Implement inline replies feature (#1408)

* Message#reply and replyFormat
* MessageAction#reference and referenceById
* MessageAction#mentionRepliedUser and setDefaultMentionRepliedUser isDefaultMentionRepliedUser
* New MessageType INLINE_REPLY
* Improve handling of mentions in messages

src/main/java/net/dv8tion/jda/api/entities/Message.java

@@ -23,6 +23,7 @@
 import net.dv8tion.jda.api.requests.restaction.AuditableRestAction;
 import net.dv8tion.jda.api.requests.restaction.MessageAction;
 import net.dv8tion.jda.api.requests.restaction.pagination.ReactionPaginationAction;
+import net.dv8tion.jda.api.utils.AttachmentOption;
 import net.dv8tion.jda.internal.JDAImpl;
 import net.dv8tion.jda.internal.requests.FunctionalCallback;
 import net.dv8tion.jda.internal.requests.Requester;
@@ -199,6 +200,18 @@ public interface Message extends ISnowflake, Formattable
             "(?:\\?\\S*)?(?:#\\S*)?",                                      // Useless query or URN appendix
             Pattern.CASE_INSENSITIVE);
 
+    /**
+     * Referenced message.
+     *
+     * <p>This will have different meaning depending on the {@link #getType() type} of message.
+     * Usually, this is a {@link MessageType#INLINE_REPLY INLINE_REPLY} reference.
+     * This can be null even if the type is {@link MessageType#INLINE_REPLY INLINE_REPLY}, when the message it references doesn't exist or discord wasn't able to resolve it in time.
+     *
+     * @return The referenced message, or null
+     */
+    @Nullable
+    Message getReferencedMessage();
+
     /**
      * An immutable list of all mentioned {@link net.dv8tion.jda.api.entities.User Users}.
      * <br>If no user was mentioned, this list is empty. Elements are sorted in order of appearance. This only
@@ -948,6 +961,174 @@ default boolean isFromGuild()
     @CheckReturnValue
     MessageAction editMessage(@Nonnull Message newContent);
 
