loaded files. */
-    const char *label = upb_enumdef_iton(e, val);
-    if (!label) {
-      return;
-    }
-    google_protobuf_FieldDescriptorProto_set_default_value(
-        field, upb_strview_makez(label));
-  } else {
-    /* Look in enums defined in this file. */
-    const google_protobuf_EnumDescriptorProto* matching_enum = NULL;
-    size_t i, n;
-    const google_protobuf_EnumDescriptorProto* const* enums =
-        google_protobuf_FileDescriptorProto_enum_type(file, &n);
-    const google_protobuf_EnumValueDescriptorProto* const* values;
-
-    for (i = 0; i < n; i++) {
-      if (upb_strview_eql(google_protobuf_EnumDescriptorProto_name(enums[i]),
-                          upb_strview_makez(type_name_str))) {
-        matching_enum = enums[i];
-        break;
-      }
-    }
-
-    if (!matching_enum) {
-      return;
-    }
-
-    values = google_protobuf_EnumDescriptorProto_value(matching_enum, &n);
-    for (i = 0; i < n; i++) {
-      if (google_protobuf_EnumValueDescriptorProto_number(values[i]) == val) {
-        google_protobuf_FieldDescriptorProto_set_default_value(
-            field, google_protobuf_EnumValueDescriptorProto_name(values[i]));
-        return;
-      }
-    }
-
-    /* We failed to find an enum default.  But we'll just leave the enum
-     * untouched and let the normal def-building code catch it. */
-  }
-}
-
-/* Historically we allowed enum defaults to be specified as a number.  In
- * retrospect this was a mistake as descriptors require defaults to be
- * specified as a label. This can make a difference if multiple labels have the
- * same number.
- *
- * Here we do a pass over all enum defaults and rewrite numeric defaults by
- * looking up their labels.  This is complicated by the fact that the enum
- * definition can live in either the symtab or the file_proto.
- * */
-static void rewrite_enum_defaults(
-    const upb_symtab* symtab, google_protobuf_FileDescriptorProto* file_proto) {
-  size_t i, n;
-  google_protobuf_DescriptorProto** msgs =
-      google_protobuf_FileDescriptorProto_mutable_message_type(file_proto, &n);
-
-  for (i = 0; i < n; i++) {
-    size_t j, m;
-    google_protobuf_FieldDescriptorProto** fields =
-        google_protobuf_DescriptorProto_mutable_field(msgs[i], &m);
-    for (j = 0; j < m; j++) {
-      rewrite_enum_default(symtab, file_proto, fields[j]);
-    }
-  }
-}
-
-static void remove_path(upb_strview *name) {
-  const char* last = strrchr(name->data, '.');
-  if (last) {
-    size_t remove = last - name->data + 1;
-    name->data += remove;
-    name->size -= remove;
-  }
-}
-
-static void rewrite_nesting(VALUE msg_ent, google_protobuf_DescriptorProto* msg,
-                            google_protobuf_DescriptorProto* const* msgs,
-                            google_protobuf_EnumDescriptorProto* const* enums,
-                            upb_arena *arena) {
-  VALUE submsgs = rb_hash_aref(msg_ent, ID2SYM(rb_intern("msgs")));
-  VALUE enum_pos = rb_hash_aref(msg_ent, ID2SYM(rb_intern("enums")));
-  int submsg_count;
-  int enum_count;
-  int i;
-  google_protobuf_DescriptorProto** msg_msgs;
-  google_protobuf_EnumDescriptorProto** msg_enums;
-
-  Check_Type(submsgs, T_ARRAY);
-  Check_Type(enum_pos, T_ARRAY);
-
-  submsg_count = RARRAY_LEN(submsgs);
-  enum_count = RARRAY_LEN(enum_pos);
-
-  msg_msgs = google_protobuf_DescriptorProto_resize_nested_type(
-      msg, submsg_count, arena);
-  msg_enums =
-      google_protobuf_DescriptorProto_resize_enum_type(msg, enum_count, arena);
-
-  for (i = 0; i < submsg_count; i++) {
-    VALUE submsg_ent = RARRAY_PTR(submsgs)[i];
-    VALUE pos = rb_hash_aref(submsg_ent, ID2SYM(rb_intern("pos")));
-    upb_strview name;
-
-    msg_msgs[i] = msgs[NUM2INT(pos)];
-    name = google_protobuf_DescriptorProto_name(msg_msgs[i]);
-    remove_path(&name);
-    google_protobuf_DescriptorProto_set_name(msg_msgs[i], name);
-    rewrite_nesting(submsg_ent, msg_msgs[i], msgs, enums, arena);
-  }
-
-  for (i = 0; i < enum_count; i++) {
-    VALUE pos = RARRAY_PTR(enum_pos)[i];
-    msg_enums[i] = enums[NUM2INT(pos)];
-  }
-}
-
-// -----------------------------------------------------------------------------
 // DescriptorPool.
 // -----------------------------------------------------------------------------
 
@@ -302,43 +134,32 @@
 
 /*
  * call-seq:
- *     DescriptorPool.build(&block)
- *
- * Invokes the block with a Builder instance as self. All message and enum types
- * added within the block are committed to the pool atomically, and may refer
- * (co)recursively to each other. The user should call Builder#add_message and
- * Builder#add_enum within the block as appropriate.  This is the recommended,
- * idiomatic way to define new message and enum types.
- */
-static VALUE DescriptorPool_build(int argc, VALUE* argv, VALUE _self) {
-  VALUE ctx = rb_class_new_instance(1, &_self, cBuilder);
-  VALUE block = rb_block_proc();
-  rb_funcall_with_block(ctx, rb_intern("instance_eval"), 0, NULL, block);
-  Builder_build(ctx);
-  return Qnil;
-}
-
-/*
- * call-seq:
- *     DescriptorPool.build_file(serialized_file_proto)
+ *     DescriptorPool.add_serialized_file(serialized_file_proto)
  *
  * Adds the given serialized FileDescriptorProto to the pool.
  */
-VALUE DescriptorPool_build(value _self, VALUE serialized_file_proto) {
-  DEFINE_SELF(DescriptorPool, self, _self);
+VALUE DescriptorPool_add_serialized_file(VALUE _self,
+                                         VALUE serialized_file_proto) {
+  DescriptorPool* self = ruby_to_DescriptorPool(_self);
   Check_Type(serialized_file_proto, T_STRING);
-  upb_arena *arena = upb_arena_new();
+  VALUE arena_rb = Arena_new();
+  upb_arena *arena = Arena_get(arena_rb);
   google_protobuf_FileDescriptorProto* file_proto =
       google_protobuf_FileDescriptorProto_parse(
           RSTRING_PTR(serialized_file_proto),
           RSTRING_LEN(serialized_file_proto), arena);
+  if (!file_proto) {
+    rb_raise(rb_eArgError, "Unable to parse FileDescriptorProto");
+  }
   upb_status status;
   upb_status_clear(&status);
-  if (!upb_symtab_addfile(self->symtab, file_proto, &status)) {
+  const upb_filedef* filedef =
+      upb_symtab_addfile(self->symtab, file_proto, &status);
+  if (!filedef) {
     rb_raise(cTypeError, "Unable to build file to DescriptorPool: %s",
              upb_status_errmsg(&status));
   }
-  return Qnil;
+  return get_filedef_obj(_self, filedef);
 }
 
 /*
@@ -384,7 +205,8 @@
   VALUE klass = rb_define_class_under(
       module, "DescriptorPool", rb_cObject);
   rb_define_alloc_func(klass, DescriptorPool_alloc);
-  rb_define_method(klass, "build", DescriptorPool_build, -1);
+  rb_define_method(klass, "add_serialized_file",
+                   DescriptorPool_add_serialized_file, 1);
   rb_define_method(klass, "lookup", DescriptorPool_lookup, 1);
   rb_define_singleton_method(klass, "generated_pool",
                              DescriptorPool_generated_pool, 0);
@@ -796,41 +618,6 @@
   return 0;
 }
 
-static upb_descriptortype_t ruby_to_descriptortype(VALUE type) {
-  if (TYPE(type) != T_SYMBOL) {
-    rb_raise(rb_eArgError, "Expected symbol for field type.");
-  }
-
-#define CONVERT(upb, ruby)                                           \
-  if (SYM2ID(type) == rb_intern( # ruby )) {                         \
-    return UPB_DESCRIPTOR_TYPE_ ## upb;                              \
-  }
-
-  CONVERT(FLOAT, float);
-  CONVERT(DOUBLE, double);
-  CONVERT(BOOL, bool);
-  CONVERT(STRING, string);
-  CONVERT(BYTES, bytes);
-  CONVERT(MESSAGE, message);
-  CONVERT(GROUP, group);
-  CONVERT(ENUM, enum);
-  CONVERT(INT32, int32);
-  CONVERT(INT64, int64);
-  CONVERT(UINT32, uint32);
-  CONVERT(UINT64, uint64);
-  CONVERT(SINT32, sint32);
-  CONVERT(SINT64, sint64);
-  CONVERT(FIXED32, fixed32);
-  CONVERT(FIXED64, fixed64);
-  CONVERT(SFIXED32, sfixed32);
-  CONVERT(SFIXED64, sfixed64);
-
-#undef CONVERT
-
-  rb_raise(rb_eArgError, "Unknown field type.");
-  return 0;
-}
-
 static VALUE descriptortype_to_ruby(upb_descriptortype_t type) {
   switch (type) {
 #define CONVERT(upb, ruby)                                           \
@@ -1376,1117 +1163,6 @@
   cEnumDescriptor = klass;
 }
 
-// -----------------------------------------------------------------------------
-// FileBuilderContext.
