Support empty group placeholder for creators.

Telegram/Resources/langs/lang.strings

@@ -1045,6 +1045,13 @@ https://github.com/telegramdesktop/tdesktop/blob/master/LEGAL
 "lng_group_stickers_description" = "You can choose a sticker set which will be available for every member while in the group chat.";
 "lng_group_stickers_add" = "Choose sticker set";
 
+"lng_group_about_header" = "You have created a group.";
+"lng_group_about_text" = "Groups can have:";
+"lng_group_about1" = "Up to 100,000 members";
+"lng_group_about2" = "Persistent chat history";
+"lng_group_about3" = "Public links such as t.me/title";
+"lng_group_about4" = "Admins with different rights";
+
 "lng_switch_stickers" = "Stickers";
 "lng_switch_emoji" = "Emoji";
 "lng_switch_gifs" = "GIFs";

Telegram/SourceFiles/boxes/peers/add_participants_box.h

@@ -24,8 +24,6 @@ public:
 		not_null<PeerData*> peer,
 		base::flat_set<not_null<UserData*>> &&alreadyIn);
 
-	using ContactsBoxController::ContactsBoxController;
-
 	void rowClicked(not_null<PeerListRow*> row) override;
 	void itemDeselectedHook(not_null<PeerData*> peer) override;
 

Telegram/SourceFiles/boxes/peers/edit_participants_box.h

@@ -14,8 +14,6 @@ https://github.com/telegramdesktop/tdesktop/blob/master/LEGAL
 #include "base/weak_ptr.h"
 #include "info/profile/info_profile_members_controllers.h"
 
-struct MegagroupInfo;
-
 namespace Window {
 class Navigation;
 } // namespace Window

Telegram/SourceFiles/history/history.cpp

@@ -2727,7 +2727,19 @@ bool History::isEmpty() const {
 }
 
 bool History::isDisplayedEmpty() const {
-	return findFirstNonEmpty() == nullptr;
+	const auto first = findFirstNonEmpty();
+	if (!first) {
+		return true;
+	} else if (!first->data()->isGroupEssential()) {
+		return false;
+	} else if (const auto chat = peer->asChat()) {
+		// For legacy chats we want to show the chat with only first
+		// message about you creating the group as an empty chat with
+		// a nice information about the group features.
+		return chat->amCreator() && (findLastNonEmpty() == first);
+	} else {
+		return false;
+	}
 }
 
 auto History::findFirstNonEmpty() const -> Element* {

Telegram/SourceFiles/history/history.style

@@ -543,3 +543,10 @@ boxAttachEmoji: IconButton(historyAttachEmoji) {
 	rippleAreaSize: 0px;
 }
 boxAttachEmojiTop: 20px;
+
+historyGroupAboutMargin: 16px;
+historyGroupAboutPadding: margins(24px, 16px, 24px, 16px);
+historyGroupAboutBulletSkip: 16px;
+historyGroupAboutHeaderSkip: 10px;
+historyGroupAboutTextSkip: 10px;
+historyGroupAboutSkip: 8px;

Telegram/SourceFiles/history/history_inner_widget.cpp

@@ -551,8 +551,8 @@ void HistoryInner::paintEvent(QPaintEvent *e) {
 
 			p.restoreTextPalette();
 		}
-	} else if (noHistoryDisplayed) {
+	} else if (historyDisplayedEmpty) {
-		HistoryView::paintEmpty(p, width(), height());
+		HistoryView::paintEmpty(p, _history, width(), height());
 	}
 	if (!noHistoryDisplayed) {
 		auto readMentions = base::flat_set<not_null<HistoryItem*>>();

Telegram/SourceFiles/history/history_widget.cpp

@@ -6555,9 +6555,9 @@ void HistoryWidget::paintEvent(QPaintEvent *e) {
 		if (_pinnedBar && !_pinnedBar->cancel->isHidden()) {
 			drawPinnedBar(p);
 		}
-		if (_scroll->isHidden()) {
+		if (_scroll->isHidden() && _history) {
 			p.setClipRect(_scroll->geometry());
-			HistoryView::paintEmpty(p, width(), height() - _field->height() - 2 * st::historySendPadding);
+			HistoryView::paintEmpty(p, _history, width(), height() - _field->height() - 2 * st::historySendPadding);
 		}
 	} else {
 		const auto w = st::msgServiceFont->width(lang(lng_willbe_history))

