Update //third_party/protobuf to version 3.

third_party/protobuf/ruby/ext/google/protobuf_c/defs.c

+// Protocol Buffers - Google's data interchange format
+// Copyright 2014 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#include "protobuf.h"
+
+// -----------------------------------------------------------------------------
+// Common utilities.
+// -----------------------------------------------------------------------------
+
+static const char* get_str(VALUE str) {
+  Check_Type(str, T_STRING);
+  return RSTRING_PTR(str);
+}
+
+static VALUE rb_str_maybe_null(const char* s) {
+  if (s == NULL) {
+    s = "";
+  }
+  return rb_str_new2(s);
+}
+
+static upb_def* check_notfrozen(const upb_def* def) {
+  if (upb_def_isfrozen(def)) {
+    rb_raise(rb_eRuntimeError,
+             "Attempt to modify a frozen descriptor. Once descriptors are "
+             "added to the descriptor pool, they may not be modified.");
+  }
+  return (upb_def*)def;
+}
+
+static upb_msgdef* check_msg_notfrozen(const upb_msgdef* def) {
+  return upb_downcast_msgdef_mutable(check_notfrozen((const upb_def*)def));
+}
+
+static upb_fielddef* check_field_notfrozen(const upb_fielddef* def) {
+  return upb_downcast_fielddef_mutable(check_notfrozen((const upb_def*)def));
+}
+
+static upb_oneofdef* check_oneof_notfrozen(const upb_oneofdef* def) {
+  return (upb_oneofdef*)check_notfrozen((const upb_def*)def);
+}
+
+static upb_enumdef* check_enum_notfrozen(const upb_enumdef* def) {
+  return (upb_enumdef*)check_notfrozen((const upb_def*)def);
+}
+
+// -----------------------------------------------------------------------------
+// DescriptorPool.
+// -----------------------------------------------------------------------------
+
+#define DEFINE_CLASS(name, string_name)                             \
+    VALUE c ## name;                                                \
+    const rb_data_type_t _ ## name ## _type = {                     \
+      string_name,                                                  \
+      { name ## _mark, name ## _free, NULL },                       \
+    };                                                              \
+    name* ruby_to_ ## name(VALUE val) {                             \
+      name* ret;                                                    \
+      TypedData_Get_Struct(val, name, &_ ## name ## _type, ret);    \
+      return ret;                                                   \
+    }                                                               \
+
+#define DEFINE_SELF(type, var, rb_var)                              \
+    type* var = ruby_to_ ## type(rb_var)
+
+// Global singleton DescriptorPool. The user is free to create others, but this
+// is used by generated code.
+VALUE generated_pool;
+
+DEFINE_CLASS(DescriptorPool, "Google::Protobuf::DescriptorPool");
+
+void DescriptorPool_mark(void* _self) {
+}
+
+void DescriptorPool_free(void* _self) {
+  DescriptorPool* self = _self;
+  upb_symtab_unref(self->symtab, &self->symtab);
+  xfree(self);
+}
+
+/*
+ * call-seq:
+ *     DescriptorPool.new => pool
+ *
+ * Creates a new, empty, descriptor pool.
+ */
+VALUE DescriptorPool_alloc(VALUE klass) {
+  DescriptorPool* self = ALLOC(DescriptorPool);
+  self->symtab = upb_symtab_new(&self->symtab);
+  return TypedData_Wrap_Struct(klass, &_DescriptorPool_type, self);
+}
+
+void DescriptorPool_register(VALUE module) {
+  VALUE klass = rb_define_class_under(
+      module, "DescriptorPool", rb_cObject);
+  rb_define_alloc_func(klass, DescriptorPool_alloc);
+  rb_define_method(klass, "add", DescriptorPool_add, 1);
+  rb_define_method(klass, "build", DescriptorPool_build, 0);
+  rb_define_method(klass, "lookup", DescriptorPool_lookup, 1);
+  rb_define_singleton_method(klass, "generated_pool",
+                             DescriptorPool_generated_pool, 0);
+  cDescriptorPool = klass;
+  rb_gc_register_address(&cDescriptorPool);
+
+  generated_pool = rb_class_new_instance(0, NULL, klass);
+  rb_gc_register_address(&generated_pool);
+}
+
+static void add_descriptor_to_pool(DescriptorPool* self,
+                                   Descriptor* descriptor) {
+  CHECK_UPB(
+      upb_symtab_add(self->symtab, (upb_def**)&descriptor->msgdef, 1,
+                     NULL, &status),
+      "Adding Descriptor to DescriptorPool failed");
+}
+
+static void add_enumdesc_to_pool(DescriptorPool* self,
+                                 EnumDescriptor* enumdesc) {
+  CHECK_UPB(
+      upb_symtab_add(self->symtab, (upb_def**)&enumdesc->enumdef, 1,
+                     NULL, &status),
+      "Adding EnumDescriptor to DescriptorPool failed");
+}
+
+/*
+ * call-seq:
+ *     DescriptorPool.add(descriptor)
+ *
+ * Adds the given Descriptor or EnumDescriptor to this pool. All references to
+ * other types in a Descriptor's fields must be resolvable within this pool or
+ * an exception will be raised.
+ */
+VALUE DescriptorPool_add(VALUE _self, VALUE def) {
+  DEFINE_SELF(DescriptorPool, self, _self);
+  VALUE def_klass = rb_obj_class(def);
+  if (def_klass == cDescriptor) {
+    add_descriptor_to_pool(self, ruby_to_Descriptor(def));
+  } else if (def_klass == cEnumDescriptor) {
+    add_enumdesc_to_pool(self, ruby_to_EnumDescriptor(def));
+  } else {
+    rb_raise(rb_eArgError,
+             "Second argument must be a Descriptor or EnumDescriptor.");
+  }
+  return Qnil;
+}
+
+/*
+ * 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.
+ */
+VALUE DescriptorPool_build(VALUE _self) {
+  VALUE ctx = rb_class_new_instance(0, NULL, cBuilder);
+  VALUE block = rb_block_proc();
+  rb_funcall_with_block(ctx, rb_intern("instance_eval"), 0, NULL, block);
+  rb_funcall(ctx, rb_intern("finalize_to_pool"), 1, _self);
+  return Qnil;
+}
+
+/*
+ * call-seq:
+ *     DescriptorPool.lookup(name) => descriptor
+ *
+ * Finds a Descriptor or EnumDescriptor by name and returns it, or nil if none
+ * exists with the given name.
+ */
+VALUE DescriptorPool_lookup(VALUE _self, VALUE name) {
+  DEFINE_SELF(DescriptorPool, self, _self);
+  const char* name_str = get_str(name);
+  const upb_def* def = upb_symtab_lookup(self->symtab, name_str);
+  if (!def) {
+    return Qnil;
+  }
+  return get_def_obj(def);
+}
+
+/*
+ * call-seq:
+ *     DescriptorPool.generated_pool => descriptor_pool
+ *
+ * Class method that returns the global DescriptorPool. This is a singleton into
+ * which generated-code message and enum types are registered. The user may also
+ * register types in this pool for convenience so that they do not have to hold
+ * a reference to a private pool instance.
+ */
+VALUE DescriptorPool_generated_pool(VALUE _self) {
+  return generated_pool;
+}
+
+// -----------------------------------------------------------------------------
+// Descriptor.