+    /**
+     * Replies and references this message.
+     * <br>This is identical to {@code message.getChannel().sendMessage(content).reference(message)}.
+     * You can use {@link MessageAction#mentionRepliedUser(boolean) mentionRepliedUser(false)} to not mention the author of the message.
+     *
+     * <p>For further info, see {@link MessageChannel#sendMessage(CharSequence)} and {@link MessageAction#reference(Message)}.
+     *
+     * @param  content
+     *         The content of the reply message
+     *
+     * @return {@link MessageAction} Providing the {@link Message} created from this upload.
+     */
+    @Nonnull
+    @CheckReturnValue
+    default MessageAction reply(@Nonnull CharSequence content)
+    {
+        return getChannel().sendMessage(content).reference(this);
+    }
+
+    /**
+     * Replies and references this message.
+     * <br>This is identical to {@code message.getChannel().sendMessage(content).reference(message)}.
+     * You can use {@link MessageAction#mentionRepliedUser(boolean) mentionRepliedUser(false)} to not mention the author of the message.
+     *
+     * <p>For further info, see {@link MessageChannel#sendMessage(MessageEmbed)} and {@link MessageAction#reference(Message)}.
+     *
+     * @param  content
+     *         The content of the reply message
+     *
+     * @return {@link MessageAction} Providing the {@link Message} created from this upload.
+     */
+    @Nonnull
+    @CheckReturnValue
+    default MessageAction reply(@Nonnull MessageEmbed content)
+    {
+        return getChannel().sendMessage(content).reference(this);
+    }
+
+    /**
+     * Replies and references this message.
+     * <br>This is identical to {@code message.getChannel().sendMessage(content).reference(message)}.
+     * You can use {@link MessageAction#mentionRepliedUser(boolean) mentionRepliedUser(false)} to not mention the author of the message.
+     *
+     * <p>For further info, see {@link MessageChannel#sendMessage(Message)} and {@link MessageAction#reference(Message)}.
+     *
+     * @param  content
+     *         The content of the reply message
+     *
+     * @return {@link MessageAction} Providing the {@link Message} created from this upload.
+     */
+    @Nonnull
+    @CheckReturnValue
+    default MessageAction reply(@Nonnull Message content)
+    {
+        return getChannel().sendMessage(content).reference(this);
+    }
+
+    /**
+     * Replies and references this message.
+     * <br>This is identical to {@code message.getChannel().sendMessageFormat(content, args).reference(message)}.
+     * You can use {@link MessageAction#mentionRepliedUser(boolean) mentionRepliedUser(false)} to not mention the author of the message.
+     *
+     * <p>For further info, see {@link MessageChannel#sendMessageFormat(String, Object...)} and {@link MessageAction#reference(Message)}.
+     *
+     * @param  format
+     *         The string that should be formatted, if this is null or empty the content of the Message would be empty and cause a builder exception.
+     * @param  args
+     *         The arguments for your format
+     *
+     * @return {@link MessageAction} Providing the {@link Message} created from this upload.
+     */
+    @Nonnull
+    @CheckReturnValue
+    default MessageAction replyFormat(@Nonnull String format, @Nonnull Object... args)
+    {
+        return getChannel().sendMessageFormat(format, args).reference(this);
+    }
+
+    /**
+     * Replies and references this message.
+     * <br>This is identical to {@code message.getChannel().sendFile(file, options).reference(message)}.
+     * You can use {@link MessageAction#mentionRepliedUser(boolean) mentionRepliedUser(false)} to not mention the author of the message.
+     *
+     * <p>For further info, see {@link MessageChannel#sendFile(File, net.dv8tion.jda.api.utils.AttachmentOption...)} and {@link MessageAction#reference(Message)}.
+     *
+     * @param  file
+     *         The file to upload to the channel in the reply
+     * @param  options
+     *         Possible options to apply to this attachment, such as marking it as spoiler image
+     *
+     * @return {@link MessageAction} Providing the {@link Message} created from this upload.
+     */
+    @Nonnull
+    @CheckReturnValue
+    default MessageAction reply(@Nonnull File file, @Nonnull AttachmentOption... options)
+    {
+        return getChannel().sendFile(file, options).reference(this);
+    }
+
+    /**
+     * Replies and references this message.
+     * <br>This is identical to {@code message.getChannel().sendFile(data, name, options).reference(message)}.
+     * You can use {@link MessageAction#mentionRepliedUser(boolean) mentionRepliedUser(false)} to not mention the author of the message.
+     *
+     * <p>For further info, see {@link MessageChannel#sendFile(File, String, net.dv8tion.jda.api.utils.AttachmentOption...)} and {@link MessageAction#reference(Message)}.
+     *
+     * @param  data
+     *         The data to upload to the channel in the reply
+     * @param  name
+     *         The name that should be sent to discord
+     * @param  options
+     *         Possible options to apply to this attachment, such as marking it as spoiler image
+     *
+     * @return {@link MessageAction} Providing the {@link Message} created from this upload.
+     */
+    @Nonnull
+    @CheckReturnValue
+    default MessageAction reply(@Nonnull File data, @Nonnull String name, @Nonnull AttachmentOption... options)
+    {
+        return getChannel().sendFile(data, name, options).reference(this);
+    }
+
+    /**
+     * Replies and references this message.
+     * <br>This is identical to {@code message.getChannel().sendFile(data, name, options).reference(message)}.
+     * You can use {@link MessageAction#mentionRepliedUser(boolean) mentionRepliedUser(false)} to not mention the author of the message.
+     *
+     * <p>For further info, see {@link MessageChannel#sendFile(InputStream, String, net.dv8tion.jda.api.utils.AttachmentOption...)} and {@link MessageAction#reference(Message)}.
+     *
+     * @param  data
+     *         The data to upload to the channel in the reply
+     * @param  name
+     *         The name that should be sent to discord
+     * @param  options
+     *         Possible options to apply to this attachment, such as marking it as spoiler image
+     *
+     * @return {@link MessageAction} Providing the {@link Message} created from this upload.
+     */
+    @Nonnull
+    @CheckReturnValue
+    default MessageAction reply(@Nonnull InputStream data, @Nonnull String name, @Nonnull AttachmentOption... options)
+    {
+        return getChannel().sendFile(data, name, options).reference(this);
+    }
+
+    /**
+     * Replies and references this message.
+     * <br>This is identical to {@code message.getChannel().sendFile(data, name, options).reference(message)}.
+     * You can use {@link MessageAction#mentionRepliedUser(boolean) mentionRepliedUser(false)} to not mention the author of the message.
+     *
+     * <p>For further info, see {@link MessageChannel#sendFile(byte[], String, net.dv8tion.jda.api.utils.AttachmentOption...)} and {@link MessageAction#reference(Message)}.
+     *
+     * @param  data
+     *         The data to upload to the channel in the reply
+     * @param  name
+     *         The name that should be sent to discord
+     * @param  options
+     *         Possible options to apply to this attachment, such as marking it as spoiler image
+     *
+     * @return {@link MessageAction} Providing the {@link Message} created from this upload.
+     */
+    @Nonnull
+    @CheckReturnValue
+    default MessageAction reply(@Nonnull byte[] data, @Nonnull String name, @Nonnull AttachmentOption... options)
+    {
+        return getChannel().sendFile(data, name, options).reference(this);
+    }
+
     /**
      * Deletes this Message from Discord.
      * <br>If this Message was not sent by the currently logged in account, then this will fail unless the Message is from

