Don't push sublists to stack endlessly.

Telegram/SourceFiles/mainwidget.cpp

@@ -1379,7 +1379,7 @@ void MainWidget::showHistory(
 
 	if (!back && (way != Way::ClearStack)) {
 		// This may modify the current section, for example remove its contents.
-		saveSectionInStack();
+		saveSectionInStack(params);
 	}
 
 	if (_history->peer()
@@ -1501,13 +1501,23 @@ Ui::ChatTheme *MainWidget::customChatTheme() const {
 	return _history->customChatTheme();
 }
 
-void MainWidget::saveSectionInStack() {
+bool MainWidget::saveSectionInStack(
+		const SectionShow &params,
+		Window::SectionWidget *newMainSection) {
 	if (_mainSection) {
 		if (auto memento = _mainSection->createMemento()) {
+			if (params.dropSameFromStack
+				&& newMainSection
+				&& newMainSection->sameTypeAs(memento.get())) {
+				// When choosing saved sublist we want to save the original
+				// "Saved Messages" in the stack, but don't save every
+				// sublist in a new stack entry when clicking them through.
+				return false;
+			}
 			_stack.push_back(std::make_unique<StackItemSection>(
 				std::move(memento)));
 		} else {
-			return;
+			return false;
 		}
 	} else if (const auto history = _history->history()) {
 		_stack.push_back(std::make_unique<StackItemHistory>(
@@ -1515,7 +1525,7 @@ void MainWidget::saveSectionInStack() {
 			_history->msgId(),
 			_history->replyReturns()));
 	} else {
-		return;
+		return false;
 	}
 	const auto raw = _stack.back().get();
 	raw->setThirdSectionWeak(_thirdSection.data());
@@ -1528,6 +1538,7 @@ void MainWidget::saveSectionInStack() {
 			}
 		}
 	}, raw->lifetime());
+	return true;
 }
 
 void MainWidget::showSection(
@@ -1730,7 +1741,11 @@ void MainWidget::showNewSection(
 
 	if (saveInStack) {
 		// This may modify the current section, for example remove its contents.
-		saveSectionInStack();
+		if (!saveSectionInStack(params, newMainSection)) {
+			saveInStack = false;
+			animatedShow = false;
+			animationParams = Window::SectionSlideParams();
+		}
 	}
 	auto &settingSection = newThirdSection
 		? _thirdSection