+// -----------------------------------------------------------------------------
+
+DEFINE_CLASS(Descriptor, "Google::Protobuf::Descriptor");
+
+void Descriptor_mark(void* _self) {
+  Descriptor* self = _self;
+  rb_gc_mark(self->klass);
+  rb_gc_mark(self->typeclass_references);
+}
+
+void Descriptor_free(void* _self) {
+  Descriptor* self = _self;
+  upb_msgdef_unref(self->msgdef, &self->msgdef);
+  if (self->layout) {
+    free_layout(self->layout);
+  }
+  if (self->fill_handlers) {
+    upb_handlers_unref(self->fill_handlers, &self->fill_handlers);
+  }
+  if (self->fill_method) {
+    upb_pbdecodermethod_unref(self->fill_method, &self->fill_method);
+  }
+  if (self->pb_serialize_handlers) {
+    upb_handlers_unref(self->pb_serialize_handlers,
+                       &self->pb_serialize_handlers);
+  }
+  if (self->json_serialize_handlers) {
+    upb_handlers_unref(self->json_serialize_handlers,
+                       &self->json_serialize_handlers);
+  }
+  xfree(self);
+}
+
+/*
+ * call-seq:
+ *     Descriptor.new => descriptor
+ *
+ * Creates a new, empty, message type descriptor. At a minimum, its name must be
+ * set before it is added to a pool. It cannot be used to create messages until
+ * it is added to a pool, after which it becomes immutable (as part of a
+ * finalization process).
+ */
+VALUE Descriptor_alloc(VALUE klass) {
+  Descriptor* self = ALLOC(Descriptor);
+  VALUE ret = TypedData_Wrap_Struct(klass, &_Descriptor_type, self);
+  self->msgdef = upb_msgdef_new(&self->msgdef);
+  self->klass = Qnil;
+  self->layout = NULL;
+  self->fill_handlers = NULL;
+  self->fill_method = NULL;
+  self->pb_serialize_handlers = NULL;
+  self->json_serialize_handlers = NULL;
+  self->typeclass_references = rb_ary_new();
+  return ret;
+}
+
+void Descriptor_register(VALUE module) {
+  VALUE klass = rb_define_class_under(
+      module, "Descriptor", rb_cObject);
+  rb_define_alloc_func(klass, Descriptor_alloc);
+  rb_define_method(klass, "each", Descriptor_each, 0);
+  rb_define_method(klass, "lookup", Descriptor_lookup, 1);
+  rb_define_method(klass, "add_field", Descriptor_add_field, 1);
+  rb_define_method(klass, "add_oneof", Descriptor_add_oneof, 1);
+  rb_define_method(klass, "each_oneof", Descriptor_each_oneof, 0);
+  rb_define_method(klass, "lookup_oneof", Descriptor_lookup_oneof, 1);
+  rb_define_method(klass, "msgclass", Descriptor_msgclass, 0);
+  rb_define_method(klass, "name", Descriptor_name, 0);
+  rb_define_method(klass, "name=", Descriptor_name_set, 1);
+  rb_include_module(klass, rb_mEnumerable);
+  cDescriptor = klass;
+  rb_gc_register_address(&cDescriptor);
+}
+
+/*
+ * call-seq:
+ *     Descriptor.name => name
+ *
+ * Returns the name of this message type as a fully-qualfied string (e.g.,
+ * My.Package.MessageType).
+ */
+VALUE Descriptor_name(VALUE _self) {
+  DEFINE_SELF(Descriptor, self, _self);
+  return rb_str_maybe_null(upb_msgdef_fullname(self->msgdef));
+}
+
+/*
+ * call-seq:
+ *    Descriptor.name = name
+ *
+ * Assigns a name to this message type. The descriptor must not have been added
+ * to a pool yet.
+ */
+VALUE Descriptor_name_set(VALUE _self, VALUE str) {
+  DEFINE_SELF(Descriptor, self, _self);
+  upb_msgdef* mut_def = check_msg_notfrozen(self->msgdef);
+  const char* name = get_str(str);
+  CHECK_UPB(
+      upb_msgdef_setfullname(mut_def, name, &status),
+      "Error setting Descriptor name");
+  return Qnil;
+}
+
+/*
+ * call-seq:
+ *     Descriptor.each(&block)
+ *
+ * Iterates over fields in this message type, yielding to the block on each one.
+ */
+VALUE Descriptor_each(VALUE _self) {
+  DEFINE_SELF(Descriptor, self, _self);
+
+  upb_msg_field_iter it;
+  for (upb_msg_field_begin(&it, self->msgdef);
+       !upb_msg_field_done(&it);
+       upb_msg_field_next(&it)) {
+    const upb_fielddef* field = upb_msg_iter_field(&it);
+    VALUE obj = get_def_obj(field);
+    rb_yield(obj);
+  }
+  return Qnil;
+}
+
+/*
+ * call-seq:
+ *     Descriptor.lookup(name) => FieldDescriptor
+ *
+ * Returns the field descriptor for the field with the given name, if present,
+ * or nil if none.
+ */
+VALUE Descriptor_lookup(VALUE _self, VALUE name) {
+  DEFINE_SELF(Descriptor, self, _self);
+  const char* s = get_str(name);
+  const upb_fielddef* field = upb_msgdef_ntofz(self->msgdef, s);
+  if (field == NULL) {
+    return Qnil;
+  }
+  return get_def_obj(field);
+}
+
+/*
+ * call-seq:
+ *     Descriptor.add_field(field) => nil
+ *
+ * Adds the given FieldDescriptor to this message type. This descriptor must not
+ * have been added to a pool yet. Raises an exception if a field with the same
+ * name or number already exists. Sub-type references (e.g. for fields of type
+ * message) are not resolved at this point.
+ */
+VALUE Descriptor_add_field(VALUE _self, VALUE obj) {
+  DEFINE_SELF(Descriptor, self, _self);
+  upb_msgdef* mut_def = check_msg_notfrozen(self->msgdef);
+  FieldDescriptor* def = ruby_to_FieldDescriptor(obj);
+  upb_fielddef* mut_field_def = check_field_notfrozen(def->fielddef);
+  CHECK_UPB(
+      upb_msgdef_addfield(mut_def, mut_field_def, NULL, &status),
+      "Adding field to Descriptor failed");
+  add_def_obj(def->fielddef, obj);
+  return Qnil;
+}
+
+/*
+ * call-seq:
+ *     Descriptor.add_oneof(oneof) => nil
+ *
+ * Adds the given OneofDescriptor to this message type. This descriptor must not
+ * have been added to a pool yet. Raises an exception if a oneof with the same
+ * name already exists, or if any of the oneof's fields' names or numbers
+ * conflict with an existing field in this message type. All fields in the oneof
+ * are added to the message descriptor. Sub-type references (e.g. for fields of
+ * type message) are not resolved at this point.
+ */
+VALUE Descriptor_add_oneof(VALUE _self, VALUE obj) {
+  DEFINE_SELF(Descriptor, self, _self);
+  upb_msgdef* mut_def = check_msg_notfrozen(self->msgdef);
+  OneofDescriptor* def = ruby_to_OneofDescriptor(obj);
+  upb_oneofdef* mut_oneof_def = check_oneof_notfrozen(def->oneofdef);
+  CHECK_UPB(
+      upb_msgdef_addoneof(mut_def, mut_oneof_def, NULL, &status),
+      "Adding oneof to Descriptor failed");
+  add_def_obj(def->oneofdef, obj);
+  return Qnil;
+}
+
+/*
+ * call-seq:
+ *     Descriptor.each_oneof(&block) => nil
+ *
+ * Invokes the given block for each oneof in this message type, passing the
+ * corresponding OneofDescriptor.
