Ticket #37347: 37347.diff

wp-admin/includes/class-wp-upgrader.php

@@ -808 +808 @@
        public function maintenance_mode( $enable = false ) {
                global $wp_filesystem;
                $file = $wp_filesystem->abspath() . '.maintenance';
+               /**
+                * Filters whether to enable maintenance mode
+                *
+                * @since 4.6
+                * @access public
+                *
+                * @param bool        $enable  Whether to apply maintenance mode
+                * @param WP_Upgrader $this    The WP_Upgrader instance.
+                */
+               $enable = apply_filters( 'maintenance_mode', $enable, $this );
                if ( $enable ) {
                        $this->skin->feedback('maintenance_start');
                        // Create maintenance file to signal that we are upgrading