ProtocolBuffers.ProtoParser.ParseField C# (CSharp) Method

        static bool ParseField(TokenReader tr, Message m)
        {
            string rule = tr.ReadNext ();
            while (true) {
                if (ParseComment (rule) == false)
                    break;
                rule = tr.ReadNext ();
            }

            if (rule == "}")
                return false;

            if (rule == "enum") {
                MessageEnum me = ParseEnum (tr, m);
                m.Enums.Add (me);
                return true;
            }

            Field f = new Field ();
            f.Comments = lastComment;
            lastComment = null;

            //Rule
            switch (rule) {
            case "required":
                f.Rule = FieldRule.Required;
                break;
            case "optional":
                f.Rule = FieldRule.Optional;
                break;
            case "repeated":
                f.Rule = FieldRule.Repeated;
                break;
            case "option":
                //Save options
                ParseOption (tr, m);
                return true;
            case "message":
                m.Messages.Add (ParseMessage (tr, m));
                return true;
            default:
                throw new ProtoFormatException ("unknown rule: " + rule);
            }

            //Type
            f.ProtoTypeName = tr.ReadNext ();

            //Name
            f.Name = tr.ReadNext ();

            //ID
            tr.ReadNextOrThrow ("=");
            f.ID = int.Parse (tr.ReadNext ());
            if (19000 <= f.ID && f.ID <= 19999)
                throw new ProtoFormatException ("Can't use reserved field ID 19000-19999");
            if (f.ID > (1 << 29) - 1)
                throw new ProtoFormatException ("Maximum field id is 2^29 - 1");

            //Add Field to message
            m.Fields.Add (f.ID, f);

            //Determine if extra options
            string extra = tr.ReadNext ();
            if (extra == ";")
                return true;

            //Field options
            if (extra != "[")
                throw new ProtoFormatException ("Expected: [ got " + extra);

            while (true) {
                string key = tr.ReadNext ();
                tr.ReadNextOrThrow ("=");
                string val = tr.ReadNext ();

                ParseFieldOption (key, val, f);
                string optionSep = tr.ReadNext ();
                if (optionSep == "]")
                    break;
                if (optionSep == ",")
                    continue;
                throw new ProtoFormatException (@"Expected "","" or ""]"" got " + tr.Next);
            }
            tr.ReadNextOrThrow (";");

            return true;
        }