+ */
+VALUE Descriptor_each_oneof(VALUE _self) {
+  DEFINE_SELF(Descriptor, self, _self);
+
+  upb_msg_oneof_iter it;
+  for (upb_msg_oneof_begin(&it, self->msgdef);
+       !upb_msg_oneof_done(&it);
+       upb_msg_oneof_next(&it)) {
+    const upb_oneofdef* oneof = upb_msg_iter_oneof(&it);
+    VALUE obj = get_def_obj(oneof);
+    rb_yield(obj);
+  }
+  return Qnil;
+}
+
+/*
+ * call-seq:
+ *     Descriptor.lookup_oneof(name) => OneofDescriptor
+ *
+ * Returns the oneof descriptor for the oneof with the given name, if present,
+ * or nil if none.
+ */
+VALUE Descriptor_lookup_oneof(VALUE _self, VALUE name) {
+  DEFINE_SELF(Descriptor, self, _self);
+  const char* s = get_str(name);
+  const upb_oneofdef* oneof = upb_msgdef_ntooz(self->msgdef, s);
+  if (oneof == NULL) {
+    return Qnil;
+  }
+  return get_def_obj(oneof);
+}
+
+/*
+ * call-seq:
+ *     Descriptor.msgclass => message_klass
+ *
+ * Returns the Ruby class created for this message type. Valid only once the
+ * message type has been added to a pool.
+ */
+VALUE Descriptor_msgclass(VALUE _self) {
+  DEFINE_SELF(Descriptor, self, _self);
+  if (!upb_def_isfrozen((const upb_def*)self->msgdef)) {
+    rb_raise(rb_eRuntimeError,
+             "Cannot fetch message class from a Descriptor not yet in a pool.");
+  }
+  if (self->klass == Qnil) {
+    self->klass = build_class_from_descriptor(self);
+  }
+  return self->klass;
+}
+
+// -----------------------------------------------------------------------------
+// FieldDescriptor.
+// -----------------------------------------------------------------------------
+
+DEFINE_CLASS(FieldDescriptor, "Google::Protobuf::FieldDescriptor");
+
+void FieldDescriptor_mark(void* _self) {
+}
+
+void FieldDescriptor_free(void* _self) {
+  FieldDescriptor* self = _self;
+  upb_fielddef_unref(self->fielddef, &self->fielddef);
+  xfree(self);
+}
+
+/*
+ * call-seq:
+ *     FieldDescriptor.new => field
+ *
+ * Returns a new field descriptor. Its name, type, etc. must be set before it is
+ * added to a message type.
+ */
+VALUE FieldDescriptor_alloc(VALUE klass) {
+  FieldDescriptor* self = ALLOC(FieldDescriptor);
+  VALUE ret = TypedData_Wrap_Struct(klass, &_FieldDescriptor_type, self);
+  upb_fielddef* fielddef = upb_fielddef_new(&self->fielddef);
+  upb_fielddef_setpacked(fielddef, false);
+  self->fielddef = fielddef;
+  return ret;
+}
+
+void FieldDescriptor_register(VALUE module) {
+  VALUE klass = rb_define_class_under(
+      module, "FieldDescriptor", rb_cObject);
+  rb_define_alloc_func(klass, FieldDescriptor_alloc);
+  rb_define_method(klass, "name", FieldDescriptor_name, 0);
+  rb_define_method(klass, "name=", FieldDescriptor_name_set, 1);
+  rb_define_method(klass, "type", FieldDescriptor_type, 0);
+  rb_define_method(klass, "type=", FieldDescriptor_type_set, 1);
+  rb_define_method(klass, "label", FieldDescriptor_label, 0);
+  rb_define_method(klass, "label=", FieldDescriptor_label_set, 1);
+  rb_define_method(klass, "number", FieldDescriptor_number, 0);
+  rb_define_method(klass, "number=", FieldDescriptor_number_set, 1);
+  rb_define_method(klass, "submsg_name", FieldDescriptor_submsg_name, 0);
+  rb_define_method(klass, "submsg_name=", FieldDescriptor_submsg_name_set, 1);
+  rb_define_method(klass, "subtype", FieldDescriptor_subtype, 0);
+  rb_define_method(klass, "get", FieldDescriptor_get, 1);
+  rb_define_method(klass, "set", FieldDescriptor_set, 2);
+  cFieldDescriptor = klass;
+  rb_gc_register_address(&cFieldDescriptor);
+}
+
+/*
+ * call-seq:
+ *     FieldDescriptor.name => name
+ *
+ * Returns the name of this field.
+ */
+VALUE FieldDescriptor_name(VALUE _self) {
+  DEFINE_SELF(FieldDescriptor, self, _self);
+  return rb_str_maybe_null(upb_fielddef_name(self->fielddef));
+}
+
+/*
+ * call-seq:
+ *     FieldDescriptor.name = name
+ *
+ * Sets the name of this field. Cannot be called once the containing message
+ * type, if any, is added to a pool.
+ */
+VALUE FieldDescriptor_name_set(VALUE _self, VALUE str) {
+  DEFINE_SELF(FieldDescriptor, self, _self);
+  upb_fielddef* mut_def = check_field_notfrozen(self->fielddef);
+  const char* name = get_str(str);
+  CHECK_UPB(upb_fielddef_setname(mut_def, name, &status),
+            "Error setting FieldDescriptor name");
+  return Qnil;
+}
+
+upb_fieldtype_t ruby_to_fieldtype(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_TYPE_ ## upb;                                         \
+  }
+
+  CONVERT(FLOAT, float);
+  CONVERT(DOUBLE, double);
+  CONVERT(BOOL, bool);
+  CONVERT(STRING, string);
+  CONVERT(BYTES, bytes);
+  CONVERT(MESSAGE, message);
+  CONVERT(ENUM, enum);
+  CONVERT(INT32, int32);
+  CONVERT(INT64, int64);
+  CONVERT(UINT32, uint32);
+  CONVERT(UINT64, uint64);
+
+#undef CONVERT
+
+  rb_raise(rb_eArgError, "Unknown field type.");
+  return 0;
+}
+
+VALUE fieldtype_to_ruby(upb_fieldtype_t type) {
+  switch (type) {
+#define CONVERT(upb, ruby)                                           \
+    case UPB_TYPE_ ## upb : return ID2SYM(rb_intern( # ruby ));
+    CONVERT(FLOAT, float);
+    CONVERT(DOUBLE, double);
+    CONVERT(BOOL, bool);
+    CONVERT(STRING, string);
+    CONVERT(BYTES, bytes);
+    CONVERT(MESSAGE, message);
+    CONVERT(ENUM, enum);
+    CONVERT(INT32, int32);
+    CONVERT(INT64, int64);
+    CONVERT(UINT32, uint32);
+    CONVERT(UINT64, uint64);
+#undef CONVERT
+  }
+  return Qnil;
+}
+
+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;
+}
+
+VALUE descriptortype_to_ruby(upb_descriptortype_t type) {
+  switch (type) {
+#define CONVERT(upb, ruby)                                           \
+    case UPB_DESCRIPTOR_TYPE_ ## upb : return ID2SYM(rb_intern( # ruby ));
+    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
+  }
+  return Qnil;
+}
+
+/*
+ * call-seq:
+ *     FieldDescriptor.type => type
+ *
+ * Returns this field's type, as a Ruby symbol, or nil if not yet set.
+ *
+ * Valid field types are:
+ *     :int32, :int64, :uint32, :uint64, :float, :double, :bool, :string,
+ *     :bytes, :message.
+ */
+VALUE FieldDescriptor_type(VALUE _self) {
+  DEFINE_SELF(FieldDescriptor, self, _self);
+  if (!upb_fielddef_typeisset(self->fielddef)) {
+    return Qnil;
+  }
+  return descriptortype_to_ruby(upb_fielddef_descriptortype(self->fielddef));
+}
+
+/*
+ * call-seq:
+ *     FieldDescriptor.type = type
+ *
+ * Sets this field's type. Cannot be called if field is part of a message type
+ * already in a pool.