Telegram/SourceFiles/history/view/history_view_service_message.cpp

@@ -13,6 +13,8 @@ https://github.com/telegramdesktop/tdesktop/blob/master/LEGAL
 #include "history/history_item_components.h"
 #include "history/view/history_view_cursor_state.h"
 #include "data/data_abstract_structure.h"
+#include "data/data_chat.h"
+#include "data/data_channel.h"
 #include "styles/style_history.h"
 #include "mainwidget.h"
 #include "layout.h"
@@ -173,6 +175,83 @@ void paintPreparedDate(Painter &p, const QString &dateText, int dateTextWidth, i
 	p.drawText(left + st::msgServicePadding.left(), y + st::msgServiceMargin.top() + st::msgServicePadding.top() + st::msgServiceFont->ascent, dateText);
 }
 
+void PaintAboutGroup(Painter &p, int width, int height) {
+	constexpr auto kPhrasesCount = 4;
+	const auto header = lang(lng_group_about_header);
+	const auto text = lang(lng_group_about_text);
+	const auto phrases = std::array<QString, kPhrasesCount>{
+		lang(lng_group_about1),
+		lang(lng_group_about2),
+		lang(lng_group_about3),
+		lang(lng_group_about4),
+	};
+
+	const auto &font = st::msgServiceFont;
+	const auto headerWidth = font->width(header);
+	const auto textWidth = font->width(text);
+	const auto phraseWidths = ranges::view::all(
+		phrases
+	) | ranges::view::transform([&](const QString &text) {
+		return font->width(text);
+	}) | ranges::to_vector;
+
+	const auto maxPhraseWidth = *ranges::max_element(phraseWidths);
+
+	const auto margin = st::msgMargin.left();
+	const auto maxBubbleWidth = width - 2 * st::historyGroupAboutMargin;
+	const auto padding = st::historyGroupAboutPadding;
+	const auto bubbleWidth = std::min(
+		maxBubbleWidth,
+		std::max({
+			maxPhraseWidth + st::historyGroupAboutBulletSkip,
+			headerWidth,
+			textWidth }) + padding.left() + padding.right());
+	const auto bubbleHeight = padding.top()
+		+ font->height
+		+ st::historyGroupAboutHeaderSkip
+		+ font->height
+		+ st::historyGroupAboutTextSkip
+		+ font->height * kPhrasesCount
+		+ st::historyGroupAboutSkip * (kPhrasesCount - 1)
+		+ padding.bottom();
+	const auto bubbleLeft = (width - bubbleWidth) / 2;
+	const auto bubbleTop = (height - bubbleHeight) / 3;
+
+	ServiceMessagePainter::paintBubble(
+		p,
+		bubbleLeft,
+		bubbleTop,
+		bubbleWidth,
+		bubbleHeight);
+
+	p.setFont(font);
+	p.setPen(st::msgServiceFg);
+	const auto left = bubbleLeft + padding.left();
+	auto top = bubbleTop + padding.top();
+
+	p.drawTextLeft(bubbleLeft + (bubbleWidth - headerWidth) / 2, top, width, header);
+	top += font->height + st::historyGroupAboutHeaderSkip;
+
+	p.drawTextLeft(left, top, width, text);
+	top += font->height + st::historyGroupAboutTextSkip;
+
+	p.setBrush(st::msgServiceFg);
+	for (const auto &text : phrases) {
+		p.setPen(st::msgServiceFg);
+		p.drawTextLeft(left + st::historyGroupAboutBulletSkip, top, width, text);
+		{
+			PainterHighQualityEnabler hq(p);
+			p.setPen(Qt::NoPen);
+			p.drawEllipse(
+				left,
+				top + (font->height - st::mediaUnreadSize) / 2,
+				st::mediaUnreadSize,
+				st::mediaUnreadSize);
+		}
+		top += font->height + st::historyGroupAboutSkip;
+	}
+}
+
 } // namepsace
 
 int WideChatWidth() {
@@ -281,7 +360,22 @@ QVector<int> ServiceMessagePainter::countLineWidths(const Text &text, const QRec
 	return lineWidths;
 }
 
-void paintEmpty(Painter &p, int width, int height) {
+void paintEmpty(
+		Painter &p,
+		not_null<History*> history,
+		int width,
+		int height) {
+	const auto needAboutGroup = [&] {
+		if (const auto chat = history->peer->asChat()) {
+			return chat->amCreator();
+		} else if (const auto channel = history->peer->asMegagroup()) {
+			return channel->amCreator();
+		}
+		return false;
+	}();
+	if (needAboutGroup) {
+		PaintAboutGroup(p, width, height);
+	}
 }
 
 void serviceColorsUpdated() {

Telegram/SourceFiles/history/view/history_view_service_message.h

@@ -74,7 +74,11 @@ private:
 
 };
 
-void paintEmpty(Painter &p, int width, int height);
+void paintEmpty(
+	Painter &p,
+	not_null<History*> history,
+	int width,
+	int height);
 
 void serviceColorsUpdated();