Add abstract bakend to still be backwards compatible with the old logic

Signed-off-by: Roeland Jago Douma <roeland@famdouma.nl>

lib/public/User/Backend/AbstractBackend.php

@@ -0,0 +1,62 @@
+<?php
+declare(strict_types=1);
+/**
+* @copyright Copyright (c) 2018 Roeland Jago Douma <roeland@famdouma.nl>
+*
+* @author Roeland Jago Douma <roeland@famdouma.nl>
+*
+* @license GNU AGPL version 3 or any later version
+*
+* This program is free software: you can redistribute it and/or modify
+* it under the terms of the GNU Affero General Public License as
+* published by the Free Software Foundation, either version 3 of the
+* License, or (at your option) any later version.
+*
+* This program is distributed in the hope that it will be useful,
+* but WITHOUT ANY WARRANTY; without even the implied warranty of
+* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+* GNU Affero General Public License for more details.
+*
+* You should have received a copy of the GNU Affero General Public License
+* along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*
+*/
+
+namespace OCP\User\Backend;
+
+use OC\User\Backend;
+use OCP\IUserBackend;
+use OCP\UserInterface;
+
+abstract class AbstractBackend implements IUserBackend, UserInterface {
+	public function implementsActions($actions): bool {
+		$implements = 0;
+
+		if ($this instanceof ICreateUserBackend) {
+			$implements |= Backend::CREATE_USER;
+		}
+		if ($this instanceof ISetPasswordBackend) {
+			$implements |= Backend::SET_PASSWORD;
+		}
+		if ($this instanceof ICheckPasswordBackend) {
+			$implements |= Backend::CHECK_PASSWORD;
+		}
+		if ($this instanceof IGetHomeBackend) {
+			$implements |= Backend::GET_HOME;
+		}
+		if ($this instanceof IGetDisplayNameBackend) {
+			$implements |= Backend::GET_DISPLAYNAME;
+		}
+		if ($this instanceof ISetDisplayNameBackend) {
+			$implements |= Backend::SET_DISPLAYNAME;
+		}
+		if ($this instanceof IProvideAvatarBackend) {
+			$implements |= Backend::PROVIDE_AVATAR;
+		}
+		if ($this instanceof ICountUsersBackend) {
+			$implements |= Backend::COUNT_USERS;
+		}
+
+		return (bool)($actions & $implements);
+	}
+}