+ */
+VALUE FieldDescriptor_type_set(VALUE _self, VALUE type) {
+  DEFINE_SELF(FieldDescriptor, self, _self);
+  upb_fielddef* mut_def = check_field_notfrozen(self->fielddef);
+  upb_fielddef_setdescriptortype(mut_def, ruby_to_descriptortype(type));
+  return Qnil;
+}
+
+/*
+ * call-seq:
+ *     FieldDescriptor.label => label
+ *
+ * Returns this field's label (i.e., plurality), as a Ruby symbol.
+ *
+ * Valid field labels are:
+ *     :optional, :repeated
+ */
+VALUE FieldDescriptor_label(VALUE _self) {
+  DEFINE_SELF(FieldDescriptor, self, _self);
+  switch (upb_fielddef_label(self->fielddef)) {
+#define CONVERT(upb, ruby)                                           \
+    case UPB_LABEL_ ## upb : return ID2SYM(rb_intern( # ruby ));
+
+    CONVERT(OPTIONAL, optional);
+    CONVERT(REQUIRED, required);
+    CONVERT(REPEATED, repeated);
+
+#undef CONVERT
+  }
+
+  return Qnil;
+}
+
+/*
+ * call-seq:
+ *     FieldDescriptor.label = label
+ *
+ * Sets the label on this field. Cannot be called if field is part of a message
+ * type already in a pool.
+ */
+VALUE FieldDescriptor_label_set(VALUE _self, VALUE label) {
+  DEFINE_SELF(FieldDescriptor, self, _self);
+  upb_fielddef* mut_def = check_field_notfrozen(self->fielddef);
+  upb_label_t upb_label = -1;
+  bool converted = false;
+
+  if (TYPE(label) != T_SYMBOL) {
+    rb_raise(rb_eArgError, "Expected symbol for field label.");
+  }
+
+#define CONVERT(upb, ruby)                                           \
+  if (SYM2ID(label) == rb_intern( # ruby )) {                        \
+    upb_label = UPB_LABEL_ ## upb;                                   \
+    converted = true;                                                \
+  }
+
+  CONVERT(OPTIONAL, optional);
+  CONVERT(REQUIRED, required);
+  CONVERT(REPEATED, repeated);
+
+#undef CONVERT
+
+  if (!converted) {
+    rb_raise(rb_eArgError, "Unknown field label.");
+  }
+
+  upb_fielddef_setlabel(mut_def, upb_label);
+
+  return Qnil;
+}
+
+/*
+ * call-seq:
+ *     FieldDescriptor.number => number
+ *
+ * Returns the tag number for this field.
+ */
+VALUE FieldDescriptor_number(VALUE _self) {
+  DEFINE_SELF(FieldDescriptor, self, _self);
+  return INT2NUM(upb_fielddef_number(self->fielddef));
+}
+
+/*
+ * call-seq:
+ *     FieldDescriptor.number = number
+ *
+ * Sets the tag number for this field. Cannot be called if field is part of a
+ * message type already in a pool.
+ */
+VALUE FieldDescriptor_number_set(VALUE _self, VALUE number) {
+  DEFINE_SELF(FieldDescriptor, self, _self);
+  upb_fielddef* mut_def = check_field_notfrozen(self->fielddef);
+  CHECK_UPB(upb_fielddef_setnumber(mut_def, NUM2INT(number), &status),
+            "Error setting field number");
+  return Qnil;
+}
+
+/*
+ * call-seq:
+ *     FieldDescriptor.submsg_name => submsg_name
+ *
+ * Returns the name of the message or enum type corresponding to this field, if
+ * it is a message or enum field (respectively), or nil otherwise. This type
+ * name will be resolved within the context of the pool to which the containing
+ * message type is added.
+ */
+VALUE FieldDescriptor_submsg_name(VALUE _self) {
+  DEFINE_SELF(FieldDescriptor, self, _self);
+  if (!upb_fielddef_hassubdef(self->fielddef)) {
+    return Qnil;
+  }
+  return rb_str_maybe_null(upb_fielddef_subdefname(self->fielddef));
+}
+
+/*
+ * call-seq:
+ *     FieldDescriptor.submsg_name = submsg_name
+ *
+ * Sets the name of the message or enum type corresponding to this field, if it
+ * is a message or enum field (respectively). This type name will be resolved
+ * within the context of the pool to which the containing message type is added.
+ * Cannot be called on field that are not of message or enum type, or on fields
+ * that are part of a message type already added to a pool.
+ */
+VALUE FieldDescriptor_submsg_name_set(VALUE _self, VALUE value) {
+  DEFINE_SELF(FieldDescriptor, self, _self);
+  upb_fielddef* mut_def = check_field_notfrozen(self->fielddef);
+  const char* str = get_str(value);
+  if (!upb_fielddef_hassubdef(self->fielddef)) {
+    rb_raise(rb_eTypeError, "FieldDescriptor does not have subdef.");
+  }
+  CHECK_UPB(upb_fielddef_setsubdefname(mut_def, str, &status),
+            "Error setting submessage name");
+  return Qnil;
+}
+
+/*
+ * call-seq:
+ *     FieldDescriptor.subtype => message_or_enum_descriptor
+ *
+ * Returns the message or enum descriptor corresponding to this field's type if
+ * it is a message or enum field, respectively, or nil otherwise. Cannot be
+ * called *until* the containing message type is added to a pool (and thus
+ * resolved).
+ */
+VALUE FieldDescriptor_subtype(VALUE _self) {
+  DEFINE_SELF(FieldDescriptor, self, _self);
+  const upb_def* def;
+
+  if (!upb_fielddef_hassubdef(self->fielddef)) {
+    return Qnil;
+  }
+  def = upb_fielddef_subdef(self->fielddef);
+  if (def == NULL) {
+    return Qnil;
+  }
+  return get_def_obj(def);
+}
+
+/*
+ * call-seq:
+ *     FieldDescriptor.get(message) => value
+ *
+ * Returns the value set for this field on the given message. Raises an
+ * exception if message is of the wrong type.
+ */
+VALUE FieldDescriptor_get(VALUE _self, VALUE msg_rb) {
+  DEFINE_SELF(FieldDescriptor, self, _self);
+  MessageHeader* msg;
+  TypedData_Get_Struct(msg_rb, MessageHeader, &Message_type, msg);
+  if (msg->descriptor->msgdef != upb_fielddef_containingtype(self->fielddef)) {
+    rb_raise(rb_eTypeError, "get method called on wrong message type");
+  }
+  return layout_get(msg->descriptor->layout, Message_data(msg), self->fielddef);
+}
+
+/*
+ * call-seq:
+ *     FieldDescriptor.set(message, value)
+ *
+ * Sets the value corresponding to this field to the given value on the given
+ * message. Raises an exception if message is of the wrong type. Performs the
+ * ordinary type-checks for field setting.
+ */
+VALUE FieldDescriptor_set(VALUE _self, VALUE msg_rb, VALUE value) {
+  DEFINE_SELF(FieldDescriptor, self, _self);
+  MessageHeader* msg;
+  TypedData_Get_Struct(msg_rb, MessageHeader, &Message_type, msg);
+  if (msg->descriptor->msgdef != upb_fielddef_containingtype(self->fielddef)) {
+    rb_raise(rb_eTypeError, "set method called on wrong message type");
+  }
+  layout_set(msg->descriptor->layout, Message_data(msg), self->fielddef, value);
+  return Qnil;
+}
+
+// -----------------------------------------------------------------------------
+// OneofDescriptor.
