ChatComponent.java

	private void addMessage(Component message, @Nullable MessageSignature signature, int ticks, @Nullable GuiMessageTag tag, boolean refresh) {
		int i = Mth.floor((double)this.getWidth() / this.getScale());
		if (tag != null && tag.icon() != null) {
			i -= tag.icon().width + 4 + 2;
		}

		List<FormattedCharSequence> list = ComponentRenderUtils.wrapComponents(message, i, this.minecraft.font);
		boolean bl = this.isChatFocused();

		for(int j = 0; j < list.size(); ++j) {
			FormattedCharSequence formattedCharSequence = (FormattedCharSequence)list.get(j);
			if (bl && this.chatScrollbarPos > 0) {
				this.newMessageSinceScroll = true;
				this.scrollChat(1);
			}

			boolean bl2 = j == list.size() - 1;
			this.trimmedMessages.add(0, new GuiMessage.Line(ticks, formattedCharSequence, tag, bl2));
		}

		while(this.trimmedMessages.size() > 100) {
			this.trimmedMessages.remove(this.trimmedMessages.size() - 1);
		}

		if (!refresh) {
			this.allMessages.add(0, new GuiMessage(ticks, message, signature, tag));

			while(this.allMessages.size() > 100) {
				this.allMessages.remove(this.allMessages.size() - 1);
			}
		}
	}

ChatComponentMixin.java

    @ModifyExpressionValue(method = "addMessage(Lnet/minecraft/network/chat/Component;Lnet/minecraft/network/chat/MessageSignature;ILnet/minecraft/client/GuiMessageTag;Z)V", at = @At(value = "NEW", target = "Lnet/minecraft/client/GuiMessage$Line;<init>(ILnet/minecraft/util/FormattedCharSequence;Lnet/minecraft/client/GuiMessageTag;Z)V"))
    private GuiMessage.Line hookMessageLineAdd(GuiMessage.Line line, @Share("lines") LocalRef<List<GuiMessage.Line>> linesRef) {
        if (linesRef.get() == null)
            linesRef.set(new ArrayList<>());
        linesRef.get().add(line);
        return line;
    }

    @ModifyExpressionValue(method = "addMessage(Lnet/minecraft/network/chat/Component;Lnet/minecraft/network/chat/MessageSignature;ILnet/minecraft/client/GuiMessageTag;Z)V", at = @At(value = "NEW", target = "Lnet/minecraft/client/GuiMessage;<init>(ILnet/minecraft/network/chat/Component;Lnet/minecraft/network/chat/MessageSignature;Lnet/minecraft/client/GuiMessageTag;)V"))
    private GuiMessage hookMessageAdd(GuiMessage message, @Share("lines") LocalRef<List<GuiMessage.Line>> linesRef) {
        messageToLines.put(message, linesRef.get());
        return message;
    }