Improve opening history with one loaded message.

When we add just one last item, like we do while loading dialogs,
we want to remove a single added grouped media, otherwise it will
jump once we open the message history (first we show only that
media, then we load the rest of the group and show the group).

That way when we open the message history we show nothing until a
whole history part is loaded, it certainly will contain the group.

Telegram/SourceFiles/history/history.cpp

@@ -1114,11 +1114,15 @@ not_null<HistoryItem*> History::addNewService(MsgId msgId, QDateTime date, const
 }
 
 HistoryItem *History::addNewMessage(const MTPMessage &msg, NewMessageType type) {
-	if (isChannel()) return asChannelHistory()->addNewChannelMessage(msg, type);
+	if (isChannel()) {
+		return asChannelHistory()->addNewChannelMessage(msg, type);
+	}
 
-	if (type == NewMessageExisting) return addToHistory(msg);
+	if (type == NewMessageExisting) {
+		return addToHistory(msg);
+	}
 	if (!loadedAtBottom() || peer->migrateTo()) {
-		HistoryItem *item = addToHistory(msg);
+		const auto item = addToHistory(msg);
 		if (item) {
 			setLastMessage(item);
 			if (type == NewMessageUnread) {
@@ -1132,13 +1136,24 @@ HistoryItem *History::addNewMessage(const MTPMessage &msg, NewMessageType type)
 }
 
 HistoryItem *History::addNewToLastBlock(const MTPMessage &msg, NewMessageType type) {
-	auto applyServiceAction = (type == NewMessageUnread);
+	const auto applyServiceAction = (type == NewMessageUnread);
-	auto detachExistingItem = (type != NewMessageLast);
+	const auto detachExistingItem = (type != NewMessageLast);
-	auto item = createItem(msg, applyServiceAction, detachExistingItem);
+	const auto item = createItem(msg, applyServiceAction, detachExistingItem);
 	if (!item || !item->detached()) {
 		return item;
 	}
-	return addNewItem(item, (type == NewMessageUnread));
+	const auto result = addNewItem(item, (type == NewMessageUnread));
+	if (type == NewMessageLast) {
+		// When we add just one last item, like we do while loading dialogs,
+		// we want to remove a single added grouped media, otherwise it will
+		// jump once we open the message history (first we show only that
+		// media, then we load the rest of the group and show the group).
+		//
+		// That way when we open the message history we show nothing until a
+		// whole history part is loaded, it certainly will contain the group.
+		removeOrphanMediaGroupPart();
+	}
+	return result;
 }
 
 HistoryItem *History::addToHistory(const MTPMessage &msg) {
@@ -1251,6 +1266,7 @@ void History::addUnreadMentionsSlice(const MTPmessages_Messages &result) {
 
 not_null<HistoryItem*> History::addNewItem(not_null<HistoryItem*> adding, bool newMsg) {
 	Expects(!isBuildingFrontBlock());
+
 	addItemToBlock(adding);
 
 	const auto [groupFrom, groupTill] = recountGroupingFromTill(adding);
@@ -2417,6 +2433,25 @@ bool History::isDisplayedEmpty() const {
 	return isEmpty() || ((blocks.size() == 1) && blocks.front()->items.size() == 1 && blocks.front()->items.front()->isEmpty());
 }
 
+bool History::hasOrphanMediaGroupPart() const {
+	if (loadedAtTop() || !loadedAtBottom()) {
+		return false;
+	} else if (blocks.size() != 1) {
+		return false;
+	} else if (blocks.front()->items.size() != 1) {
+		return false;
+	}
+	return blocks.front()->items.front()->groupId() != MessageGroupId();
+}
+
+bool History::removeOrphanMediaGroupPart() {
+	if (hasOrphanMediaGroupPart()) {
+		clear(true);
+		return true;
+	}
+	return false;
+}
+
 void History::clear(bool leaveItems) {
 	if (unreadBar) {
 		unreadBar = nullptr;

Telegram/SourceFiles/history/history.h

@@ -210,6 +210,8 @@ public:
 		return blocks.empty();
 	}
 	bool isDisplayedEmpty() const;
+	bool hasOrphanMediaGroupPart() const;
+	bool removeOrphanMediaGroupPart();
 
 	void clear(bool leaveItems = false);
 	void clearUpTill(MsgId availableMinId);