WP_REST_Users_Controller::update_item PHP Method

    public function update_item($request)
    {
        $id = (int) $request['id'];
        $user = get_userdata($id);
        if (!$user) {
            return new WP_Error('rest_user_invalid_id', __('Invalid user ID.'), array('status' => 404));
        }
        if (email_exists($request['email']) && $request['email'] !== $user->user_email) {
            return new WP_Error('rest_user_invalid_email', __('Invalid email address.'), array('status' => 400));
        }
        if (!empty($request['username']) && $request['username'] !== $user->user_login) {
            return new WP_Error('rest_user_invalid_argument', __("Username isn't editable."), array('status' => 400));
        }
        if (!empty($request['slug']) && $request['slug'] !== $user->user_nicename && get_user_by('slug', $request['slug'])) {
            return new WP_Error('rest_user_invalid_slug', __('Invalid slug.'), array('status' => 400));
        }
        if (!empty($request['roles'])) {
            $check_permission = $this->check_role_update($id, $request['roles']);
            if (is_wp_error($check_permission)) {
                return $check_permission;
            }
        }
        $user = $this->prepare_item_for_database($request);
        // Ensure we're operating on the same user we already checked.
        $user->ID = $id;
        $user_id = wp_update_user(wp_slash((array) $user));
        if (is_wp_error($user_id)) {
            return $user_id;
        }
        $user = get_user_by('id', $user_id);
        /* This action is documented in lib/endpoints/class-wp-rest-users-controller.php */
        do_action('rest_insert_user', $user, $request, false);
        if (is_multisite() && !is_user_member_of_blog($id)) {
            add_user_to_blog(get_current_blog_id(), $id, '');
        }
        if (!empty($request['roles'])) {
            array_map(array($user, 'add_role'), $request['roles']);
        }
        $schema = $this->get_item_schema();
        if (!empty($schema['properties']['meta']) && isset($request['meta'])) {
            $meta_update = $this->meta->update_value($request['meta'], $id);
            if (is_wp_error($meta_update)) {
                return $meta_update;
            }
        }
        $user = get_user_by('id', $user_id);
        $fields_update = $this->update_additional_fields_for_object($user, $request);
        if (is_wp_error($fields_update)) {
            return $fields_update;
        }
        $request->set_param('context', 'edit');
        $response = $this->prepare_item_for_response($user, $request);
        $response = rest_ensure_response($response);
        return $response;
    }