-// -----------------------------------------------------------------------------
-
-typedef struct {
-  upb_arena *arena;
-  google_protobuf_FileDescriptorProto* file_proto;
-  VALUE descriptor_pool;
-} FileBuilderContext;
-
-static VALUE cFileBuilderContext = Qnil;
-
-static void FileBuilderContext_mark(void* _self) {
-  FileBuilderContext* self = _self;
-  rb_gc_mark(self->descriptor_pool);
-}
-
-static void FileBuilderContext_free(void* _self) {
-  FileBuilderContext* self = _self;
-  upb_arena_free(self->arena);
-  xfree(self);
-}
-
-static const rb_data_type_t FileBuilderContext_type = {
-  "Google::Protobuf::Internal::FileBuilderContext",
-  {FileBuilderContext_mark, FileBuilderContext_free, NULL},
-  .flags = RUBY_TYPED_FREE_IMMEDIATELY,
-};
-
-static FileBuilderContext* ruby_to_FileBuilderContext(VALUE val) {
-  FileBuilderContext* ret;
-  TypedData_Get_Struct(val, FileBuilderContext, &FileBuilderContext_type, ret);
-  return ret;
-}
-
-static upb_strview FileBuilderContext_strdup2(VALUE _self, const char *str) {
-  FileBuilderContext* self = ruby_to_FileBuilderContext(_self);
-  upb_strview ret;
-  char *data;
-
-  ret.size = strlen(str);
-  data = upb_malloc(upb_arena_alloc(self->arena), ret.size + 1);
-  ret.data = data;
-  memcpy(data, str, ret.size);
-  /* Null-terminate required by rewrite_enum_defaults() above. */
-  data[ret.size] = '\0';
-  return ret;
-}
-
-static upb_strview FileBuilderContext_strdup(VALUE _self, VALUE rb_str) {
-  return FileBuilderContext_strdup2(_self, get_str(rb_str));
-}
-
-static upb_strview FileBuilderContext_strdup_sym(VALUE _self, VALUE rb_sym) {
-  Check_Type(rb_sym, T_SYMBOL);
-  return FileBuilderContext_strdup(_self, rb_id2str(SYM2ID(rb_sym)));
-}
-
-static VALUE FileBuilderContext_alloc(VALUE klass) {
-  FileBuilderContext* self = ALLOC(FileBuilderContext);
-  VALUE ret = TypedData_Wrap_Struct(klass, &FileBuilderContext_type, self);
-  self->arena = upb_arena_new();
-  self->file_proto = google_protobuf_FileDescriptorProto_new(self->arena);
-  self->descriptor_pool = Qnil;
-  return ret;
-}
-
-/*
- * call-seq:
- *     FileBuilderContext.new(descriptor_pool) => context
- *
- * Create a new file builder context for the given file descriptor and
- * builder context. This class is intended to serve as a DSL context to be used
- * with #instance_eval.
- */
-static VALUE FileBuilderContext_initialize(VALUE _self, VALUE descriptor_pool,
-                                           VALUE name, VALUE options) {
-  FileBuilderContext* self = ruby_to_FileBuilderContext(_self);
-  self->descriptor_pool = descriptor_pool;
-
-  google_protobuf_FileDescriptorProto_set_name(
-      self->file_proto, FileBuilderContext_strdup(_self, name));
-
-  // Default syntax for Ruby is proto3.
-  google_protobuf_FileDescriptorProto_set_syntax(
-      self->file_proto,
-      FileBuilderContext_strdup(_self, rb_str_new2("proto3")));
-
-  if (options != Qnil) {
-    VALUE syntax;
-
-    Check_Type(options, T_HASH);
-    syntax = rb_hash_lookup2(options, ID2SYM(rb_intern("syntax")), Qnil);
-
-    if (syntax != Qnil) {
-      VALUE syntax_str;
-
-      Check_Type(syntax, T_SYMBOL);
-      syntax_str = rb_id2str(SYM2ID(syntax));
-      google_protobuf_FileDescriptorProto_set_syntax(
-          self->file_proto, FileBuilderContext_strdup(_self, syntax_str));
-    }
-  }
-
-  return Qnil;
-}
-
-<<<<<<< HEAD
-static VALUE make_mapentry(VALUE _message_builder, VALUE types, int argc,
-                           const VALUE* argv) {
-  DEFINE_SELF(MessageBuilderContext, message_builder, _message_builder);
-=======
-static void MessageBuilderContext_add_synthetic_oneofs(VALUE _self);
-
-/*
- * call-seq:
- *     FileBuilderContext.add_message(name, &block)
- *
- * Creates a new, empty descriptor with the given name, and invokes the block in
- * the context of a MessageBuilderContext on that descriptor. The block can then
- * call, e.g., MessageBuilderContext#optional and MessageBuilderContext#repeated
- * methods to define the message fields.
- *
- * This is the recommended, idiomatic way to build message definitions.
- */
-static VALUE FileBuilderContext_add_message(VALUE _self, VALUE name) {
-  VALUE args[2] = { _self, name };
-  VALUE ctx = rb_class_new_instance(2, args, cMessageBuilderContext);
-  VALUE block = rb_block_proc();
-  rb_funcall_with_block(ctx, rb_intern("instance_eval"), 0, NULL, block);
-  MessageBuilderContext_add_synthetic_oneofs(ctx);
-  return Qnil;
-}
-
-/* We have to do some relatively complicated logic here for backward
- * compatibility.
- *
- * In descriptor.proto, messages are nested inside other messages if that is
- * what the original .proto file looks like.  For example, suppose we have this
- * foo.proto:
- *
- * package foo;
- * message Bar {
- *   message Baz {}
- * }
- *
- * The descriptor for this must look like this:
- *
- * file {
- *   name: "test.proto"
- *   package: "foo"
- *   message_type {
- *     name: "Bar"
- *     nested_type {
- *       name: "Baz"
- *     }
- *   }
- * }
- *
- * However, the Ruby generated code has always generated messages in a flat,
- * non-nested way:
- *
- * Google::Protobuf::DescriptorPool.generated_pool.build do
- *   add_message "foo.Bar" do
- *   end
- *   add_message "foo.Bar.Baz" do
- *   end
- * end
- *
- * Here we need to do a translation where we turn this generated code into the
- * above descriptor.  We need to infer that "foo" is the package name, and not
- * a message itself.
- *
- * We delegate to Ruby to compute the transformation, for more concice and
- * readable code than we can do in C */
-static void rewrite_names(VALUE _file_builder,
-                          google_protobuf_FileDescriptorProto* file_proto) {
-  FileBuilderContext* file_builder = ruby_to_FileBuilderContext(_file_builder);
-  upb_arena *arena = file_builder->arena;
-  // Build params (package, msg_names, enum_names).
-  VALUE package = Qnil;
-  VALUE msg_names = rb_ary_new();
-  VALUE enum_names = rb_ary_new();
-  size_t msg_count, enum_count, i;
-  VALUE new_package, nesting, msg_ents, enum_ents;
-  google_protobuf_DescriptorProto** msgs;
-  google_protobuf_EnumDescriptorProto** enums;
-
-  if (google_protobuf_FileDescriptorProto_has_package(file_proto)) {
-    upb_strview package_str =
-        google_protobuf_FileDescriptorProto_package(file_proto);
-    package = rb_str_new(package_str.data, package_str.size);
-  }
-
-  msgs = google_protobuf_FileDescriptorProto_mutable_message_type(file_proto,
-                                                                  &msg_count);
-  for (i = 0; i < msg_count; i++) {
-    upb_strview name = google_protobuf_DescriptorProto_name(msgs[i]);
-    rb_ary_push(msg_names, rb_str_new(name.data, name.size));
-  }
-
-  enums = google_protobuf_FileDescriptorProto_mutable_enum_type(file_proto,
-                                                                &enum_count);
-  for (i = 0; i < enum_count; i++) {
-    upb_strview name = google_protobuf_EnumDescriptorProto_name(enums[i]);
-    rb_ary_push(enum_names, rb_str_new(name.data, name.size));
-  }
-
-  {
-    // Call Ruby code to calculate package name and nesting.
-    VALUE args[3] = { package, msg_names, enum_names };
-    VALUE internal = rb_eval_string("Google::Protobuf::Internal");
-    VALUE ret = rb_funcallv(internal, rb_intern("fixup_descriptor"), 3, args);
-
-    new_package = rb_ary_entry(ret, 0);
-    nesting = rb_ary_entry(ret, 1);
-  }
-
-  // Rewrite package and names.
-  if (new_package != Qnil) {
-    upb_strview new_package_str =
-        FileBuilderContext_strdup(_file_builder, new_package);
-    google_protobuf_FileDescriptorProto_set_package(file_proto,
-                                                    new_package_str);
-  }
-
-  for (i = 0; i < msg_count; i++) {
-    upb_strview name = google_protobuf_DescriptorProto_name(msgs[i]);
-    remove_path(&name);
-    google_protobuf_DescriptorProto_set_name(msgs[i], name);
-  }
-
-  for (i = 0; i < enum_count; i++) {
-    upb_strview name = google_protobuf_EnumDescriptorProto_name(enums[i]);
-    remove_path(&name);
-    google_protobuf_EnumDescriptorProto_set_name(enums[i], name);
-  }
-
-  // Rewrite nesting.
-  msg_ents = rb_hash_aref(nesting, ID2SYM(rb_intern("msgs")));
-  enum_ents = rb_hash_aref(nesting, ID2SYM(rb_intern("enums")));
-
-  Check_Type(msg_ents, T_ARRAY);
-  Check_Type(enum_ents, T_ARRAY);
-
-  for (i = 0; i < (size_t)RARRAY_LEN(msg_ents); i++) {
-    VALUE msg_ent = rb_ary_entry(msg_ents, i);
-    VALUE pos = rb_hash_aref(msg_ent, ID2SYM(rb_intern("pos")));
-    msgs[i] = msgs[NUM2INT(pos)];
-    rewrite_nesting(msg_ent, msgs[i], msgs, enums, arena);
-  }
-
-  for (i = 0; i < (size_t)RARRAY_LEN(enum_ents); i++) {
-    VALUE enum_pos = rb_ary_entry(enum_ents, i);
-    enums[i] = enums[NUM2INT(enum_pos)];
-  }
-
-  google_protobuf_FileDescriptorProto_resize_message_type(
-      file_proto, RARRAY_LEN(msg_ents), arena);
-  google_protobuf_FileDescriptorProto_resize_enum_type(
-      file_proto, RARRAY_LEN(enum_ents), arena);
-}
-
-/*
- * call-seq:
- *     FileBuilderContext.add_enum(name, &block)
- *
- * Creates a new, empty enum descriptor with the given name, and invokes the
- * block in the context of an EnumBuilderContext on that descriptor. The block
- * can then call EnumBuilderContext#add_value to define the enum values.