+// -----------------------------------------------------------------------------
+
+DEFINE_CLASS(OneofDescriptor, "Google::Protobuf::OneofDescriptor");
+
+void OneofDescriptor_mark(void* _self) {
+}
+
+void OneofDescriptor_free(void* _self) {
+  OneofDescriptor* self = _self;
+  upb_oneofdef_unref(self->oneofdef, &self->oneofdef);
+  xfree(self);
+}
+
+/*
+ * call-seq:
+ *     OneofDescriptor.new => oneof_descriptor
+ *
+ * Creates a new, empty, oneof descriptor. The oneof may only be modified prior
+ * to being added to a message descriptor which is subsequently added to a pool.
+ */
+VALUE OneofDescriptor_alloc(VALUE klass) {
+  OneofDescriptor* self = ALLOC(OneofDescriptor);
+  VALUE ret = TypedData_Wrap_Struct(klass, &_OneofDescriptor_type, self);
+  self->oneofdef = upb_oneofdef_new(&self->oneofdef);
+  return ret;
+}
+
+void OneofDescriptor_register(VALUE module) {
+  VALUE klass = rb_define_class_under(
+      module, "OneofDescriptor", rb_cObject);
+  rb_define_alloc_func(klass, OneofDescriptor_alloc);
+  rb_define_method(klass, "name", OneofDescriptor_name, 0);
+  rb_define_method(klass, "name=", OneofDescriptor_name_set, 1);
+  rb_define_method(klass, "add_field", OneofDescriptor_add_field, 1);
+  rb_define_method(klass, "each", OneofDescriptor_each, 0);
+  rb_include_module(klass, rb_mEnumerable);
+  cOneofDescriptor = klass;
+  rb_gc_register_address(&cOneofDescriptor);
+}
+
+/*
+ * call-seq:
+ *     OneofDescriptor.name => name
+ *
+ * Returns the name of this oneof.
+ */
+VALUE OneofDescriptor_name(VALUE _self) {
+  DEFINE_SELF(OneofDescriptor, self, _self);
+  return rb_str_maybe_null(upb_oneofdef_name(self->oneofdef));
+}
+
+/*
+ * call-seq:
+ *     OneofDescriptor.name = name
+ *
+ * Sets a new name for this oneof. The oneof must not have been added to a
+ * message descriptor yet.
+ */
+VALUE OneofDescriptor_name_set(VALUE _self, VALUE value) {
+  DEFINE_SELF(OneofDescriptor, self, _self);
+  upb_oneofdef* mut_def = check_oneof_notfrozen(self->oneofdef);
+  const char* str = get_str(value);
+  CHECK_UPB(upb_oneofdef_setname(mut_def, str, &status),
+            "Error setting oneof name");
+  return Qnil;
+}
+
+/*
+ * call-seq:
+ *     OneofDescriptor.add_field(field) => nil
+ *
+ * Adds a field to this oneof. The field may have been added to this oneof in
+ * the past, or the message to which this oneof belongs (if any), but may not
+ * have already been added to any other oneof or message. Otherwise, an
+ * exception is raised.
+ *
+ * All fields added to the oneof via this method will be automatically added to
+ * the message to which this oneof belongs, if it belongs to one currently, or
+ * else will be added to any message to which the oneof is later added at the
+ * time that it is added.
+ */
+VALUE OneofDescriptor_add_field(VALUE _self, VALUE obj) {
+  DEFINE_SELF(OneofDescriptor, self, _self);
+  upb_oneofdef* mut_def = check_oneof_notfrozen(self->oneofdef);
+  FieldDescriptor* def = ruby_to_FieldDescriptor(obj);
+  upb_fielddef* mut_field_def = check_field_notfrozen(def->fielddef);
+  CHECK_UPB(
+      upb_oneofdef_addfield(mut_def, mut_field_def, NULL, &status),
+      "Adding field to OneofDescriptor failed");
+  add_def_obj(def->fielddef, obj);
+  return Qnil;
+}
+
+/*
+ * call-seq:
+ *     OneofDescriptor.each(&block) => nil
+ *
+ * Iterates through fields in this oneof, yielding to the block on each one.
+ */
+VALUE OneofDescriptor_each(VALUE _self, VALUE field) {
+  DEFINE_SELF(OneofDescriptor, self, _self);
+  upb_oneof_iter it;
+  for (upb_oneof_begin(&it, self->oneofdef);
+       !upb_oneof_done(&it);
+       upb_oneof_next(&it)) {
+    const upb_fielddef* f = upb_oneof_iter_field(&it);
+    VALUE obj = get_def_obj(f);
+    rb_yield(obj);
+  }
+  return Qnil;
+}
+
+// -----------------------------------------------------------------------------
+// EnumDescriptor.
+// -----------------------------------------------------------------------------
+
+DEFINE_CLASS(EnumDescriptor, "Google::Protobuf::EnumDescriptor");
+
+void EnumDescriptor_mark(void* _self) {
+  EnumDescriptor* self = _self;
+  rb_gc_mark(self->module);
+}
+
+void EnumDescriptor_free(void* _self) {
+  EnumDescriptor* self = _self;
+  upb_enumdef_unref(self->enumdef, &self->enumdef);
+  xfree(self);
+}
+
+/*
+ * call-seq:
+ *     EnumDescriptor.new => enum_descriptor
+ *
+ * Creates a new, empty, enum descriptor. Must be added to a pool before the
+ * enum type can be used. The enum type may only be modified prior to adding to
+ * a pool.
+ */
+VALUE EnumDescriptor_alloc(VALUE klass) {
+  EnumDescriptor* self = ALLOC(EnumDescriptor);
+  VALUE ret = TypedData_Wrap_Struct(klass, &_EnumDescriptor_type, self);
+  self->enumdef = upb_enumdef_new(&self->enumdef);
+  self->module = Qnil;
+  return ret;
+}
+
+void EnumDescriptor_register(VALUE module) {
+  VALUE klass = rb_define_class_under(
+      module, "EnumDescriptor", rb_cObject);
+  rb_define_alloc_func(klass, EnumDescriptor_alloc);
+  rb_define_method(klass, "name", EnumDescriptor_name, 0);
+  rb_define_method(klass, "name=", EnumDescriptor_name_set, 1);
+  rb_define_method(klass, "add_value", EnumDescriptor_add_value, 2);
+  rb_define_method(klass, "lookup_name", EnumDescriptor_lookup_name, 1);
+  rb_define_method(klass, "lookup_value", EnumDescriptor_lookup_value, 1);
+  rb_define_method(klass, "each", EnumDescriptor_each, 0);
+  rb_define_method(klass, "enummodule", EnumDescriptor_enummodule, 0);
+  rb_include_module(klass, rb_mEnumerable);
+  cEnumDescriptor = klass;
+  rb_gc_register_address(&cEnumDescriptor);
+}
+
+/*
+ * call-seq:
+ *     EnumDescriptor.name => name
+ *
+ * Returns the name of this enum type.
+ */
+VALUE EnumDescriptor_name(VALUE _self) {
+  DEFINE_SELF(EnumDescriptor, self, _self);
+  return rb_str_maybe_null(upb_enumdef_fullname(self->enumdef));
+}
+
+/*
+ * call-seq:
+ *     EnumDescriptor.name = name
+ *
+ * Sets the name of this enum type. Cannot be called if the enum type has
+ * already been added to a pool.
