[Feature] add Thread property to RestMessage (#2575)

src/Discord.Net.Rest/API/Common/Message.cs

@@ -64,5 +64,8 @@ namespace Discord.API
         public Optional<StickerItem[]> StickerItems { get; set; }
         [JsonProperty("role_subscription_data")]
         public Optional<MessageRoleSubscriptionData> RoleSubscriptionData { get; set; }
+
+        [JsonProperty("thread")]
+        public Optional<Channel> Thread { get; set; }
     }
 }

src/Discord.Net.Rest/Entities/Messages/RestMessage.cs

@@ -80,10 +80,19 @@ namespace Discord.Rest
         /// <inheritdoc/>
         public MessageType Type { get; private set; }
 
+
+        /// <summary>
+        ///     Gets the thread that was started from this message.
+        /// </summary>
+        /// <returns>
+        ///    A <see cref="RestThreadChannel"/> object if this message has thread attached; otherwise <see langword="null"/>.
+        /// </returns>
+        public RestThreadChannel Thread { get; private set; }
+
         /// <inheritdoc />
         public MessageRoleSubscriptionData RoleSubscriptionData { get; private set; }
 
-        /// <inheritdoc/>
+        /// <inheritdoc cref="IMessage.Components"/>
         public IReadOnlyCollection<ActionRowComponent> Components { get; private set; }
         /// <summary>
         ///     Gets a collection of the mentioned users in the message.
@@ -255,6 +264,11 @@ namespace Discord.Rest
                     model.RoleSubscriptionData.Value.MonthsSubscribed,
                     model.RoleSubscriptionData.Value.IsRenewal);
             }
+
+            if (model.Thread.IsSpecified)
+            {
+                Thread = RestThreadChannel.Create(Discord, new RestGuild(Discord, model.Thread.Value.GuildId.Value), model.Thread.Value);
+            }
         }
         /// <inheritdoc />
         public async Task UpdateAsync(RequestOptions options = null)
@@ -274,11 +288,17 @@ namespace Discord.Rest
         /// </returns>
         public override string ToString() => Content;
 
+        #region IMessage
+
+        /// <inheritdoc />
         IUser IMessage.Author => Author;
+
         /// <inheritdoc />
         IReadOnlyCollection<IAttachment> IMessage.Attachments => Attachments;
+
         /// <inheritdoc />
         IReadOnlyCollection<IEmbed> IMessage.Embeds => Embeds;
+
         /// <inheritdoc />
         IReadOnlyCollection<ulong> IMessage.MentionedUserIds => MentionedUsers.Select(x => x.Id).ToImmutableArray();
 
@@ -291,6 +311,8 @@ namespace Discord.Rest
         /// <inheritdoc />
         IReadOnlyCollection<IStickerItem> IMessage.Stickers => Stickers;
         
+        #endregion
+
         /// <inheritdoc />
         public IReadOnlyDictionary<IEmote, ReactionMetadata> Reactions => _reactions.ToDictionary(x => x.Emote, x => new ReactionMetadata { ReactionCount = x.Count, IsMe = x.Me });