- *
- * This is the recommended, idiomatic way to build enum definitions.
- */
-static VALUE FileBuilderContext_add_enum(VALUE _self, VALUE name) {
-  VALUE args[2] = { _self, name };
-  VALUE ctx = rb_class_new_instance(2, args, cEnumBuilderContext);
-  VALUE block = rb_block_proc();
-  rb_funcall_with_block(ctx, rb_intern("instance_eval"), 0, NULL, block);
-  return Qnil;
-}
-
-static void FileBuilderContext_build(VALUE _self) {
-  FileBuilderContext* self = ruby_to_FileBuilderContext(_self);
-  DescriptorPool* pool = ruby_to_DescriptorPool(self->descriptor_pool);
-  upb_status status;
-
-  rewrite_enum_defaults(pool->symtab, self->file_proto);
-  rewrite_names(_self, self->file_proto);
-
-  upb_status_clear(&status);
-  if (!upb_symtab_addfile(pool->symtab, self->file_proto, &status)) {
-    rb_raise(cTypeError, "Unable to add defs to DescriptorPool: %s",
-             upb_status_errmsg(&status));
-  }
-}
-
-static void FileBuilderContext_register(VALUE module) {
-  VALUE klass = rb_define_class_under(module, "FileBuilderContext", rb_cObject);
-  rb_define_alloc_func(klass, FileBuilderContext_alloc);
-  rb_define_method(klass, "initialize", FileBuilderContext_initialize, 3);
-  rb_define_method(klass, "add_message", FileBuilderContext_add_message, 1);
-  rb_define_method(klass, "add_enum", FileBuilderContext_add_enum, 1);
-  rb_gc_register_address(&cFileBuilderContext);
-  cFileBuilderContext = klass;
-}
-
-// -----------------------------------------------------------------------------
-// MessageBuilderContext.
-// -----------------------------------------------------------------------------
-
-typedef struct {
-  google_protobuf_DescriptorProto* msg_proto;
-  VALUE file_builder;
-} MessageBuilderContext;
-
-static VALUE cMessageBuilderContext = Qnil;
-
-static void MessageBuilderContext_mark(void* _self) {
-  MessageBuilderContext* self = _self;
-  rb_gc_mark(self->file_builder);
-}
-
-static const rb_data_type_t MessageBuilderContext_type = {
-  "Google::Protobuf::Internal::MessageBuilderContext",
-  {MessageBuilderContext_mark, RUBY_DEFAULT_FREE, NULL},
-  .flags = RUBY_TYPED_FREE_IMMEDIATELY,
-};
-
-static MessageBuilderContext* ruby_to_MessageBuilderContext(VALUE val) {
-  MessageBuilderContext* ret;
-  TypedData_Get_Struct(val, MessageBuilderContext, &MessageBuilderContext_type,
-                       ret);
-  return ret;
-}
-
-static VALUE MessageBuilderContext_alloc(VALUE klass) {
-  MessageBuilderContext* self = ALLOC(MessageBuilderContext);
-  VALUE ret = TypedData_Wrap_Struct(klass, &MessageBuilderContext_type, self);
-  self->file_builder = Qnil;
-  return ret;
-}
-
-/*
- * call-seq:
- *     MessageBuilderContext.new(file_builder, name) => context
- *
- * Create a new message builder context around the given message descriptor and
- * builder context. This class is intended to serve as a DSL context to be used
- * with #instance_eval.
- */
-static VALUE MessageBuilderContext_initialize(VALUE _self, VALUE _file_builder,
-                                              VALUE name) {
-  MessageBuilderContext* self = ruby_to_MessageBuilderContext(_self);
-  FileBuilderContext* file_builder = ruby_to_FileBuilderContext(_file_builder);
-  google_protobuf_FileDescriptorProto* file_proto = file_builder->file_proto;
-
-  self->file_builder = _file_builder;
-  self->msg_proto = google_protobuf_FileDescriptorProto_add_message_type(
-      file_proto, file_builder->arena);
-
-  google_protobuf_DescriptorProto_set_name(
-      self->msg_proto, FileBuilderContext_strdup(_file_builder, name));
-
-  return Qnil;
-}
-
-static void msgdef_add_field(VALUE msgbuilder_rb, upb_label_t label, VALUE name,
-                             VALUE type, VALUE number, VALUE type_class,
-                             VALUE options, int oneof_index,
-                             bool proto3_optional) {
-  MessageBuilderContext* self = ruby_to_MessageBuilderContext(msgbuilder_rb);
-  FileBuilderContext* file_context =
-      ruby_to_FileBuilderContext(self->file_builder);
-  google_protobuf_FieldDescriptorProto* field_proto;
-  VALUE name_str;
-
-  field_proto = google_protobuf_DescriptorProto_add_field(self->msg_proto,
-                                                          file_context->arena);
-
-  Check_Type(name, T_SYMBOL);
-  name_str = rb_id2str(SYM2ID(name));
-
-  google_protobuf_FieldDescriptorProto_set_name(
-      field_proto, FileBuilderContext_strdup(self->file_builder, name_str));
-  google_protobuf_FieldDescriptorProto_set_number(field_proto, NUM2INT(number));
-  google_protobuf_FieldDescriptorProto_set_label(field_proto, (int)label);
-  google_protobuf_FieldDescriptorProto_set_type(
-      field_proto, (int)ruby_to_descriptortype(type));
-
-  if (proto3_optional) {
-    google_protobuf_FieldDescriptorProto_set_proto3_optional(field_proto, true);
-  }
-
-  if (type_class != Qnil) {
-    Check_Type(type_class, T_STRING);
-
-    // Make it an absolute type name by prepending a dot.
-    type_class = rb_str_append(rb_str_new2("."), type_class);
-    google_protobuf_FieldDescriptorProto_set_type_name(
-        field_proto, FileBuilderContext_strdup(self->file_builder, type_class));
-  }
-
-  if (options != Qnil) {
-    Check_Type(options, T_HASH);
-
-    if (rb_funcall(options, rb_intern("key?"), 1,
-                   ID2SYM(rb_intern("default"))) == Qtrue) {
-      VALUE default_value =
-          rb_hash_lookup(options, ID2SYM(rb_intern("default")));
-
-      /* Call #to_s since all defaults are strings in the descriptor. */
-      default_value = rb_funcall(default_value, rb_intern("to_s"), 0);
-
-      google_protobuf_FieldDescriptorProto_set_default_value(
-          field_proto,
-          FileBuilderContext_strdup(self->file_builder, default_value));
-    }
-
-    if (rb_funcall(options, rb_intern("key?"), 1,
-                   ID2SYM(rb_intern("json_name"))) == Qtrue) {
-      VALUE json_name =
-          rb_hash_lookup(options, ID2SYM(rb_intern("json_name")));
-
-      google_protobuf_FieldDescriptorProto_set_json_name(
-          field_proto,
-          FileBuilderContext_strdup(self->file_builder, json_name));
-    }
-  }
-
-  if (oneof_index >= 0) {
-    google_protobuf_FieldDescriptorProto_set_oneof_index(field_proto,
-                                                         oneof_index);
-  }
-}
-
-#if RUBY_API_VERSION_CODE >= 20700
-static VALUE make_mapentry(VALUE _message_builder, VALUE types, int argc,
-                           const VALUE* argv, VALUE blockarg) {
-  (void)blockarg;
-#else
-static VALUE make_mapentry(VALUE _message_builder, VALUE types, int argc,
-                           VALUE* argv) {
-#endif
-  MessageBuilderContext* message_builder =
-      ruby_to_MessageBuilderContext(_message_builder);
->>>>>>> master
-  VALUE type_class = rb_ary_entry(types, 2);
-  FileBuilderContext* file_context =
-      ruby_to_FileBuilderContext(message_builder->file_builder);
-  google_protobuf_MessageOptions* options =
-      google_protobuf_DescriptorProto_mutable_options(
-          message_builder->msg_proto, file_context->arena);
-
-  google_protobuf_MessageOptions_set_map_entry(options, true);
-
-  // optional <type> key = 1;
-  rb_funcall(_message_builder, rb_intern("optional"), 3,
-             ID2SYM(rb_intern("key")), rb_ary_entry(types, 0), INT2NUM(1));
-
-  // optional <type> value = 2;
-  if (type_class == Qnil) {
-    rb_funcall(_message_builder, rb_intern("optional"), 3,
-               ID2SYM(rb_intern("value")), rb_ary_entry(types, 1), INT2NUM(2));
-  } else {
-    rb_funcall(_message_builder, rb_intern("optional"), 4,
-               ID2SYM(rb_intern("value")), rb_ary_entry(types, 1), INT2NUM(2),
-               type_class);
-  }
-
-  return Qnil;
-}
-
-/*
- * call-seq:
- *     MessageBuilderContext.optional(name, type, number, type_class = nil,
- *                                    options = nil)
- *
- * Defines a new optional field on this message type with the given type, tag
- * number, and type class (for message and enum fields). The type must be a Ruby
- * symbol (as accepted by FieldDescriptor#type=) and the type_class must be a
- * string, if present (as accepted by FieldDescriptor#submsg_name=).