+ */
+VALUE EnumDescriptor_name_set(VALUE _self, VALUE str) {
+  DEFINE_SELF(EnumDescriptor, self, _self);
+  upb_enumdef* mut_def = check_enum_notfrozen(self->enumdef);
+  const char* name = get_str(str);
+  CHECK_UPB(upb_enumdef_setfullname(mut_def, name, &status),
+            "Error setting EnumDescriptor name");
+  return Qnil;
+}
+
+/*
+ * call-seq:
+ *     EnumDescriptor.add_value(key, value)
+ *
+ * Adds a new key => value mapping to this enum type. Key must be given as a
+ * Ruby symbol. Cannot be called if the enum type has already been added to a
+ * pool. Will raise an exception if the key or value is already in use.
+ */
+VALUE EnumDescriptor_add_value(VALUE _self, VALUE name, VALUE number) {
+  DEFINE_SELF(EnumDescriptor, self, _self);
+  upb_enumdef* mut_def = check_enum_notfrozen(self->enumdef);
+  const char* name_str = rb_id2name(SYM2ID(name));
+  int32_t val = NUM2INT(number);
+  CHECK_UPB(upb_enumdef_addval(mut_def, name_str, val, &status),
+            "Error adding value to enum");
+  return Qnil;
+}
+
+/*
+ * call-seq:
+ *     EnumDescriptor.lookup_name(name) => value
+ *
+ * Returns the numeric value corresponding to the given key name (as a Ruby
+ * symbol), or nil if none.
+ */
+VALUE EnumDescriptor_lookup_name(VALUE _self, VALUE name) {
+  DEFINE_SELF(EnumDescriptor, self, _self);
+  const char* name_str= rb_id2name(SYM2ID(name));
+  int32_t val = 0;
+  if (upb_enumdef_ntoiz(self->enumdef, name_str, &val)) {
+    return INT2NUM(val);
+  } else {
+    return Qnil;
+  }
+}
+
+/*
+ * call-seq:
+ *     EnumDescriptor.lookup_value(name) => value
+ *
+ * Returns the key name (as a Ruby symbol) corresponding to the integer value,
+ * or nil if none.
+ */
+VALUE EnumDescriptor_lookup_value(VALUE _self, VALUE number) {
+  DEFINE_SELF(EnumDescriptor, self, _self);
+  int32_t val = NUM2INT(number);
+  const char* name = upb_enumdef_iton(self->enumdef, val);
+  if (name != NULL) {
+    return ID2SYM(rb_intern(name));
+  } else {
+    return Qnil;
+  }
+}
+
+/*
+ * call-seq:
+ *     EnumDescriptor.each(&block)
+ *
+ * Iterates over key => value mappings in this enum's definition, yielding to
+ * the block with (key, value) arguments for each one.
+ */
+VALUE EnumDescriptor_each(VALUE _self) {
+  DEFINE_SELF(EnumDescriptor, self, _self);
+
+  upb_enum_iter it;
+  for (upb_enum_begin(&it, self->enumdef);
+       !upb_enum_done(&it);
+       upb_enum_next(&it)) {
+    VALUE key = ID2SYM(rb_intern(upb_enum_iter_name(&it)));
+    VALUE number = INT2NUM(upb_enum_iter_number(&it));
+    rb_yield_values(2, key, number);
+  }
+
+  return Qnil;
+}
+
+/*
+ * call-seq:
+ *     EnumDescriptor.enummodule => module
+ *
+ * Returns the Ruby module corresponding to this enum type. Cannot be called
+ * until the enum descriptor has been added to a pool.
+ */
+VALUE EnumDescriptor_enummodule(VALUE _self) {
+  DEFINE_SELF(EnumDescriptor, self, _self);
+  if (!upb_def_isfrozen((const upb_def*)self->enumdef)) {
+    rb_raise(rb_eRuntimeError,
+             "Cannot fetch enum module from an EnumDescriptor not yet "
+             "in a pool.");
+  }
+  if (self->module == Qnil) {
+    self->module = build_module_from_enumdesc(self);
+  }
+  return self->module;
+}
+
+// -----------------------------------------------------------------------------
+// MessageBuilderContext.
+// -----------------------------------------------------------------------------
+
+DEFINE_CLASS(MessageBuilderContext,
+    "Google::Protobuf::Internal::MessageBuilderContext");
+
+void MessageBuilderContext_mark(void* _self) {
+  MessageBuilderContext* self = _self;
+  rb_gc_mark(self->descriptor);
+  rb_gc_mark(self->builder);
+}
+
+void MessageBuilderContext_free(void* _self) {
+  MessageBuilderContext* self = _self;
+  xfree(self);
+}
+
+VALUE MessageBuilderContext_alloc(VALUE klass) {
+  MessageBuilderContext* self = ALLOC(MessageBuilderContext);
+  VALUE ret = TypedData_Wrap_Struct(
+      klass, &_MessageBuilderContext_type, self);
+  self->descriptor = Qnil;
+  self->builder = Qnil;
+  return ret;
+}
+
+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, "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);
+  cMessageBuilderContext = klass;
+  rb_gc_register_address(&cMessageBuilderContext);
+}
+
+/*
+ * call-seq:
+ *     MessageBuilderContext.new(desc, builder) => 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.
+ */
+VALUE MessageBuilderContext_initialize(VALUE _self,
+                                       VALUE msgdef,
+                                       VALUE builder) {
+  DEFINE_SELF(MessageBuilderContext, self, _self);
+  self->descriptor = msgdef;
+  self->builder = builder;
+  return Qnil;
+}
+
+static VALUE msgdef_add_field(VALUE msgdef,
+                              const char* label, VALUE name,
+                              VALUE type, VALUE number,
+                              VALUE type_class) {
+  VALUE fielddef = rb_class_new_instance(0, NULL, cFieldDescriptor);
+  VALUE name_str = rb_str_new2(rb_id2name(SYM2ID(name)));
+
+  rb_funcall(fielddef, rb_intern("label="), 1, ID2SYM(rb_intern(label)));
+  rb_funcall(fielddef, rb_intern("name="), 1, name_str);
+  rb_funcall(fielddef, rb_intern("type="), 1, type);
+  rb_funcall(fielddef, rb_intern("number="), 1, number);
+
+  if (type_class != Qnil) {
+    if (TYPE(type_class) != T_STRING) {
+      rb_raise(rb_eArgError, "Expected string for type class");
+    }
+    // Make it an absolute type name by prepending a dot.
+    type_class = rb_str_append(rb_str_new2("."), type_class);
+    rb_funcall(fielddef, rb_intern("submsg_name="), 1, type_class);
+  }
+
+  rb_funcall(msgdef, rb_intern("add_field"), 1, fielddef);
+  return fielddef;
+}
+
+/*
+ * call-seq:
+ *     MessageBuilderContext.optional(name, type, number, type_class = 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) {
+  DEFINE_SELF(MessageBuilderContext, self, _self);
+  VALUE name, type, number, type_class;
+
+  if (argc < 3) {
+    rb_raise(rb_eArgError, "Expected at least 3 arguments.");
+  }
+  name = argv[0];
+  type = argv[1];
+  number = argv[2];
+  type_class = (argc > 3) ? argv[3] : Qnil;
+
+  return msgdef_add_field(self->descriptor, "optional",
+                          name, type, number, type_class);
+}
+
+/*
+ * call-seq:
+ *     MessageBuilderContext.required(name, type, number, type_class = 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.
