WP_REST_Widgets_Controller::update_item() WordPress Method

	public function update_item( $request ) {
		global $wp_widget_factory;

		/*
		 * retrieve_widgets() contains logic to move "hidden" or "lost" widgets to the
		 * wp_inactive_widgets sidebar based on the contents of the $sidebars_widgets global.
		 *
		 * When batch requests are processed, this global is not properly updated by previous
		 * calls, resulting in widgets incorrectly being moved to the wp_inactive_widgets
		 * sidebar.
		 *
		 * See https://core.trac.wordpress.org/ticket/53657.
		 */
		wp_get_sidebars_widgets();
		$this->retrieve_widgets();

		$widget_id  = $request['id'];
		$sidebar_id = wp_find_widgets_sidebar( $widget_id );

		// Allow sidebar to be unset or missing when widget is not a WP_Widget.
		$parsed_id     = wp_parse_widget_id( $widget_id );
		$widget_object = $wp_widget_factory->get_widget_object( $parsed_id['id_base'] );
		if ( is_null( $sidebar_id ) && $widget_object ) {
			return new WP_Error(
				'rest_widget_not_found',
				__( 'No widget was found with that id.' ),
				array( 'status' => 404 )
			);
		}

		if (
			$request->has_param( 'instance' ) ||
			$request->has_param( 'form_data' )
		) {
			$maybe_error = $this->save_widget( $request, $sidebar_id );
			if ( is_wp_error( $maybe_error ) ) {
				return $maybe_error;
			}
		}

		if ( $request->has_param( 'sidebar' ) ) {
			if ( $sidebar_id !== $request['sidebar'] ) {
				$sidebar_id = $request['sidebar'];
				wp_assign_widget_to_sidebar( $widget_id, $sidebar_id );
			}
		}

		$request['context'] = 'edit';

		return $this->prepare_item_for_response( compact( 'widget_id', 'sidebar_id' ), $request );
	}