From 3b1d13eac91e1f46aa0e29f916f1a8ff447b435b Mon Sep 17 00:00:00 2001
From: John Preston <johnprestonmail@gmail.com>
Date: Fri, 17 Mar 2023 17:51:53 +0400
Subject: [PATCH] Clear memory while scrolling in topics / discussions.

---
 .../history/view/history_view_list_widget.cpp | 25 ++++++++++++++++---
 .../history/view/history_view_list_widget.h   | 12 +++++----
 2 files changed, 28 insertions(+), 9 deletions(-)

diff --git a/Telegram/SourceFiles/history/view/history_view_list_widget.cpp b/Telegram/SourceFiles/history/view/history_view_list_widget.cpp
index 85347cb76..639c35ce5 100644
--- a/Telegram/SourceFiles/history/view/history_view_list_widget.cpp
+++ b/Telegram/SourceFiles/history/view/history_view_list_widget.cpp
@@ -490,6 +490,8 @@ void ListWidget::setGeometryCrashAnnotations(not_null<Element*> view) {
 }
 
 void ListWidget::refreshRows(const Data::MessagesSlice &old) {
+	Expects(_viewsCapacity.empty());
+
 	saveScrollState();
 
 	const auto addedToEndFrom = (old.skippedAfter == 0
@@ -507,13 +509,14 @@ void ListWidget::refreshRows(const Data::MessagesSlice &old) {
 	_resizePending = true;
 	_items.clear();
 	_items.reserve(_slice.ids.size());
+	std::swap(_views, _viewsCapacity);
 	auto nearestIndex = -1;
 	for (const auto &fullId : _slice.ids) {
 		if (const auto item = session().data().message(fullId)) {
 			if (_slice.nearestToAround == fullId) {
 				nearestIndex = int(_items.size());
 			}
-			const auto view = enforceViewForItem(item);
+			const auto view = enforceViewForItem(item, _viewsCapacity);
 			_items.push_back(view);
 			if (destroyingBarElement == view) {
 				destroyingBarElement = nullptr;
@@ -541,6 +544,13 @@ void ListWidget::refreshRows(const Data::MessagesSlice &old) {
 		_bar = {};
 	}
 
+	for (const auto &[item, view] : _viewsCapacity) {
+		if (const auto raw = view.get()) {
+			viewReplaced(raw, nullptr);
+		}
+	}
+	_viewsCapacity.clear();
+
 	checkUnreadBarCreation();
 	restoreScrollState();
 	if (!_itemsRevealHeight) {
@@ -868,9 +878,16 @@ Element *ListWidget::viewForItem(const HistoryItem *item) const {
 }
 
 not_null<Element*> ListWidget::enforceViewForItem(
-		not_null<HistoryItem*> item) {
-	if (const auto view = viewForItem(item)) {
-		return view;
+		not_null<HistoryItem*> item,
+		ViewsMap &old) {
+	if (const auto i = old.find(item); i != end(old)) {
+		if (i->second) {
+			return _views.emplace(
+				item,
+				base::take(i->second)).first->second.get();
+		} else if (const auto j = _views.find(item); j != end(_views)) {
+			return j->second.get();
+		}
 	}
 	const auto [i, ok] = _views.emplace(
 		item,
diff --git a/Telegram/SourceFiles/history/view/history_view_list_widget.h b/Telegram/SourceFiles/history/view/history_view_list_widget.h
index c8ad5f1fc..ad3517723 100644
--- a/Telegram/SourceFiles/history/view/history_view_list_widget.h
+++ b/Telegram/SourceFiles/history/view/history_view_list_widget.h
@@ -359,6 +359,9 @@ private:
 	using PointState = HistoryView::PointState;
 	using CursorState = HistoryView::CursorState;
 	using ChosenReaction = HistoryView::Reactions::ChosenReaction;
+	using ViewsMap = base::flat_map<
+		not_null<HistoryItem*>,
+		std::unique_ptr<Element>>;
 
 	struct MouseState {
 		MouseState();
@@ -433,7 +436,9 @@ private:
 
 	Element *viewForItem(FullMsgId itemId) const;
 	Element *viewForItem(const HistoryItem *item) const;
-	not_null<Element*> enforceViewForItem(not_null<HistoryItem*> item);
+	not_null<Element*> enforceViewForItem(
+		not_null<HistoryItem*> item,
+		ViewsMap &old);
 
 	void mouseActionStart(
 		const QPoint &globalPosition,
@@ -623,10 +628,7 @@ private:
 	int _idsLimit = kMinimalIdsLimit;
 	Data::MessagesSlice _slice;
 	std::vector<not_null<Element*>> _items;
-	std::map<
-		not_null<HistoryItem*>,
-		std::unique_ptr<Element>,
-		std::less<>> _views;
+	ViewsMap _views, _viewsCapacity;
 	int _itemsTop = 0;
 	int _itemsWidth = 0;
 	int _itemsHeight = 0;