introduce new virtual method hasUserListings() to determine if a user backend can list it's users.

apps/user_ldap/user_ldap.php

@@ -261,4 +261,10 @@ class USER_LDAP extends lib\Access implements \OCP\UserInterface {
 		return (bool)((OC_USER_BACKEND_CHECK_PASSWORD | OC_USER_BACKEND_GET_HOME) & $actions);
 	}
 
+	/**
+	 * @return bool
+	 */
+	public function hasUserListings() {
+		return true;
+	}
 }

apps/user_ldap/user_proxy.php

@@ -183,4 +183,12 @@ class User_Proxy extends lib\Proxy implements \OCP\UserInterface {
 	public function deleteUser($uid) {
 		return false;
 	}
+
+	/**
+	 * @return bool
+	 */
+	public function hasUserListings() {
+		return true;
+	}
+
 }

apps/user_webdavauth/user_webdavauth.php

@@ -65,6 +65,12 @@ class OC_USER_WEBDAVAUTH extends OC_User_Backend {
 		return true;
 	}
 
+	/**
+	 * @return bool
+	 */
+	public function hasUserListings() {
+		return false;
+	}
 
 	/*
 	* we don´t know the users so all we can do it return an empty array here

lib/user.php

@@ -555,7 +555,7 @@ class OC_User {
 
     public static function userExistsForCreation($uid) {
         foreach(self::$_usedBackends as $backend) {
-            if(!$backend->implementsActions(OC_USER_BACKEND_CREATE_USER))
+            if(!$backend->hasUserListings())
                 continue;
 
             $result=$backend->userExists($uid);

lib/user/backend.php

@@ -136,7 +136,7 @@ abstract class OC_User_Backend implements OC_User_Interface {
 	
 	/**
 	 * @brief Get a list of all display names
-	 * @returns array with  all displayNames (value) and the correspondig uids (key)
+	 * @returns array with  all displayNames (value) and the corresponding uids (key)
 	 *
 	 * Get a list of all display names and user ids.
 	 */
@@ -148,4 +148,12 @@ abstract class OC_User_Backend implements OC_User_Interface {
 		}
 		return $displayNames;
 	}
+
+	/**
+	 * @brief Check if a user list is available or not
+	 * @return boolean if users can be listed or not
+	 */
+	public function hasUserListings() {
+		return false;
+	}
 }

lib/user/database.php

@@ -256,4 +256,12 @@ class OC_User_Database extends OC_User_Backend {
 			return false;
 		}
 	}
+
+	/**
+	 * @return bool
+	 */
+	public function hasUserListings() {
+		return true;
+	}
+
 }

lib/user/dummy.php

@@ -112,4 +112,11 @@ class OC_User_Dummy extends OC_User_Backend {
 	public function userExists($uid) {
 		return isset($this->users[$uid]);
 	}
+
+	/**
+	 * @return bool
+	 */
+	public function hasUserListings() {
+		return true;
+	}
 }

lib/user/interface.php

@@ -66,10 +66,15 @@ interface OC_User_Interface {
 
 	/**
 	 * @brief Get a list of all display names
-	 * @returns array with  all displayNames (value) and the correspondig uids (key)
+	 * @returns array with  all displayNames (value) and the corresponding uids (key)
 	 *
 	 * Get a list of all display names and user ids.
 	 */
 	public function getDisplayNames($search = '', $limit = null, $offset = null);
 
+	/**
+	 * @brief Check if a user list is available or not
+	 * @return boolean if users can be listed or not
+	 */
+	public function hasUserListings();
 }