+ */
+VALUE MessageBuilderContext_required(int argc, VALUE* argv, VALUE _self) {
+  DEFINE_SELF(MessageBuilderContext, self, _self);
+  VALUE name, type, number, type_class;
+
+  if (argc < 3) {
+    rb_raise(rb_eArgError, "Expected at least 3 arguments.");
+  }
+  name = argv[0];
+  type = argv[1];
+  number = argv[2];
+  type_class = (argc > 3) ? argv[3] : Qnil;
+
+  return msgdef_add_field(self->descriptor, "required",
+                          name, type, number, type_class);
+}
+
+/*
+ * 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=).
+ */
+VALUE MessageBuilderContext_repeated(int argc, VALUE* argv, VALUE _self) {
+  DEFINE_SELF(MessageBuilderContext, self, _self);
+  VALUE name, type, number, type_class;
+
+  if (argc < 3) {
+    rb_raise(rb_eArgError, "Expected at least 3 arguments.");
+  }
+  name = argv[0];
+  type = argv[1];
+  number = argv[2];
+  type_class = (argc > 3) ? argv[3] : Qnil;
+
+  return msgdef_add_field(self->descriptor, "repeated",
+                          name, type, number, type_class);
+}
+
+/*
+ * 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=).
+ */
+VALUE MessageBuilderContext_map(int argc, VALUE* argv, VALUE _self) {
+  DEFINE_SELF(MessageBuilderContext, self, _self);
+  VALUE name, key_type, value_type, number, type_class;
+  VALUE mapentry_desc, mapentry_desc_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.");
+  }
+
+  // Create a new message descriptor for the map entry message, and create a
+  // repeated submessage field here with that type.
+  mapentry_desc = rb_class_new_instance(0, NULL, cDescriptor);
+  mapentry_desc_name = rb_funcall(self->descriptor, rb_intern("name"), 0);
+  mapentry_desc_name = rb_str_cat2(mapentry_desc_name, "_MapEntry_");
+  mapentry_desc_name = rb_str_cat2(mapentry_desc_name,
+                                   rb_id2name(SYM2ID(name)));
+  Descriptor_name_set(mapentry_desc, mapentry_desc_name);
+
+  {
+    // The 'mapentry' attribute has no Ruby setter because we do not want the
+    // user attempting to DIY the setup below; we want to ensure that the fields
+    // are correct. So we reach into the msgdef here to set the bit manually.
+    Descriptor* mapentry_desc_self = ruby_to_Descriptor(mapentry_desc);
+    upb_msgdef_setmapentry((upb_msgdef*)mapentry_desc_self->msgdef, true);
+  }
+
+  {
+    // optional <type> key = 1;
+    VALUE key_field = rb_class_new_instance(0, NULL, cFieldDescriptor);
+    FieldDescriptor_name_set(key_field, rb_str_new2("key"));
+    FieldDescriptor_label_set(key_field, ID2SYM(rb_intern("optional")));
+    FieldDescriptor_number_set(key_field, INT2NUM(1));
+    FieldDescriptor_type_set(key_field, key_type);
+    Descriptor_add_field(mapentry_desc, key_field);
+  }
+
+  {
+    // optional <type> value = 2;
+    VALUE value_field = rb_class_new_instance(0, NULL, cFieldDescriptor);
+    FieldDescriptor_name_set(value_field, rb_str_new2("value"));
+    FieldDescriptor_label_set(value_field, ID2SYM(rb_intern("optional")));
+    FieldDescriptor_number_set(value_field, INT2NUM(2));
+    FieldDescriptor_type_set(value_field, value_type);
+    if (type_class != Qnil) {
+      VALUE submsg_name = rb_str_new2("."); // prepend '.' to make absolute.
+      submsg_name = rb_str_append(submsg_name, type_class);
+      FieldDescriptor_submsg_name_set(value_field, submsg_name);
+    }
+    Descriptor_add_field(mapentry_desc, value_field);
+  }
+
+  {
+    // Add the map-entry message type to the current builder, and use the type
+    // to create the map field itself.
+    Builder* builder_self = ruby_to_Builder(self->builder);
+    rb_ary_push(builder_self->pending_list, mapentry_desc);
+  }
+
+  {
+    VALUE map_field = rb_class_new_instance(0, NULL, cFieldDescriptor);
+    VALUE name_str = rb_str_new2(rb_id2name(SYM2ID(name)));
+    VALUE submsg_name;
+
+    FieldDescriptor_name_set(map_field, name_str);
+    FieldDescriptor_number_set(map_field, number);
+    FieldDescriptor_label_set(map_field, ID2SYM(rb_intern("repeated")));
+    FieldDescriptor_type_set(map_field, ID2SYM(rb_intern("message")));
+    submsg_name = rb_str_new2("."); // prepend '.' to make name absolute.
+    submsg_name = rb_str_append(submsg_name, mapentry_desc_name);
+    FieldDescriptor_submsg_name_set(map_field, submsg_name);
+    Descriptor_add_field(self->descriptor, map_field);
+  }
+
+  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.
+ */
+VALUE MessageBuilderContext_oneof(VALUE _self, VALUE name) {
+  DEFINE_SELF(MessageBuilderContext, self, _self);
+  VALUE oneofdef = rb_class_new_instance(0, NULL, cOneofDescriptor);
+  VALUE args[2] = { oneofdef, self->builder };
+  VALUE ctx = rb_class_new_instance(2, args, cOneofBuilderContext);
+  VALUE block = rb_block_proc();
+  VALUE name_str = rb_str_new2(rb_id2name(SYM2ID(name)));
+  rb_funcall(oneofdef, rb_intern("name="), 1, name_str);
+  rb_funcall_with_block(ctx, rb_intern("instance_eval"), 0, NULL, block);
+  Descriptor_add_oneof(self->descriptor, oneofdef);
+
+  return Qnil;
+}
+
+// -----------------------------------------------------------------------------
+// OneofBuilderContext.
+// -----------------------------------------------------------------------------
+
+DEFINE_CLASS(OneofBuilderContext,
+    "Google::Protobuf::Internal::OneofBuilderContext");
+
+void OneofBuilderContext_mark(void* _self) {
+  OneofBuilderContext* self = _self;
+  rb_gc_mark(self->descriptor);
+  rb_gc_mark(self->builder);
+}
+
+void OneofBuilderContext_free(void* _self) {
+  OneofBuilderContext* self = _self;
+  xfree(self);
+}
+
+VALUE OneofBuilderContext_alloc(VALUE klass) {
+  OneofBuilderContext* self = ALLOC(OneofBuilderContext);
+  VALUE ret = TypedData_Wrap_Struct(
+      klass, &_OneofBuilderContext_type, self);
+  self->descriptor = Qnil;
+  self->builder = Qnil;
+  return ret;
+}
+
+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);
+  cOneofBuilderContext = klass;
+  rb_gc_register_address(&cOneofBuilderContext);
+}
+
+/*
+ * call-seq:
+ *     OneofBuilderContext.new(desc, 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.
+ */
+VALUE OneofBuilderContext_initialize(VALUE _self,
+                                     VALUE oneofdef,
+                                     VALUE builder) {
+  DEFINE_SELF(OneofBuilderContext, self, _self);
+  self->descriptor = oneofdef;
+  self->builder = builder;
+  return Qnil;
+}
+
+/*
+ * call-seq:
+ *     OneofBuilderContext.optional(name, type, number, type_class = 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=).
+ */
+VALUE OneofBuilderContext_optional(int argc, VALUE* argv, VALUE _self) {
+  DEFINE_SELF(OneofBuilderContext, self, _self);
+  VALUE name, type, number, type_class;
+
+  if (argc < 3) {
+    rb_raise(rb_eArgError, "Expected at least 3 arguments.");
+  }
+  name = argv[0];
+  type = argv[1];
+  number = argv[2];
+  type_class = (argc > 3) ? argv[3] : Qnil;
+
+  return msgdef_add_field(self->descriptor, "optional",
+                          name, type, number, type_class);
+}
+
+// -----------------------------------------------------------------------------
+// EnumBuilderContext.
