Don't allow two same accounts being logged in.

Telegram/SourceFiles/intro/intro_phone.cpp

@@ -16,7 +16,10 @@ https://github.com/telegramdesktop/tdesktop/blob/master/LEGAL
 #include "ui/wrap/fade_wrap.h"
 #include "ui/special_fields.h"
 #include "main/main_account.h"
+#include "main/main_domain.h"
 #include "main/main_app_config.h"
+#include "main/main_session.h"
+#include "data/data_user.h"
 #include "boxes/confirm_phone_box.h"
 #include "boxes/confirm_box.h"
 #include "core/application.h"
@@ -138,6 +141,24 @@ void PhoneWidget::submit() {
 		return;
 	}
 
+	// Check if such account is authorized already.
+	const auto digitsOnly = [](QString value) {
+		return value.replace(QRegularExpression("[^0-9]"), QString());
+	};
+	const auto phoneDigits = digitsOnly(phone);
+	for (const auto &[index, existing] : Core::App().domain().accounts()) {
+		const auto raw = existing.get();
+		if (const auto session = raw->maybeSession()) {
+			if (raw->mtp().environment() == account().mtp().environment()
+				&& digitsOnly(session->user()->phone()) == phoneDigits) {
+				crl::on_main(raw, [=] {
+					Core::App().domain().activate(raw);
+				});
+				return;
+			}
+		}
+	}
+
 	hidePhoneError();
 
 	_checkRequestTimer.callEach(1000);

Telegram/SourceFiles/intro/intro_step.cpp

@@ -13,6 +13,7 @@ https://github.com/telegramdesktop/tdesktop/blob/master/LEGAL
 #include "lang/lang_keys.h"
 #include "lang/lang_cloud_manager.h"
 #include "main/main_account.h"
+#include "main/main_domain.h"
 #include "main/main_session.h"
 #include "main/main_session_settings.h"
 #include "core/application.h"
@@ -144,6 +145,21 @@ void Step::finish(const MTPUser &user, QImage &&photo) {
 		return;
 	}
 
+	// Check if such account is authorized already.
+	for (const auto &[index, existing] : Core::App().domain().accounts()) {
+		const auto raw = existing.get();
+		if (const auto session = raw->maybeSession()) {
+			if (raw->mtp().environment() == _account->mtp().environment()
+				&& user.c_user().vid().v == session->userId()) {
+				_account->logOut();
+				crl::on_main(raw, [=] {
+					Core::App().domain().activate(raw);
+				});
+				return;
+			}
+		}
+	}
+
 	// Save the default language if we've suggested some other and user ignored it.
 	const auto currentId = Lang::Current().id();
 	const auto defaultId = Lang::DefaultLanguageId();
@@ -152,7 +168,6 @@ void Step::finish(const MTPUser &user, QImage &&photo) {
 		Lang::Current().switchToId(Lang::DefaultLanguage());
 		Local::writeLangPack();
 	}
-
 	const auto account = _account;
 	account->createSession(user);
 

Telegram/SourceFiles/main/main_account.cpp

@@ -126,8 +126,13 @@ void Account::watchSessionChanges() {
 	}, _lifetime);
 }
 
-UserId Account::willHaveUserId() const {
+uint64 Account::willHaveSessionUniqueId(MTP::Config *config) const {
-	return _sessionUserId;
+	// See also Session::uniqueId.
+	if (!_sessionUserId) {
+		return 0;
+	}
+	return uint64(uint32(_sessionUserId))
+		| (config && config->isTestMode() ? 0x0100'0000'0000'0000ULL : 0ULL);
 }
 
 void Account::createSession(const MTPUser &user) {

Telegram/SourceFiles/main/main_account.h

@@ -48,7 +48,7 @@ public:
 		std::shared_ptr<MTP::AuthKey> localKey);
 	void start(std::unique_ptr<MTP::Config> config);
 
-	[[nodiscard]] UserId willHaveUserId() const;
+	[[nodiscard]] uint64 willHaveSessionUniqueId(MTP::Config *config) const;
 	void createSession(const MTPUser &user);
 	void createSession(
 		UserId id,

Telegram/SourceFiles/main/main_session.cpp

@@ -166,11 +166,9 @@ base::Observable<void> &Session::downloaderTaskFinished() {
 }
 
 uint64 Session::uniqueId() const {
-	auto result = uint64(uint32(userId()));
+	// See also Account::willHaveSessionUniqueId.
-	if (mtp().isTestMode()) {
+	return uint64(uint32(userId()))
-		result |= 0x0100'0000'0000'0000ULL;
+		| (mtp().isTestMode() ? 0x0100'0000'0000'0000ULL : 0ULL);
-	}
-	return result;
 }
 
 UserId Session::userId() const {

Telegram/SourceFiles/storage/storage_domain.cpp

@@ -169,7 +169,7 @@ Domain::StartModernResult Domain::startModern(
 	_oldVersion = keyData.version;
 
 	auto tried = base::flat_set<int>();
-	auto users = base::flat_set<UserId>();
+	auto sessions = base::flat_set<uint64>();
 	auto active = 0;
 	for (auto i = 0; i != count; ++i) {
 		auto index = qint32();
@@ -182,10 +182,11 @@ Domain::StartModernResult Domain::startModern(
 				_dataName,
 				index);
 			auto config = account->prepareToStart(_localKey);
-			const auto userId = account->willHaveUserId();
+			const auto sessionId = account->willHaveSessionUniqueId(
-			if (!users.contains(userId)
+				config.get());
-				&& (userId != 0 || (users.empty() && i + 1 == count))) {
+			if (!sessions.contains(sessionId)
-				if (users.empty()) {
+				&& (sessionId != 0 || (sessions.empty() && i + 1 == count))) {
+				if (sessions.empty()) {
 					active = index;
 				}
 				account->start(std::move(config));
@@ -193,16 +194,21 @@ Domain::StartModernResult Domain::startModern(
 					.index = index,
 					.account = std::move(account)
 				});
-				users.emplace(userId);
+				sessions.emplace(sessionId);
 			}
 		}
 	}
+	if (sessions.empty()) {
+		LOG(("App Error: no accounts read."));
+		return StartModernResult::Failed;
+	}
+
 	if (!info.stream.atEnd()) {
 		info.stream >> active;
 	}
 	_owner->activateFromStorage(active);
 
-	Ensures(!users.empty());
+	Ensures(!sessions.empty());
 	return StartModernResult::Success;
 }