Added support of flexible scrollbar to Info::ContentWidget.

Telegram/SourceFiles/info/info_content_widget.cpp

@@ -225,6 +225,10 @@ int ContentWidget::scrollTopSave() const {
 	return _scroll->scrollTop();
 }
 
+rpl::producer<int> ContentWidget::scrollTopValue() const {
+	return _scroll->scrollTopValue();
+}
+
 void ContentWidget::scrollTopRestore(int scrollTop) {
 	_scroll->scrollToY(scrollTop);
 }

Telegram/SourceFiles/info/info_content_widget.h

@@ -101,6 +101,7 @@ protected:
 	int scrollTopSave() const;
 	void scrollTopRestore(int scrollTop);
 	void scrollTo(const Ui::ScrollToRequest &request);
+	[[nodiscard]] rpl::producer<int> scrollTopValue() const;
 
 private:
 	RpWidget *doSetInnerWidget(object_ptr<RpWidget> inner);

Telegram/SourceFiles/info/settings/info_settings_widget.cpp

@@ -44,9 +44,34 @@ Widget::Widget(
 : ContentWidget(parent, controller)
 , _self(controller->key().settingsSelf())
 , _type(controller->section().settingsType())
-, _inner(
-	setInnerWidget(
-		_type()->create(this, controller->parentController())))
+, _inner([&] {
+	auto inner = _type()->create(this, controller->parentController());
+	if (inner->hasFlexibleTopBar()) {
+		auto filler = setInnerWidget(object_ptr<Ui::RpWidget>(this));
+		filler->resize(1, 1);
+
+		_flexibleScroll.contentHeightValue.events(
+		) | rpl::start_with_next([=](int h) {
+			filler->resize(filler->width(), h);
+		}, filler->lifetime());
+
+		filler->widthValue(
+		) | rpl::start_to_stream(
+			_flexibleScroll.fillerWidthValue,
+			lifetime());
+
+		// ScrollArea -> PaddingWrap -> RpWidget.
+		inner->setParent(filler->parentWidget()->parentWidget());
+		inner->raise();
+
+		using InnerPtr = base::unique_qptr<::Settings::AbstractSection>;
+		auto owner = filler->lifetime().make_state<InnerPtr>(
+			std::move(inner.release()));
+		return owner->get();
+	} else {
+		return setInnerWidget(std::move(inner));
+	}
+}())
 , _pinnedToTop(_inner->createPinnedToTop(this))
 , _pinnedToBottom(_inner->createPinnedToBottom(this)) {
 	_inner->sectionShowOther(
@@ -103,6 +128,39 @@ Widget::Widget(
 			heightValue()
 		) | rpl::start_with_next(processHeight, _pinnedToBottom->lifetime());
 	}
+
+	if (_pinnedToTop
+		&& _pinnedToTop->minimumHeight()
+		&& _inner->hasFlexibleTopBar()) {
+		const auto heightDiff = [=] {
+			return _pinnedToTop->maximumHeight()
+				- _pinnedToTop->minimumHeight();
+		};
+
+		_inner->heightValue(
+		) | rpl::start_with_next([=](int h) {
+			_flexibleScroll.contentHeightValue.fire(h + heightDiff());
+		}, _pinnedToTop->lifetime());
+
+		scrollTopValue(
+		) | rpl::start_with_next([=](int top) {
+			if (!_pinnedToTop) {
+				return;
+			}
+			const auto current = heightDiff() - top;
+			_inner->moveToLeft(0, std::min(0, current));
+			_pinnedToTop->resize(
+				_pinnedToTop->width(),
+				std::max(current + _pinnedToTop->minimumHeight(), 0));
+		}, _inner->lifetime());
+
+		_flexibleScroll.fillerWidthValue.events(
+		) | rpl::start_with_next([=](int w) {
+			_inner->resizeToWidth(w);
+		}, _inner->lifetime());
+
+		setPaintPadding({ 0, _pinnedToTop->minimumHeight(), 0, 0 });
+	}
 }
 
 Widget::~Widget() = default;

Telegram/SourceFiles/info/settings/info_settings_widget.h

@@ -81,6 +81,10 @@ private:
 	not_null<UserData*> _self;
 	Type _type = Type();
 
+	struct {
+		rpl::event_stream<int> contentHeightValue;
+		rpl::event_stream<int> fillerWidthValue;
+	} _flexibleScroll;
 	not_null<::Settings::AbstractSection*> _inner;
 	QPointer<Ui::RpWidget> _pinnedToTop;
 	QPointer<Ui::RpWidget> _pinnedToBottom;

Telegram/SourceFiles/settings/settings_common.h

@@ -101,6 +101,9 @@ public:
 			not_null<Ui::RpWidget*> parent) {
 		return nullptr;
 	}
+	[[nodiscard]] virtual bool hasFlexibleTopBar() const {
+		return false;
+	}
 	virtual void setStepDataReference(std::any &data) {
 	}
 };

Telegram/SourceFiles/settings/settings_premium.cpp

@@ -44,6 +44,8 @@ public:
 	[[nodiscard]] QPointer<Ui::RpWidget> createPinnedToBottom(
 		not_null<Ui::RpWidget*> parent) override;
 
+	[[nodiscard]] bool hasFlexibleTopBar() const override;
+
 private:
 	void setupContent();
 
@@ -63,6 +65,10 @@ rpl::producer<QString> Premium::title() {
 	return tr::lng_premium_summary_title();
 }
 
+bool Premium::hasFlexibleTopBar() const {
+	return true;
+}
+
 void Premium::setupContent() {
 	const auto content = Ui::CreateChild<Ui::VerticalLayout>(this);