- */
-VALUE MessageBuilderContext_optional(int argc, VALUE* argv, VALUE _self) {
-  VALUE name, type, number;
-  VALUE type_class, options = Qnil;
-
-  rb_scan_args(argc, argv, "32", &name, &type, &number, &type_class, &options);
-
-  // Allow passing (name, type, number, options) or
-  // (name, type, number, type_class, options)
-  if (argc == 4 && RB_TYPE_P(type_class, T_HASH)) {
-    options = type_class;
-    type_class = Qnil;
-  }
-
-  msgdef_add_field(_self, UPB_LABEL_OPTIONAL, name, type, number, type_class,
-                   options, -1, false);
-
-  return Qnil;
-}
-
-/*
- * call-seq:
- *     MessageBuilderContext.proto3_optional(name, type, number,
- *                                           type_class = nil, options = nil)
- *
- * Defines a true proto3 optional field (that tracks presence) on this message
- * type with the given type, tag number, and type class (for message and enum
- * fields). The type must be a Ruby symbol (as accepted by
- * FieldDescriptor#type=) and the type_class must be a string, if present (as
- * accepted by FieldDescriptor#submsg_name=).
- */
-static VALUE MessageBuilderContext_proto3_optional(int argc, VALUE* argv,
-                                                   VALUE _self) {
-  VALUE name, type, number;
-  VALUE type_class, options = Qnil;
-
-  rb_scan_args(argc, argv, "32", &name, &type, &number, &type_class, &options);
-
-  // Allow passing (name, type, number, options) or
-  // (name, type, number, type_class, options)
-  if (argc == 4 && RB_TYPE_P(type_class, T_HASH)) {
-    options = type_class;
-    type_class = Qnil;
-  }
-
-  msgdef_add_field(_self, UPB_LABEL_OPTIONAL, name, type, number, type_class,
-                   options, -1, true);
-
-  return Qnil;
-}
-
-/*
- * call-seq:
- *     MessageBuilderContext.required(name, type, number, type_class = nil,
- *                                    options = nil)
- *
- * Defines a new required field on this message type with the given type, tag
- * number, and type class (for message and enum fields). The type must be a Ruby
- * symbol (as accepted by FieldDescriptor#type=) and the type_class must be a
- * string, if present (as accepted by FieldDescriptor#submsg_name=).
- *
- * Proto3 does not have required fields, but this method exists for
- * completeness. Any attempt to add a message type with required fields to a
- * pool will currently result in an error.
- */
-static VALUE MessageBuilderContext_required(int argc, VALUE* argv,
-                                            VALUE _self) {
-  VALUE name, type, number;
-  VALUE type_class, options = Qnil;
-
-  rb_scan_args(argc, argv, "32", &name, &type, &number, &type_class, &options);
-
-  // Allow passing (name, type, number, options) or
-  // (name, type, number, type_class, options)
-  if (argc == 4 && RB_TYPE_P(type_class, T_HASH)) {
-    options = type_class;
-    type_class = Qnil;
-  }
-
-  msgdef_add_field(_self, UPB_LABEL_REQUIRED, name, type, number, type_class,
-                   options, -1, false);
-
-  return Qnil;
-}
-
-/*
- * call-seq:
- *     MessageBuilderContext.repeated(name, type, number, type_class = nil)
- *
- * Defines a new repeated field on this message type with the given type, tag
- * number, and type class (for message and enum fields). The type must be a Ruby
- * symbol (as accepted by FieldDescriptor#type=) and the type_class must be a
- * string, if present (as accepted by FieldDescriptor#submsg_name=).
- */
-static VALUE MessageBuilderContext_repeated(int argc, VALUE* argv,
-                                            VALUE _self) {
-  VALUE name, type, number;
-  VALUE type_class, options = Qnil;
-
-  rb_scan_args(argc, argv, "32", &name, &type, &number, &type_class, &options);
-
-  // Allow passing (name, type, number, options) or
-  // (name, type, number, type_class, options)
-  if (argc == 4 && RB_TYPE_P(type_class, T_HASH)) {
-    options = type_class;
-    type_class = Qnil;
-  }
-
-  msgdef_add_field(_self, UPB_LABEL_REPEATED, name, type, number, type_class,
-                   options, -1, false);
-
-  return Qnil;
-}
-
-/*
- * call-seq:
- *     MessageBuilderContext.map(name, key_type, value_type, number,
- *                               value_type_class = nil)
- *
- * Defines a new map field on this message type with the given key and value
- * types, tag number, and type class (for message and enum value types). The key
- * type must be :int32/:uint32/:int64/:uint64, :bool, or :string. The value type
- * type must be a Ruby symbol (as accepted by FieldDescriptor#type=) and the
- * type_class must be a string, if present (as accepted by
- * FieldDescriptor#submsg_name=).
- */
-static VALUE MessageBuilderContext_map(int argc, VALUE* argv, VALUE _self) {
-  MessageBuilderContext* self = ruby_to_MessageBuilderContext(_self);
-  VALUE name, key_type, value_type, number, type_class;
-  VALUE mapentry_desc_name;
-  FileBuilderContext* file_builder;
-  upb_strview msg_name;
-
-  if (argc < 4) {
-    rb_raise(rb_eArgError, "Expected at least 4 arguments.");
-  }
-  name = argv[0];
-  key_type = argv[1];
-  value_type = argv[2];
-  number = argv[3];
-  type_class = (argc > 4) ? argv[4] : Qnil;
-
-  // Validate the key type. We can't accept enums, messages, or floats/doubles
-  // as map keys. (We exclude these explicitly, and the field-descriptor setter
-  // below then ensures that the type is one of the remaining valid options.)
-  if (SYM2ID(key_type) == rb_intern("float") ||
-      SYM2ID(key_type) == rb_intern("double") ||
-      SYM2ID(key_type) == rb_intern("enum") ||
-      SYM2ID(key_type) == rb_intern("message")) {
-    rb_raise(rb_eArgError,
-             "Cannot add a map field with a float, double, enum, or message "
-             "type.");
-  }
-
-  file_builder = ruby_to_FileBuilderContext(self->file_builder);
-
-  // Create a new message descriptor for the map entry message, and create a
-  // repeated submessage field here with that type.
-  msg_name = google_protobuf_DescriptorProto_name(self->msg_proto);
-  mapentry_desc_name = rb_str_new(msg_name.data, msg_name.size);
-  mapentry_desc_name = rb_str_cat2(mapentry_desc_name, "_MapEntry_");
-  mapentry_desc_name =
-      rb_str_cat2(mapentry_desc_name, rb_id2name(SYM2ID(name)));
-
-  {
-    // message <msgname>_MapEntry_ { /* ... */ }
-    VALUE args[1] = {mapentry_desc_name};
-    VALUE types = rb_ary_new3(3, key_type, value_type, type_class);
-    rb_block_call(self->file_builder, rb_intern("add_message"), 1, args,
-                  make_mapentry, types);
-  }
-
-  // If this file is in a package, we need to qualify the map entry type.
-  if (google_protobuf_FileDescriptorProto_has_package(file_builder->file_proto)) {
-    upb_strview package_view =
-        google_protobuf_FileDescriptorProto_package(file_builder->file_proto);
-    VALUE package = rb_str_new(package_view.data, package_view.size);
-    package = rb_str_cat2(package, ".");
-    mapentry_desc_name = rb_str_concat(package, mapentry_desc_name);
-  }
-
-  // repeated MapEntry <name> = <number>;
-  rb_funcall(_self, rb_intern("repeated"), 4, name,
-             ID2SYM(rb_intern("message")), number, mapentry_desc_name);
-
-  return Qnil;
-}
-
-/*
- * call-seq:
- *     MessageBuilderContext.oneof(name, &block) => nil
- *
- * Creates a new OneofDescriptor with the given name, creates a
- * OneofBuilderContext attached to that OneofDescriptor, evaluates the given
- * block in the context of that OneofBuilderContext with #instance_eval, and
- * then adds the oneof to the message.
- *
- * This is the recommended, idiomatic way to build oneof definitions.
- */
-static VALUE MessageBuilderContext_oneof(VALUE _self, VALUE name) {
-  MessageBuilderContext* self = ruby_to_MessageBuilderContext(_self);
-  size_t oneof_count;
-  FileBuilderContext* file_context =
-      ruby_to_FileBuilderContext(self->file_builder);
-  google_protobuf_OneofDescriptorProto* oneof_proto;
-
-  // Existing oneof_count becomes oneof_index.
-  google_protobuf_DescriptorProto_oneof_decl(self->msg_proto, &oneof_count);
-
-  // Create oneof_proto and set its name.
-  oneof_proto = google_protobuf_DescriptorProto_add_oneof_decl(
-      self->msg_proto, file_context->arena);
-  google_protobuf_OneofDescriptorProto_set_name(
-      oneof_proto, FileBuilderContext_strdup_sym(self->file_builder, name));
-
-  // Evaluate the block with the builder as argument.
-  {
-    VALUE args[2] = { INT2NUM(oneof_count), _self };
-    VALUE ctx = rb_class_new_instance(2, args, cOneofBuilderContext);
-    VALUE block = rb_block_proc();
-    rb_funcall_with_block(ctx, rb_intern("instance_eval"), 0, NULL, block);
-  }
-
-  return Qnil;
-}
-
-static void MessageBuilderContext_add_synthetic_oneofs(VALUE _self) {
-  MessageBuilderContext* self = ruby_to_MessageBuilderContext(_self);
-  FileBuilderContext* file_context =
-      ruby_to_FileBuilderContext(self->file_builder);
-  size_t field_count, oneof_count;
-  google_protobuf_FieldDescriptorProto** fields =
-      google_protobuf_DescriptorProto_mutable_field(self->msg_proto, &field_count);
-  const google_protobuf_OneofDescriptorProto*const* oneofs =
-      google_protobuf_DescriptorProto_oneof_decl(self->msg_proto, &oneof_count);
-  VALUE names = rb_hash_new();
-  VALUE underscore = rb_str_new2("_");
-  size_t i;
-
-  // We have to build a set of all names, to ensure that synthetic oneofs are
-  // not creating conflicts.