+// -----------------------------------------------------------------------------
+
+DEFINE_CLASS(EnumBuilderContext,
+    "Google::Protobuf::Internal::EnumBuilderContext");
+
+void EnumBuilderContext_mark(void* _self) {
+  EnumBuilderContext* self = _self;
+  rb_gc_mark(self->enumdesc);
+}
+
+void EnumBuilderContext_free(void* _self) {
+  EnumBuilderContext* self = _self;
+  xfree(self);
+}
+
+VALUE EnumBuilderContext_alloc(VALUE klass) {
+  EnumBuilderContext* self = ALLOC(EnumBuilderContext);
+  VALUE ret = TypedData_Wrap_Struct(
+      klass, &_EnumBuilderContext_type, self);
+  self->enumdesc = Qnil;
+  return ret;
+}
+
+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, 1);
+  rb_define_method(klass, "value", EnumBuilderContext_value, 2);
+  cEnumBuilderContext = klass;
+  rb_gc_register_address(&cEnumBuilderContext);
+}
+
+/*
+ * call-seq:
+ *     EnumBuilderContext.new(enumdesc) => 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.
+ */
+VALUE EnumBuilderContext_initialize(VALUE _self, VALUE enumdef) {
+  DEFINE_SELF(EnumBuilderContext, self, _self);
+  self->enumdesc = enumdef;
+  return Qnil;
+}
+
+static VALUE enumdef_add_value(VALUE enumdef,
+                               VALUE name, VALUE number) {
+  rb_funcall(enumdef, rb_intern("add_value"), 2, name, number);
+  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.
+ */
+VALUE EnumBuilderContext_value(VALUE _self, VALUE name, VALUE number) {
+  DEFINE_SELF(EnumBuilderContext, self, _self);
+  return enumdef_add_value(self->enumdesc, name, number);
+}
+
+// -----------------------------------------------------------------------------
+// Builder.
+// -----------------------------------------------------------------------------
+
+DEFINE_CLASS(Builder, "Google::Protobuf::Internal::Builder");
+
+void Builder_mark(void* _self) {
+  Builder* self = _self;
+  rb_gc_mark(self->pending_list);
+}
+
+void Builder_free(void* _self) {
+  Builder* self = _self;
+  xfree(self->defs);
+  xfree(self);
+}
+
+/*
+ * call-seq:
+ *     Builder.new => 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.
+ */
+VALUE Builder_alloc(VALUE klass) {
+  Builder* self = ALLOC(Builder);
+  VALUE ret = TypedData_Wrap_Struct(
+      klass, &_Builder_type, self);
+  self->pending_list = rb_ary_new();
+  self->defs = NULL;
+  return ret;
+}
+
+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, "add_message", Builder_add_message, 1);
+  rb_define_method(klass, "add_enum", Builder_add_enum, 1);
+  rb_define_method(klass, "finalize_to_pool", Builder_finalize_to_pool, 1);
+  cBuilder = klass;
+  rb_gc_register_address(&cBuilder);
+}
+
+/*
+ * call-seq:
+ *     Builder.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.
+ */
+VALUE Builder_add_message(VALUE _self, VALUE name) {
+  DEFINE_SELF(Builder, self, _self);
+  VALUE msgdef = rb_class_new_instance(0, NULL, cDescriptor);
+  VALUE args[2] = { msgdef, _self };
+  VALUE ctx = rb_class_new_instance(2, args, cMessageBuilderContext);
+  VALUE block = rb_block_proc();
+  rb_funcall(msgdef, rb_intern("name="), 1, name);
+  rb_funcall_with_block(ctx, rb_intern("instance_eval"), 0, NULL, block);
+  rb_ary_push(self->pending_list, msgdef);
+  return Qnil;
+}
+
+/*
+ * call-seq:
+ *     Builder.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.
+ */
+VALUE Builder_add_enum(VALUE _self, VALUE name) {
+  DEFINE_SELF(Builder, self, _self);
+  VALUE enumdef = rb_class_new_instance(0, NULL, cEnumDescriptor);
+  VALUE ctx = rb_class_new_instance(1, &enumdef, cEnumBuilderContext);
+  VALUE block = rb_block_proc();
+  rb_funcall(enumdef, rb_intern("name="), 1, name);
+  rb_funcall_with_block(ctx, rb_intern("instance_eval"), 0, NULL, block);
+  rb_ary_push(self->pending_list, enumdef);
+  return Qnil;
+}
+
+static void validate_msgdef(const upb_msgdef* msgdef) {
+  // Verify that no required fields exist. proto3 does not support these.
+  upb_msg_field_iter it;
+  for (upb_msg_field_begin(&it, msgdef);
+       !upb_msg_field_done(&it);
+       upb_msg_field_next(&it)) {
+    const upb_fielddef* field = upb_msg_iter_field(&it);
+    if (upb_fielddef_label(field) == UPB_LABEL_REQUIRED) {
+      rb_raise(rb_eTypeError, "Required fields are unsupported in proto3.");
+    }
+  }
+}
+
+static void validate_enumdef(const upb_enumdef* enumdef) {
+  // Verify that an entry exists with integer value 0. (This is the default
+  // value.)
+  const char* lookup = upb_enumdef_iton(enumdef, 0);
+  if (lookup == NULL) {
+    rb_raise(rb_eTypeError,
+             "Enum definition does not contain a value for '0'.");
+  }
+}
+
+/*
+ * call-seq:
+ *     Builder.finalize_to_pool(pool)
+ *
+ * Adds all accumulated message and enum descriptors created in this builder
+ * context to the given pool. The operation occurs atomically, and all
+ * descriptors can refer to each other (including in cycles). This is the only
+ * way to build (co)recursive message definitions.
+ *
+ * This method is usually called automatically by DescriptorPool#build after it
+ * invokes the given user block in the context of the builder. The user should
+ * not normally need to call this manually because a Builder is not normally
+ * created manually.
+ */
+VALUE Builder_finalize_to_pool(VALUE _self, VALUE pool_rb) {
+  DEFINE_SELF(Builder, self, _self);
+
+  DescriptorPool* pool = ruby_to_DescriptorPool(pool_rb);
+
+  REALLOC_N(self->defs, upb_def*, RARRAY_LEN(self->pending_list));
+
+  for (int i = 0; i < RARRAY_LEN(self->pending_list); i++) {
+    VALUE def_rb = rb_ary_entry(self->pending_list, i);
+    if (CLASS_OF(def_rb) == cDescriptor) {
+      self->defs[i] = (upb_def*)ruby_to_Descriptor(def_rb)->msgdef;
+      validate_msgdef((const upb_msgdef*)self->defs[i]);
+    } else if (CLASS_OF(def_rb) == cEnumDescriptor) {
+      self->defs[i] = (upb_def*)ruby_to_EnumDescriptor(def_rb)->enumdef;
+      validate_enumdef((const upb_enumdef*)self->defs[i]);
+    }
+  }
+
+  CHECK_UPB(upb_symtab_add(pool->symtab, (upb_def**)self->defs,
+                           RARRAY_LEN(self->pending_list), NULL, &status),
+            "Unable to add defs to DescriptorPool");
+
+  for (int i = 0; i < RARRAY_LEN(self->pending_list); i++) {
+    VALUE def_rb = rb_ary_entry(self->pending_list, i);
+    add_def_obj(self->defs[i], def_rb);
+  }
+
+  self->pending_list = rb_ary_new();
+  return Qnil;
+}