src/main/java/net/dv8tion/jda/api/entities/MessageType.java

@@ -88,6 +88,11 @@ public enum MessageType
      */
     CHANNEL_FOLLOW_ADD(12),
 
+    /**
+     * Reply to another message. This usually comes with a {@link Message#getReferencedMessage() referenced message}.
+     */
+    INLINE_REPLY(19),
+
     /**
      * Unknown MessageType.
      */

src/main/java/net/dv8tion/jda/api/requests/restaction/MessageAction.java

@@ -16,12 +16,14 @@
 
 package net.dv8tion.jda.api.requests.restaction;
 
+import net.dv8tion.jda.api.MessageBuilder;
 import net.dv8tion.jda.api.entities.IMentionable;
 import net.dv8tion.jda.api.entities.Message;
 import net.dv8tion.jda.api.entities.MessageChannel;
 import net.dv8tion.jda.api.entities.MessageEmbed;
 import net.dv8tion.jda.api.requests.RestAction;
 import net.dv8tion.jda.api.utils.AttachmentOption;
+import net.dv8tion.jda.api.utils.MiscUtil;
 import net.dv8tion.jda.internal.requests.restaction.MessageActionImpl;
 import net.dv8tion.jda.internal.utils.Checks;
 
@@ -123,6 +125,33 @@ static EnumSet<Message.MentionType> getDefaultMentions()
         return MessageActionImpl.getDefaultMentions();
     }
 
+    /**
+     * Sets the default value for {@link #mentionRepliedUser(boolean)}
+     *
+     * <p>Default: <b>true</b>
+     *
+     * @param mention
+     *        True, if replies should mention by default
+     */
+    static void setDefaultMentionRepliedUser(boolean mention)
+    {
+        MessageActionImpl.setDefaultMentionRepliedUser(mention);
+    }
+
+    /**
+     * Returns the default mention behavior for replies.
+     * <br>If this is {@code true} then all replies will mention the author of the target message by default.
+     * You can specify this individually with {@link #mentionRepliedUser(boolean)} for each message.
+     *
+     * <p>Default: <b>true</b>
+     *
+     * @return True, if replies mention by default
+     */
+    static boolean isDefaultMentionRepliedUser()
+    {
+        return MessageActionImpl.isDefaultMentionRepliedUser();
+    }
+
     @Nonnull
     @Override
     MessageAction setCheck(@Nullable BooleanSupplier checks);
@@ -181,6 +210,85 @@ static EnumSet<Message.MentionType> getDefaultMentions()
     @CheckReturnValue
     MessageAction apply(@Nullable final Message message);
 