-  for (i = 0; i < field_count; i++) {
-    upb_strview name = google_protobuf_FieldDescriptorProto_name(fields[i]);
-    rb_hash_aset(names, rb_str_new(name.data, name.size), Qtrue);
-  }
-  for (i = 0; i < oneof_count; i++) {
-    upb_strview name = google_protobuf_OneofDescriptorProto_name(oneofs[i]);
-    rb_hash_aset(names, rb_str_new(name.data, name.size), Qtrue);
-  }
-
-  for (i = 0; i < field_count; i++) {
-    google_protobuf_OneofDescriptorProto* oneof_proto;
-    VALUE oneof_name;
-    upb_strview field_name;
-
-    if (!google_protobuf_FieldDescriptorProto_proto3_optional(fields[i])) {
-      continue;
-    }
-
-    // Prepend '_' until we are no longer conflicting.
-    field_name = google_protobuf_FieldDescriptorProto_name(fields[i]);
-    oneof_name = rb_str_new(field_name.data, field_name.size);
-    while (rb_hash_lookup(names, oneof_name) != Qnil) {
-      oneof_name = rb_str_plus(underscore, oneof_name);
-    }
-
-    rb_hash_aset(names, oneof_name, Qtrue);
-    google_protobuf_FieldDescriptorProto_set_oneof_index(fields[i],
-                                                         oneof_count++);
-    oneof_proto = google_protobuf_DescriptorProto_add_oneof_decl(
-        self->msg_proto, file_context->arena);
-    google_protobuf_OneofDescriptorProto_set_name(
-        oneof_proto, FileBuilderContext_strdup(self->file_builder, oneof_name));
-  }
-}
-
-static void MessageBuilderContext_register(VALUE module) {
-  VALUE klass = rb_define_class_under(
-      module, "MessageBuilderContext", rb_cObject);
-  rb_define_alloc_func(klass, MessageBuilderContext_alloc);
-  rb_define_method(klass, "initialize",
-                   MessageBuilderContext_initialize, 2);
-  rb_define_method(klass, "optional", MessageBuilderContext_optional, -1);
-  rb_define_method(klass, "proto3_optional", MessageBuilderContext_proto3_optional, -1);
-  rb_define_method(klass, "required", MessageBuilderContext_required, -1);
-  rb_define_method(klass, "repeated", MessageBuilderContext_repeated, -1);
-  rb_define_method(klass, "map", MessageBuilderContext_map, -1);
-  rb_define_method(klass, "oneof", MessageBuilderContext_oneof, 1);
-  rb_gc_register_address(&cMessageBuilderContext);
-  cMessageBuilderContext = klass;
-}
-
-// -----------------------------------------------------------------------------
-// OneofBuilderContext.
-// -----------------------------------------------------------------------------
-
-typedef struct {
-  int oneof_index;
-  VALUE message_builder;
-} OneofBuilderContext;
-
-static VALUE cOneofBuilderContext = Qnil;
-
-void OneofBuilderContext_mark(void* _self) {
-  OneofBuilderContext* self = _self;
-  rb_gc_mark(self->message_builder);
-}
-
-static const rb_data_type_t OneofBuilderContext_type = {
-  "Google::Protobuf::Internal::OneofBuilderContext",
-  {OneofBuilderContext_mark, RUBY_DEFAULT_FREE, NULL},
-  .flags = RUBY_TYPED_FREE_IMMEDIATELY,
-};
-
-static OneofBuilderContext* ruby_to_OneofBuilderContext(VALUE val) {
-  OneofBuilderContext* ret;
-  TypedData_Get_Struct(val, OneofBuilderContext, &OneofBuilderContext_type,
-                       ret);
-  return ret;
-}
-
-static VALUE OneofBuilderContext_alloc(VALUE klass) {
-  OneofBuilderContext* self = ALLOC(OneofBuilderContext);
-  VALUE ret = TypedData_Wrap_Struct(klass, &OneofBuilderContext_type, self);
-  self->oneof_index = 0;
-  self->message_builder = Qnil;
-  return ret;
-}
-
-/*
- * call-seq:
- *     OneofBuilderContext.new(oneof_index, message_builder) => context
- *
- * Create a new oneof builder context around the given oneof descriptor and
- * builder context. This class is intended to serve as a DSL context to be used
- * with #instance_eval.
- */
-static VALUE OneofBuilderContext_initialize(VALUE _self, VALUE oneof_index,
-                                            VALUE message_builder) {
-  OneofBuilderContext* self = ruby_to_OneofBuilderContext(_self);
-  self->oneof_index = NUM2INT(oneof_index);
-  self->message_builder = message_builder;
-  return Qnil;
-}
-
-/*
- * call-seq:
- *     OneofBuilderContext.optional(name, type, number, type_class = nil,
- *                                  default_value = nil)
- *
- * Defines a new optional field in this oneof with the given type, tag number,
- * and type class (for message and enum fields). The type must be a Ruby symbol
- * (as accepted by FieldDescriptor#type=) and the type_class must be a string,
- * if present (as accepted by FieldDescriptor#submsg_name=).
- */
-static VALUE OneofBuilderContext_optional(int argc, VALUE* argv, VALUE _self) {
-  OneofBuilderContext* self = ruby_to_OneofBuilderContext(_self);
-  VALUE name, type, number;
-  VALUE type_class, options = Qnil;
-
-  rb_scan_args(argc, argv, "32", &name, &type, &number, &type_class, &options);
-
-  msgdef_add_field(self->message_builder, UPB_LABEL_OPTIONAL, name, type,
-                   number, type_class, options, self->oneof_index, false);
-
-  return Qnil;
-}
-
-static void OneofBuilderContext_register(VALUE module) {
-  VALUE klass = rb_define_class_under(
-      module, "OneofBuilderContext", rb_cObject);
-  rb_define_alloc_func(klass, OneofBuilderContext_alloc);
-  rb_define_method(klass, "initialize",
-                   OneofBuilderContext_initialize, 2);
-  rb_define_method(klass, "optional", OneofBuilderContext_optional, -1);
-  rb_gc_register_address(&cOneofBuilderContext);
-  cOneofBuilderContext = klass;
-}
-
-// -----------------------------------------------------------------------------
-// EnumBuilderContext.
-// -----------------------------------------------------------------------------
-
-typedef struct {
-  google_protobuf_EnumDescriptorProto* enum_proto;
-  VALUE file_builder;
-} EnumBuilderContext;
-
-static VALUE cEnumBuilderContext = Qnil;
-
-void EnumBuilderContext_mark(void* _self) {
-  EnumBuilderContext* self = _self;
-  rb_gc_mark(self->file_builder);
-}
-
-static const rb_data_type_t EnumBuilderContext_type = {
-  "Google::Protobuf::Internal::EnumBuilderContext",
-  {EnumBuilderContext_mark, RUBY_DEFAULT_FREE, NULL},
-  .flags = RUBY_TYPED_FREE_IMMEDIATELY,
-};
-
-static EnumBuilderContext* ruby_to_EnumBuilderContext(VALUE val) {
-  EnumBuilderContext* ret;
-  TypedData_Get_Struct(val, EnumBuilderContext, &EnumBuilderContext_type, ret);
-  return ret;
-}
-
-static VALUE EnumBuilderContext_alloc(VALUE klass) {
-  EnumBuilderContext* self = ALLOC(EnumBuilderContext);
-  VALUE ret = TypedData_Wrap_Struct(klass, &EnumBuilderContext_type, self);
-  self->enum_proto = NULL;
-  self->file_builder = Qnil;
-  return ret;
-}
-
-/*
- * call-seq:
- *     EnumBuilderContext.new(file_builder) => context
- *
- * Create a new builder context around the given enum descriptor. This class is
- * intended to serve as a DSL context to be used with #instance_eval.
- */
-static VALUE EnumBuilderContext_initialize(VALUE _self, VALUE _file_builder,
-                                           VALUE name) {
-  EnumBuilderContext* self = ruby_to_EnumBuilderContext(_self);
-  FileBuilderContext* file_builder = ruby_to_FileBuilderContext(_file_builder);
-  google_protobuf_FileDescriptorProto* file_proto = file_builder->file_proto;
-
-  self->file_builder = _file_builder;
-  self->enum_proto = google_protobuf_FileDescriptorProto_add_enum_type(
-      file_proto, file_builder->arena);
-
-  google_protobuf_EnumDescriptorProto_set_name(
-      self->enum_proto, FileBuilderContext_strdup(_file_builder, name));
-
-  return Qnil;
-}
-
-/*
- * call-seq:
- *     EnumBuilder.add_value(name, number)
- *
- * Adds the given name => number mapping to the enum type. Name must be a Ruby
- * symbol.
- */
-static VALUE EnumBuilderContext_value(VALUE _self, VALUE name, VALUE number) {
-  EnumBuilderContext* self = ruby_to_EnumBuilderContext(_self);
-  FileBuilderContext* file_builder =
-      ruby_to_FileBuilderContext(self->file_builder);
-  google_protobuf_EnumValueDescriptorProto* enum_value;
-
-  enum_value = google_protobuf_EnumDescriptorProto_add_value(
-      self->enum_proto, file_builder->arena);
-
-  google_protobuf_EnumValueDescriptorProto_set_name(
-      enum_value, FileBuilderContext_strdup_sym(self->file_builder, name));
-  google_protobuf_EnumValueDescriptorProto_set_number(enum_value,
-                                                      NUM2INT(number));
-
-  return Qnil;
-}
-
-static void EnumBuilderContext_register(VALUE module) {
-  VALUE klass = rb_define_class_under(
-      module, "EnumBuilderContext", rb_cObject);
-  rb_define_alloc_func(klass, EnumBuilderContext_alloc);
-  rb_define_method(klass, "initialize", EnumBuilderContext_initialize, 2);
-  rb_define_method(klass, "value", EnumBuilderContext_value, 2);
-  rb_gc_register_address(&cEnumBuilderContext);
-  cEnumBuilderContext = klass;
-}
-
-// -----------------------------------------------------------------------------
-// Builder.
