MDL-21912 restore: Add admin setting to restore conflicting admin user

admin/settings/courses.php

@@ -205,6 +205,9 @@
     // Create a page for general import configuration and defaults.
     $temp = new admin_settingpage('importgeneralsettings', new lang_string('importgeneralsettings', 'backup'), 'moodle/backup:backupcourse');
     $temp->add(new admin_setting_configtext('backup/import_general_maxresults', new lang_string('importgeneralmaxresults', 'backup'), new lang_string('importgeneralmaxresults_desc', 'backup'), 10));
+    $temp->add(new admin_setting_configcheckbox('backup/import_general_duplicate_admin_allowed',
+            new lang_string('importgeneralduplicateadminallowed', 'backup'),
+            new lang_string('importgeneralduplicateadminallowed_desc', 'backup'), 0));
     $ADMIN->add('backups', $temp);
 
     // Create a page for automated backups configuration and defaults.

backup/util/dbops/restore_dbops.class.php

@@ -1287,7 +1287,11 @@ public static function create_included_users($basepath, $restoreid, $userid,
     *      1F - None of the above, return true => User needs to be created
     *
     *  if restoring from another site backup (cannot match by id here, replace it by email/firstaccess combination):
-    *      2A - Normal check: If match by username and mnethost and (email or non-zero firstaccess) => ok, return target user
+    *      2A - Normal check:
+    *           2A1 - If match by username and mnethost and (email or non-zero firstaccess) => ok, return target user
+    *           2A2 - Exceptional handling (MDL-21912): Match "admin" username. Then, if import_general_duplicate_admin_allowed is
+    *                 enabled, attempt to map the admin user to the user 'admin_[oldsiteid]' if it exists. If not,
+    *                 the user 'admin_[oldsiteid]' will be created in precheck_included users
     *      2B - Handle users deleted in DB and "alive" in backup file:
     *           2B1 - If match by mnethost and user is deleted in DB and not empty email = md5(username) and
     *                 (username LIKE 'backup_email.%' or non-zero firstaccess) => ok, return target user
@@ -1305,7 +1309,7 @@ public static function create_included_users($basepath, $restoreid, $userid,
     * Note: for DB deleted users md5(username) is stored *sometimes* in the email field,
     *       hence we are looking there for usernames if not empty. See delete_user()
     */
-    protected static function precheck_user($user, $samesite) {
+    protected static function precheck_user($user, $samesite, $siteid = null) {
         global $CFG, $DB;
 
         // Handle checks from same site backups
@@ -1376,7 +1380,7 @@ protected static function precheck_user($user, $samesite) {
         // Handle checks from different site backups
         } else {
 
-            // 2A - If match by username and mnethost and
+            // 2A1 - If match by username and mnethost and
             //     (email or non-zero firstaccess) => ok, return target user
             if ($rec = $DB->get_record_sql("SELECT *
                                               FROM {user} u
@@ -1393,6 +1397,14 @@ protected static function precheck_user($user, $samesite) {
                 return $rec; // Matching user found, return it
             }
 
+            // 2A2 - If we're allowing conflicting admins, attempt to map user to admin_[oldsiteid].
+            if (get_config('backup', 'import_general_duplicate_admin_allowed') && $user->username === 'admin' && $siteid
+                    && $user->mnethostid == $CFG->mnet_localhost_id) {
+                if ($rec = $DB->get_record('user', array('username' => 'admin_' . $siteid))) {
+                    return $rec;
+                }
+            }
+
             // 2B - Handle users deleted in DB and "alive" in backup file
             // Note: for DB deleted users email is stored in username field, hence we
             //       are looking there for emails. See delete_user()
@@ -1500,6 +1512,9 @@ public static function precheck_included_users($restoreid, $courseid, $userid, $
         // Calculate the context we are going to use for capability checking
         $context = context_course::instance($courseid);
 
+        // When conflicting users are detected we may need original site info.
+        $restoreinfo = restore_controller_dbops::load_controller($restoreid)->get_info();
+
         // Calculate if we have perms to create users, by checking:
         // to 'moodle/restore:createuser' and 'moodle/restore:userinfo'
         // and also observe $CFG->disableusercreationonrestore
@@ -1535,14 +1550,28 @@ public static function precheck_included_users($restoreid, $courseid, $userid, $
             }
 
             // Now, precheck that user and, based on returned results, annotate action/problem
-            $usercheck = self::precheck_user($user, $samesite);
+            $usercheck = self::precheck_user($user, $samesite, $restoreinfo->original_site_identifier_hash);
 
             if (is_object($usercheck)) { // No problem, we have found one user in DB to be mapped to
                 // Annotate it, for later process. Set newitemid to mapping user->id
                 self::set_backup_ids_record($restoreid, 'user', $recuser->itemid, $usercheck->id);
 
             } else if ($usercheck === false) { // Found conflict, report it as problem
-                 $problems[] = get_string('restoreuserconflict', '', $user->username);
+                if (!get_config('backup', 'import_general_duplicate_admin_allowed')) {
+                    $problems[] = get_string('restoreuserconflict', '', $user->username);
+                } else if ($user->username == 'admin') {
+                    if (!$cancreateuser) {
+                        $problems[] = get_string('restorecannotcreateuser', '', $user->username);
+                    }
+                    if ($user->mnethostid != $CFG->mnet_localhost_id) {
+                        $problems[] = get_string('restoremnethostidmismatch', '', $user->username);
+                    }
+                    if (!$problems) {
+                        // Duplicate admin allowed, append original site idenfitier to username.
+                        $user->username .= '_' . $restoreinfo->original_site_identifier_hash;
+                        self::set_backup_ids_record($restoreid, 'user', $recuser->itemid, 0, null, (array)$user);
+                    }
+                }
 
             } else if ($usercheck === true) { // User needs to be created, check if we are able
                 if ($cancreateuser) { // Can create user, set newitemid to 0 so will be created later

lang/en/backup.php

@@ -148,6 +148,8 @@
 $string['importgeneralsettings'] = 'General import defaults';
 $string['importgeneralmaxresults'] = 'Maximum number of courses listed for import';
 $string['importgeneralmaxresults_desc'] = 'This controls the number of courses that are listed during the first step of the import process';
+$string['importgeneralduplicateadminallowed'] = 'Allow admin conflict resolution';
+$string['importgeneralduplicateadminallowed_desc'] = 'If the site has an account with username \'admin\', then attempting to restore a backup file containing an account with username \'admin\' can cause a conflict. If this setting is enabled, the conflict will be resolved by changing the username in the backup file to \'admin_xyz\'.';
 $string['importfile'] = 'Import a backup file';
 $string['importbackupstage1action'] = 'Next';
 $string['importbackupstage2action'] = 'Next';

lang/en/moodle.php

@@ -1551,6 +1551,7 @@
 $string['restorecannotassignroles'] = 'Restore needs to assign roles and you do not have permission to do so';
 $string['restorecannotcreateorassignroles'] = 'Restore needs to create or assign roles and you do not have permission to do so';
 $string['restorecannotcreateuser'] = 'Restore needs to create user \'{$a}\' from backup file and you do not have permission to do so';
+$string['restoremnethostidmismatch'] = 'MNet host id of user \'{$a}\' does not match local MNet host ID.';
 $string['restorecannotoverrideperms'] = 'Restore needs to override permissions and you do not have permission to do so';
 $string['restorecoursenow'] = 'Restore this course now!';
 $string['restoredaccount'] = 'Restored account';