+    /**
+     * Make the message a reply to the referenced message.
+     * <br>You can only reply to messages from the same channel!
+     * <br>This will mention the author of the target message. You can disable this through {@link #mentionRepliedUser(boolean)}.
+     *
+     * <p>This requires {@link net.dv8tion.jda.api.Permission#MESSAGE_HISTORY Permission.MESSAGE_HISTORY} in the channel!
+     *
+     * @param  messageId
+     *         The target message
+     *
+     * @return Updated MessageAction for chaining convenience
+     */
+    @Nonnull
+    @CheckReturnValue
+    MessageAction referenceById(long messageId);
+
+    /**
+     * Make the message a reply to the referenced message.
+     * <br>You can only reply to messages from the same channel!
+     * <br>This will mention the author of the target message. You can disable this through {@link #mentionRepliedUser(boolean)}.
+     *
+     * <p>This requires {@link net.dv8tion.jda.api.Permission#MESSAGE_HISTORY Permission.MESSAGE_HISTORY} in the channel!
+     * You cannot reply to system messages (such as {@link net.dv8tion.jda.api.entities.MessageType#CHANNEL_PINNED_ADD CHANNEL_PINNED_ADD} and similar).
+     *
+     * @param  messageId
+     *         The target message
+     *
+     * @throws IllegalArgumentException
+     *         If the provided ID is null or not a valid snowflake
+     *
+     * @return Updated MessageAction for chaining convenience
+     */
+    @Nonnull
+    @CheckReturnValue
+    default MessageAction referenceById(@Nonnull String messageId)
+    {
+        return referenceById(MiscUtil.parseSnowflake(messageId));
+    }
+
+    /**
+     * Make the message a reply to the referenced message.
+     * <br>You can only reply to messages from the same channel!
+     * <br>This will mention the author of the target message. You can disable this through {@link #mentionRepliedUser(boolean)}.
+     *
+     * <p>This requires {@link net.dv8tion.jda.api.Permission#MESSAGE_HISTORY Permission.MESSAGE_HISTORY} in the channel!
+     *
+     * @param  message
+     *         The target message
+     *
+     * @throws IllegalArgumentException
+     *         If the provided message is null
+     * @throws UnsupportedOperationException
+     *         If the provided message is from a {@link MessageBuilder}
+     *
+     * @return Updated MessageAction for chaining convenience
+     */
+    @Nonnull
+    @CheckReturnValue
+    default MessageAction reference(@Nonnull Message message)
+    {
+        Checks.notNull(message, "Message");
+        return referenceById(message.getIdLong());
+    }
+
+    /**
+     * Whether to mention the used, when replying to a message.
+     * <br>This only matters in combination with {@link #reference(Message)} and {@link #referenceById(long)}!
+     *
+     * <p>This is true by default but can be configured using {@link #setDefaultMentionRepliedUser(boolean)}!
+     *
+     * @param  mention
+     *         True, to mention the author if the referenced message
+     *
+     * @return Updated MessageAction for chaining convenience
+     */
+    @Nonnull
+    @CheckReturnValue
+    MessageAction mentionRepliedUser(boolean mention);
+
     /**
      * Enable/Disable Text-To-Speech for the resulting message.
      * <br>This is only relevant to MessageActions that are not {@code isEdit() == true}!

src/main/java/net/dv8tion/jda/internal/entities/AbstractMessage.java

@@ -106,6 +106,12 @@ protected void appendFormat(Formatter formatter, int width, int precision, boole
         }
     }
 
+    @Override
+    public Message getReferencedMessage()
+    {
+        return null;
+    }
+
     @Nonnull
     @Override
     public Bag<User> getMentionedUsersBag()