-// -----------------------------------------------------------------------------
-
-typedef struct {
-  VALUE descriptor_pool;
-  VALUE default_file_builder;
-} Builder;
-
-static VALUE cBuilder = Qnil;
-
-static void Builder_mark(void* _self) {
-  Builder* self = _self;
-  rb_gc_mark(self->descriptor_pool);
-  rb_gc_mark(self->default_file_builder);
-}
-
-static const rb_data_type_t Builder_type = {
-  "Google::Protobuf::Internal::Builder",
-  {Builder_mark, RUBY_DEFAULT_FREE, NULL},
-  .flags = RUBY_TYPED_FREE_IMMEDIATELY,
-};
-
-static Builder* ruby_to_Builder(VALUE val) {
-  Builder* ret;
-  TypedData_Get_Struct(val, Builder, &Builder_type, ret);
-  return ret;
-}
-
-static VALUE Builder_alloc(VALUE klass) {
-  Builder* self = ALLOC(Builder);
-  VALUE ret = TypedData_Wrap_Struct(klass, &Builder_type, self);
-  self->descriptor_pool = Qnil;
-  self->default_file_builder = Qnil;
-  return ret;
-}
-
-/*
- * call-seq:
- *     Builder.new(descriptor_pool) => builder
- *
- * Creates a new Builder. A Builder can accumulate a set of new message and enum
- * descriptors and atomically register them into a pool in a way that allows for
- * (co)recursive type references.
- */
-static VALUE Builder_initialize(VALUE _self, VALUE pool) {
-  Builder* self = ruby_to_Builder(_self);
-  self->descriptor_pool = pool;
-  self->default_file_builder = Qnil;  // Created lazily if needed.
-  return Qnil;
-}
-
-/*
- * call-seq:
- *     Builder.add_file(name, options = nil, &block)
- *
- * Creates a new, file descriptor with the given name and options and invokes
- * the block in the context of a FileBuilderContext on that descriptor. The
- * block can then call FileBuilderContext#add_message or
- * FileBuilderContext#add_enum to define new messages or enums, respectively.
- *
- * This is the recommended, idiomatic way to build file descriptors.
- */
-static VALUE Builder_add_file(int argc, VALUE* argv, VALUE _self) {
-  Builder* self = ruby_to_Builder(_self);
-  VALUE name, options;
-  VALUE ctx;
-  VALUE block;
-
-  rb_scan_args(argc, argv, "11", &name, &options);
-
-  {
-    VALUE args[3] = { self->descriptor_pool, name, options };
-    ctx = rb_class_new_instance(3, args, cFileBuilderContext);
-  }
-
-  block = rb_block_proc();
-  rb_funcall_with_block(ctx, rb_intern("instance_eval"), 0, NULL, block);
-  FileBuilderContext_build(ctx);
-
-  return Qnil;
-}
-
-static VALUE Builder_get_default_file(VALUE _self) {
-  Builder* self = ruby_to_Builder(_self);
-
-  /* Lazily create only if legacy builder-level methods are called. */
-  if (self->default_file_builder == Qnil) {
-    VALUE name = rb_str_new2("ruby_default_file.proto");
-    VALUE args [3] = { self->descriptor_pool, name, rb_hash_new() };
-    self->default_file_builder =
-        rb_class_new_instance(3, args, cFileBuilderContext);
-  }
-
-  return self->default_file_builder;
-}
-
-/*
- * call-seq:
- *     Builder.add_message(name, &block)
- *
- * Old and deprecated way to create a new descriptor.
- * See FileBuilderContext.add_message for the recommended way.
- *
- * Exists for backwards compatibility to allow building descriptor pool for
- * files generated by protoc which don't add messages within "add_file" block.
- * Descriptors created this way get assigned to a default empty FileDescriptor.
- */
-static VALUE Builder_add_message(VALUE _self, VALUE name) {
-  VALUE file_builder = Builder_get_default_file(_self);
-  rb_funcall_with_block(file_builder, rb_intern("add_message"), 1, &name,
-                        rb_block_proc());
-  return Qnil;
-}
-
-/*
- * call-seq:
- *     Builder.add_enum(name, &block)
- *
- * Old and deprecated way to create a new enum descriptor.
- * See FileBuilderContext.add_enum for the recommended way.
- *
- * Exists for backwards compatibility to allow building descriptor pool for
- * files generated by protoc which don't add enums within "add_file" block.
- * Enum descriptors created this way get assigned to a default empty
- * FileDescriptor.
- */
-static VALUE Builder_add_enum(VALUE _self, VALUE name) {
-  VALUE file_builder = Builder_get_default_file(_self);
-  rb_funcall_with_block(file_builder, rb_intern("add_enum"), 1, &name,
-                        rb_block_proc());
-  return Qnil;
-}
-
-/* This method is hidden from Ruby, and only called directly from
- * DescriptorPool_build(). */
-static VALUE Builder_build(VALUE _self) {
-  Builder* self = ruby_to_Builder(_self);
-
-  if (self->default_file_builder != Qnil) {
-    FileBuilderContext_build(self->default_file_builder);
-    self->default_file_builder = Qnil;
-  }
-
-  return Qnil;
-}
-
-static void Builder_register(VALUE module) {
-  VALUE klass = rb_define_class_under(module, "Builder", rb_cObject);
-  rb_define_alloc_func(klass, Builder_alloc); 
-  rb_define_method(klass, "initialize", Builder_initialize, 1);
-  rb_define_method(klass, "add_file", Builder_add_file, -1);
-  rb_define_method(klass, "add_message", Builder_add_message, 1);
-  rb_define_method(klass, "add_enum", Builder_add_enum, 1);
-  rb_gc_register_address(&cBuilder);
-  cBuilder = klass;
-}
-
 static VALUE get_def_obj(VALUE _descriptor_pool, const void* ptr, VALUE klass) {
   DescriptorPool* descriptor_pool = ruby_to_DescriptorPool(_descriptor_pool);
   VALUE key = ULL2NUM((intptr_t)ptr);
@@ -2602,11 +1278,6 @@
   FieldDescriptor_register(module);
   OneofDescriptor_register(module);
   EnumDescriptor_register(module);
-  FileBuilderContext_register(module);
-  MessageBuilderContext_register(module);
-  OneofBuilderContext_register(module);
-  EnumBuilderContext_register(module);
-  Builder_register(module);
 
   rb_gc_register_address(&c_only_cookie);
   c_only_cookie = rb_class_new_instance(0, NULL, rb_cObject);
diff --git a/ruby/lib/google/protobuf.rb b/ruby/lib/google/protobuf.rb
index 83ece4c..9368768 100644
--- a/ruby/lib/google/protobuf.rb
+++ b/ruby/lib/google/protobuf.rb
@@ -51,75 +51,7 @@
     require 'google/protobuf_c'
   end
 
-  module Google
-    module Protobuf
-      module Internal
-        def self.infer_package(names)
-          # Package is longest common prefix ending in '.', if any.
-          if not names.empty?
-            min, max = names.minmax
-            last_common_dot = nil
-            min.size.times { |i|
-              if min[i] != max[i] then break end
-              if min[i] == ?. then last_common_dot = i end
-            }
-            if last_common_dot
-              return min.slice(0, last_common_dot)
-            end
-          end
-
-          nil
-        end
-
-        class NestingBuilder
-          def initialize(msg_names, enum_names)
-            @to_pos = {nil=>nil}
-            @msg_children = Hash.new { |hash, key| hash[key] = [] }
-            @enum_children = Hash.new { |hash, key| hash[key] = [] }
-
-            msg_names.each_with_index { |name, idx| @to_pos[name] = idx }
-            enum_names.each_with_index { |name, idx| @to_pos[name] = idx }
-
-            msg_names.each { |name| @msg_children[parent(name)] << name }
-            enum_names.each { |name| @enum_children[parent(name)] << name }
-          end
-
-          def build(package)
-            return build_msg(package)
-          end
-
-          private
-          def build_msg(msg)
-            return {
-              :pos => @to_pos[msg],
-              :msgs => @msg_children[msg].map { |child| build_msg(child) },
-              :enums => @enum_children[msg].map { |child| @to_pos[child] },
-            }
-          end
-
-          private
-          def parent(name)
-            idx = name.rindex(?.)
-            if idx
-              return name.slice(0, idx)
-            else
-              return nil
-            end
-          end
-        end
-
-        def self.fixup_descriptor(package, msg_names, enum_names)
-          if package.nil?
-            package = self.infer_package(msg_names + enum_names)
-          end
-
-          nesting = NestingBuilder.new(msg_names, enum_names).build(package)
-
-          return package, nesting
-        end
-      end
-    end
-  end
+  require 'google/protobuf/descriptor_dsl'
 end
 
 require 'google/protobuf/repeated_field'
diff --git a/ruby/lib/google/protobuf/descriptor_builder.rb b/ruby/lib/google/protobuf/descriptor_builder.rb
deleted file mode 100644
index af485bd..0000000
--- a/ruby/lib/google/protobuf/descriptor_builder.rb
+++ /dev/null
@@ -1,110 +0,0 @@
-#!/usr/bin/ruby
-#
-# Summary description of library or script.
-#
-# This doc string should contain an overall description of the module/script
-# and can optionally briefly describe exported classes and functions.
-#
-#    ClassFoo:      One line summary.
-#    function_foo:  One line summary.
-#
-# $Id$
-
-module Google
-  module Protobuf
-    module Internal
-
-      class FileBuilder
-        def initialize(pool, name, options=nil)
-          @pool = pool
-          @file_proto = Google::Protobuf::FileDescriptorProto.new
-          @file_proto.name = name
-          @file_proto.syntax = "proto3"  # Default syntax for Ruby is proto3.
-
-          if options
-            if options.key?(:syntax)
-              @file_proto.syntax = options[:key].to_s
-            end
-          end
-        end
-
-        def add_message(name, &block)
-          MessageBuilder.new(name, @file_proto).instance_eval &block
-        end
-
-        def add_enum(name, &block)
-          enum_proto = Google::Protobuf::
-          EnumBuilder.new(name, @file_proto).instance_eval &block
-        end
-      end
-
-      class MessageBuilder
-        def initialize(name, file_proto)
-          @msg_proto = Google::Protobuf::DescriptorProto.new
-          @msg_proto.name = name
-          file_proto.message_type << @msg_proto
-        end
-
-        def optional(name, type, number, type_class=nil, options=nil)
-          # Allow passing either:
-          # - (name, type, number, options) or
-          # - (name, type, number, type_class, options)
-          if options.nil? and type_class.instance_of?(Hash)
-            options = type_class;
-            type_class = Qnil;
-          end
-          add_field(:LABEL_OPTIONAL, name, type, number, type_class, options)
-        end
-
-        def required(name, type, number, type_class=nil, options=nil)
-          # Allow passing either:
-          # - (name, type, number, options) or
-          # - (name, type, number, type_class, options)
-          if options.nil? and type_class.instance_of?(Hash)
-            options = type_class;
-            type_class = Qnil;
-          end
-          add_field(:LABEL_REQUIRED, name, type, number, type_class, options)
-        end
-
-        def repeated(name, type, number, type_class = nil)
-          add_field(:LABEL_REPEATED, name, type, number, type_class, nil)
-        end
-
-        def map(name, key_type, value_type, number, value_type_class = nil)
-          entry_name = "MapEntry_#{name}"
-          add_message
-        end
-
-        private def add_field(label, name, type, number, type_class, options,
-                              oneof_index)
-          field_proto = Google::Protobuf::FieldDescriptorProto.new(
-            :label => label,
-            :name => name,
-            :type => type,
-            :number => number
-          )
-
-          if type_class
-            # Make it an absolute type name by prepending a dot.
-            field_proto.type_name = "." + type_class
-          end
-
-          if oneof_index
-            field_proto.oneof_index = oneof_index
-          end
-
-          if options
-            if options.key?(:default)
-              # Call #to_s since all defaults are strings in the descriptor.
-              field_proto.default_value = options[:default].to_s
-            end
-          end
-
-          @msg_proto.field << field_proto
-        end
-      end
-
-    end
-  end
-end
diff --git a/ruby/lib/google/protobuf/descriptor_dsl.rb b/ruby/lib/google/protobuf/descriptor_dsl.rb
new file mode 100644
index 0000000..f38db6f
--- /dev/null
+++ b/ruby/lib/google/protobuf/descriptor_dsl.rb
@@ -0,0 +1,440 @@
+#!/usr/bin/ruby
+#
+# Code that implements the DSL for defining proto messages.
+
+require 'google/protobuf/descriptor_pb'
+
+module Google
+  module Protobuf
+    module Internal
+      class Builder
+        def initialize(pool)
+          @pool = pool
+          @default_file = nil  # Constructed lazily
+        end
+
+        def add_file(name, options={}, &block)
+          builder = FileBuilder.new(@pool, name, options)
+          builder.instance_eval(&block)
+          internal_add_file(builder)
+        end
+
+        def add_message(name, &block)
+          internal_default_file.add_message(name, &block)
+        end
+
+        def add_enum(name, &block)
+          internal_default_file.add_enum(name, &block)
+        end
+
+        # ---- Internal methods, not part of the DSL ----
+
+        def build
+          if @default_file
+            internal_add_file(@default_file)
+          end
+        end
+
+        private def internal_add_file(file_builder)
+          proto = file_builder.build
+          serialized = Google::Protobuf::FileDescriptorProto.encode(proto)
+          @pool.add_serialized_file(serialized)
+        end
+
+        private def internal_default_file
+          @default_file ||= FileBuilder.new(@pool, "ruby_default_file.proto")
+        end
+      end
+
+      class FileBuilder
+        def initialize(pool, name, options={})
+          @pool = pool
+          @file_proto = Google::Protobuf::FileDescriptorProto.new(
+            name: name,
+            syntax: options.fetch(:syntax, "proto3")
+          )
+        end
+
+        def add_message(name, &block)
+          builder = MessageBuilder.new(name, self, @file_proto)
+          builder.instance_eval(&block)
+          builder.internal_add_synthetic_oneofs
+        end
+
+        def add_enum(name, &block)
+          EnumBuilder.new(name, @file_proto).instance_eval(&block)
+        end
+
+        # ---- Internal methods, not part of the DSL ----
+
+        # These methods fix up the file descriptor to account for differences
+        # between the DSL and FileDescriptorProto.
+
+        # The DSL can omit a package name; here we infer what the package is if
+        # was not specified.
+        def infer_package(names)
+          # Package is longest common prefix ending in '.', if any.
+          if not names.empty?
+            min, max = names.minmax
+            last_common_dot = nil
+            min.size.times { |i|
+              if min[i] != max[i] then break end
+              if min[i] == ?. then last_common_dot = i end
+            }
+            if last_common_dot
+              return min.slice(0, last_common_dot)
+            end
+          end
+
+          nil
+        end
+
+        def rewrite_enum_default(field)
+          if field.type != :TYPE_ENUM or !field.has_default_value? or !field.has_type_name?
+            return
+          end
+
+          value = field.default_value
+          type_name = field.type_name
+
+          if value.empty? or value[0].ord < ?0.ord or value[0].ord > ?9.ord
+            return
+          end
+
+          if type_name.empty? || type_name[0] != ?.
+            return
+          end
+
+          type_name = type_name[1..-1]
+          as_int = Integer(value) rescue return
+
+          enum_desc = @pool.lookup(type_name)
+          if enum_desc.is_a?(Google::Protobuf::EnumDescriptor)
+            # Enum was defined in a previous file.
+            name = enum_desc.lookup_value(as_int)
+            if name
+              # Update the default value in the proto.
+              field.default_value = name
+            end
+          else
+            # See if enum was defined in this file.
+            @file_proto.enum_type.each { |enum_proto|
+              if enum_proto.name == type_name
+                enum_proto.value.each { |enum_value_proto|
+                  if enum_value_proto.number == as_int
+                    # Update the default value in the proto.
+                    field.default_value = enum_value_proto.name
+                    return
+                  end
+                }
+                # We found the right enum, but no value matched.
+                return
+              end
+            }
+          end
+        end
+
+        # Historically we allowed enum defaults to be specified as a number.
+        # In retrospect this was a mistake as descriptors require defaults to
+        # be specified as a label. This can make a difference if multiple
+        # labels have the same number.
+        #
+        # Here we do a pass over all enum defaults and rewrite numeric defaults
+        # by looking up their labels.  This is complicated by the fact that the
+        # enum definition can live in either the symtab or the file_proto.
+        #
+        # We take advantage of the fact that this is called *before* enums or
+        # messages are nested in other messages, so we only have to iterate
+        # one level deep.
+        def rewrite_enum_defaults
+          @file_proto.message_type.each { |msg|
+            msg.field.each { |field|
+              rewrite_enum_default(field)
+            }
+          }
+        end
+
+        # We have to do some relatively complicated logic here for backward
+        # compatibility.
+        #
+        # In descriptor.proto, messages are nested inside other messages if that is
+        # what the original .proto file looks like.  For example, suppose we have this
+        # foo.proto:
+        #
+        # package foo;
+        # message Bar {
+        #   message Baz {}
+        # }
+        #
+        # The descriptor for this must look like this:
+        #
+        # file {
+        #   name: "test.proto"
+        #   package: "foo"
+        #   message_type {
+        #     name: "Bar"
+        #     nested_type {
+        #       name: "Baz"
+        #     }
+        #   }
+        # }
+        #
+        # However, the Ruby generated code has always generated messages in a flat,
+        # non-nested way:
+        #
+        # Google::Protobuf::DescriptorPool.generated_pool.build do
+        #   add_message "foo.Bar" do
+        #   end
+        #   add_message "foo.Bar.Baz" do
+        #   end
+        # end
+        #
+        # Here we need to do a translation where we turn this generated code into the
+        # above descriptor.  We need to infer that "foo" is the package name, and not
+        # a message itself. */
+
+        def get_parent_name(msg_or_enum)
+          name = msg_or_enum.name
+          idx = name.rindex(?.)
+          if idx
+            msg_or_enum.name = name[idx+1..-1]
+            return name[0...idx]
+          else
+            return nil
+          end
+        end
+
+        def get_parent_msg(msgs_by_name, name, parent_name)
+          parent_msg = msgs_by_name[parent_name]
+          if parent_msg.nil?
+            raise "To define name #{name}, there must be a message named #{parent_name} to enclose it"
+          end
+          return parent_msg
+        end
+
+        def fix_nesting
+          # Calculate and update package.
+          msgs_by_name = @file_proto.message_type.map { |msg| [msg.name, msg] }.to_h
+          enum_names = @file_proto.enum_type.map { |enum_proto| enum_proto.name }
+
+          package = infer_package(msgs_by_name.keys + enum_names)
+          if package
+            @file_proto.package = package
+          end
+
+          # Update nesting based on package.
+          final_msgs = Google::Protobuf::RepeatedField.new(:message, Google::Protobuf::DescriptorProto)
+          final_enums = Google::Protobuf::RepeatedField.new(:message, Google::Protobuf::EnumDescriptorProto)
+
+          # Note: We don't iterate over msgs_by_name.values because we want to
+          # preserve order as listed in the DSL.
+          @file_proto.message_type.each { |msg|
+            parent_name = get_parent_name(msg)
+            if parent_name == package
+              final_msgs << msg
+            else
+              get_parent_msg(msgs_by_name, msg.name, parent_name).nested_type << msg
+            end
+          }
+
+          @file_proto.enum_type.each { |enum|
+            parent_name = get_parent_name(enum)
+            if parent_name == package
+              final_enums << enum
+            else
+              get_parent_msg(msgs_by_name, enum.name, parent_name).enum_type << enum
+            end
+          }
+
+          @file_proto.message_type = final_msgs
+          @file_proto.enum_type = final_enums
+        end
+
+        def internal_file_proto
+          @file_proto
+        end
+
+        def build
+          rewrite_enum_defaults
+          fix_nesting
+          return @file_proto
+        end
+      end
+
+      class MessageBuilder
+        def initialize(name, file_builder, file_proto)
+          @file_builder = file_builder
+          @msg_proto = Google::Protobuf::DescriptorProto.new(
+            :name => name
+          )
+          file_proto.message_type << @msg_proto
+        end
+
+        def optional(name, type, number, type_class=nil, options=nil)
+          internal_add_field(:LABEL_OPTIONAL, name, type, number, type_class, options)
+        end
+
+        def proto3_optional(name, type, number, type_class=nil, options=nil)
+          internal_add_field(:LABEL_OPTIONAL, name, type, number, type_class, options,
+                             proto3_optional: true)
+        end
+
+        def required(name, type, number, type_class=nil, options=nil)
+          internal_add_field(:LABEL_REQUIRED, name, type, number, type_class, options)
+        end
+
+        def repeated(name, type, number, type_class = nil)
+          internal_add_field(:LABEL_REPEATED, name, type, number, type_class, nil)
+        end
+
+        def oneof(name, &block)
+          OneofBuilder.new(name, self).instance_eval(&block)
+        end
+
+        # Defines a new map field on this message type with the given key and
+        # value types, tag number, and type class (for message and enum value
+        # types). The key type must be :int32/:uint32/:int64/:uint64, :bool, or
+        # :string. The value type type must be a Ruby symbol (as accepted by
+        # FieldDescriptor#type=) and the type_class must be a string, if
+        # present (as accepted by FieldDescriptor#submsg_name=).
+        def map(name, key_type, value_type, number, value_type_class = nil)
+          if key_type == :float or key_type == :double or key_type == :enum or
+             key_type == :message
+            raise ArgError, "Not an acceptable key type: " + key_type
+          end
+          entry_name = "#{@msg_proto.name}_MapEntry_#{name}"
+
+          @file_builder.add_message entry_name do
+            optional :key, key_type, 1
+            optional :value, value_type, 2, value_type_class
+          end
+          options = @file_builder.internal_file_proto.message_type.last.options ||= MessageOptions.new
+          options.map_entry = true
+          repeated name, :message, number, entry_name
+        end
+
+        # ---- Internal methods, not part of the DSL ----
+
+        def internal_add_synthetic_oneofs
+          # We have to build a set of all names, to ensure that synthetic oneofs
+          # are not creating conflicts
+          names = {}
+          @msg_proto.field.each { |field| names[field.name] = true }
+          @msg_proto.oneof_decl.each { |oneof| names[oneof.name] = true }
+
+          @msg_proto.field.each { |field|
+            if field.proto3_optional
+              # Prepend '_' until we are no longer conflicting.
+              oneof_name = field.name
+              while names[oneof_name]
+                oneof_name = "_" + oneof_name
+              end
+              names[oneof_name] = true
+              field.oneof_index = @msg_proto.oneof_decl.size
+              @msg_proto.oneof_decl << Google::Protobuf::OneofDescriptorProto.new(
+                name: oneof_name
+              )
+            end
+          }
+        end
+
+        def internal_add_field(label, name, type, number, type_class, options,
+                               oneof_index: nil, proto3_optional: false)
+          # Allow passing either:
+          # - (name, type, number, options) or
+          # - (name, type, number, type_class, options)
+          if options.nil? and type_class.instance_of?(Hash)
+            options = type_class;
+            type_class = nil;
+          end
+
+          field_proto = Google::Protobuf::FieldDescriptorProto.new(
+            :label => label,
+            :name => name,
+            :type => ("TYPE_" + type.to_s.upcase).to_sym,
+            :number => number
+          )
+
+          if type_class
+            # Make it an absolute type name by prepending a dot.
+            field_proto.type_name = "." + type_class
+          end
+
+          if oneof_index
+            field_proto.oneof_index = oneof_index
+          end
+
+          if proto3_optional
+            field_proto.proto3_optional = true
+          end
+
+          if options
+            if options.key?(:default)
+              default = options[:default]
+              if !default.instance_of?(String)
+                # Call #to_s since all defaults are strings in the descriptor.
+                default = default.to_s
+              end
+              # XXX: we should be C-escaping bytes defaults.
+              field_proto.default_value = default.force_encoding("UTF-8")
+            end
+            if options.key?(:json_name)
+              field_proto.json_name = options[:json_name]
+            end
+          end
+
+          @msg_proto.field << field_proto
+        end
+
+        def internal_msg_proto
+          @msg_proto
+        end
+      end
+
+      class OneofBuilder
+        def initialize(name, msg_builder)
+          @msg_builder = msg_builder
+          oneof_proto = Google::Protobuf::OneofDescriptorProto.new(
+            :name => name
+          )
+          msg_proto = msg_builder.internal_msg_proto
+          @oneof_index = msg_proto.oneof_decl.size
+          msg_proto.oneof_decl << oneof_proto
+        end
+
+        def optional(name, type, number, type_class=nil, options=nil)
+          @msg_builder.internal_add_field(
+              :LABEL_OPTIONAL, name, type, number, type_class, options,
+              oneof_index: @oneof_index)
+        end
+      end
+
+      class EnumBuilder
+        def initialize(name, file_proto)
+          @enum_proto = Google::Protobuf::EnumDescriptorProto.new(
+            :name => name
+          )
+          file_proto.enum_type << @enum_proto
+        end
+
+        def value(name, number)
+          enum_value_proto = Google::Protobuf::EnumValueDescriptorProto.new(
+            name: name,
+            number: number
+          )
+          @enum_proto.value << enum_value_proto
+        end
+      end
+
+    end
+
+    # Re-open the class (the rest of the class is implemented in C)
+    class DescriptorPool
+      def build(&block)
+        builder = Internal::Builder.new(self)
+        builder.instance_eval(&block)
+        builder.build
+      end
+    end
+  end
+end
diff --git a/src/google/protobuf/compiler/ruby/ruby_generator.cc b/src/google/protobuf/compiler/ruby/ruby_generator.cc
index cca69de..8345df2 100644
--- a/src/google/protobuf/compiler/ruby/ruby_generator.cc
+++ b/src/google/protobuf/compiler/ruby/ruby_generator.cc
@@ -527,34 +527,15 @@
   }
 }
 
-bool GenerateFile(const FileDescriptor* file, io::Printer* printer,
-                  std::string* error) {
-  printer->Print(
-    "# Generated by the protocol buffer compiler.  DO NOT EDIT!\n"
-    "# source: $filename$\n"
-    "\n",
-    "filename", file->name());
-
+bool GenerateDSLDescriptor(const FileDescriptor* file, io::Printer* printer,
+                           std::string* error) {
   printer->Print(
     "require 'google/protobuf'\n\n");
-
-  for (int i = 0; i < file->dependency_count(); i++) {
-    if (!MaybeEmitDependency(file->dependency(i), file, printer, error)) {
-      return false;
-    }
-  }
-
-  // TODO: Remove this when ruby supports extensions for proto2 syntax.
-  if (file->syntax() == FileDescriptor::SYNTAX_PROTO2 &&
-      file->extension_count() > 0) {
-    GOOGLE_LOG(WARNING) << "Extensions are not yet supported for proto2 .proto files.";
-  }
-
   printer->Print("Google::Protobuf::DescriptorPool.generated_pool.build do\n");
   printer->Indent();
   printer->Print("add_file(\"$filename$\", :syntax => :$syntax$) do\n",
-		 "filename", file->name(), "syntax",
-		 StringifySyntax(file->syntax()));
+                 "filename", file->name(), "syntax",
+                 StringifySyntax(file->syntax()));
   printer->Indent();
   for (int i = 0; i < file->message_type_count(); i++) {
     if (!GenerateMessage(file->message_type(i), printer, error)) {
@@ -569,6 +550,46 @@
   printer->Outdent();
   printer->Print(
     "end\n\n");
+  return true;
+}
+
+bool GenerateBinaryDescriptor(const FileDescriptor* file, io::Printer* printer,
+                              std::string* error) {
+  FileDescriptorProto file_proto;
+  file->CopyTo(&file_proto);
+  std::string file_data;
+  file_proto.SerializeToString(&file_data);
+
+  printer->Print("Google::Protobuf::DescriptorPool.generated_pool.add_serialized_file(\n");
+  printer->Print("\"$str$\")\n\n", "str", CEscape(file_data));
+  return true;
+}
+
+bool GenerateFile(const FileDescriptor* file, io::Printer* printer,
+                  std::string* error) {
+  printer->Print(
+    "# Generated by the protocol buffer compiler.  DO NOT EDIT!\n"
+    "# source: $filename$\n"
+    "\n",
+    "filename", file->name());
+
+  for (int i = 0; i < file->dependency_count(); i++) {
+    if (!MaybeEmitDependency(file->dependency(i), file, printer, error)) {
+      return false;
+    }
+  }
+
+  // TODO: Remove this when ruby supports extensions for proto2 syntax.
+  if (file->syntax() == FileDescriptor::SYNTAX_PROTO2 &&
+      file->extension_count() > 0) {
+    GOOGLE_LOG(WARNING) << "Extensions are not yet supported for proto2 .proto files.";
+  }
+
+  if (file->name() == "google/protobuf/descriptor.proto") {
+    GenerateBinaryDescriptor(file, printer, error);
+  } else {
+    GenerateDSLDescriptor(file, printer, error);
+  }
 
   int levels = GeneratePackageModules(file, printer);
   for (int i = 0; i < file->message_type_count(); i++) {