Widget preview not working if widget registered via a instance

[spacedmonkey]

While testing the current WordPress 5.8 beta 2, I found an issue with widget preview.

The register_widget function can be called with a class name or a class instance. Once called with a class instance, the class instance is converted to hash as used key in array. See widget factory

         public function register( $widget ) {
                if ( $widget instanceof WP_Widget ) {
                        $this->widgets[ spl_object_hash( $widget ) ] = $widget;
                } else {
                        $this->widgets[ $widget ] = new $widget();
                }
        }

In the new widget type controller, this method only passed by class name.

        private function get_widget_preview( $widget_object, $instance ) {
                ob_start();
                the_widget( get_class( $widget_object ), $instance );
                return ob_get_clean();
        }

In the_widget function, there is no look for spl_object_hash.

if ( ! isset( $wp_widget_factory->widgets[ $widget ] ) ) {
                _doing_it_wrong(
                        __FUNCTION__,
                        sprintf(
                                /* translators: %s: register_widget() */
                                __( 'Widgets need to be registered using %s, before they can be displayed.' ),
                                '<code>register_widget()</code>'
                        ),
                        '4.9.0'
                );
                return;
        }

        $widget_obj = $wp_widget_factory->widgets[ $widget ];
        if ( ! ( $widget_obj instanceof WP_Widget ) ) {
                return;
        }

Trac ticket: https://core.trac.wordpress.org/ticket/53427

[spacedmonkey]

For more context, see #28216

Trac ticket: https://core.trac.wordpress.org/ticket/53427

[noisysocks]

Looks good @spacedmonkey!

src/wp-includes/blocks/legacy-widget.php (and all block PHP) is copied from @wordpress/widgets during grunt build --dev so we'll have to make those changes upstream in the Gutenberg repo instead:

​https://github.com/WordPress/gutenberg/blob/trunk/packages/widgets/src/blocks/legacy-widget/index.php

[spacedmonkey]

@noisysocks I have created a PR on the gutenberg repo - ​https://github.com/WordPress/gutenberg/pull/32781

[noisysocks]

Awesome. Let's wait until GB32781 is merged and back ported to Core and then we can commit everything except the src/wp-includes/blocks/legacy-widget.php changes that are in ​https://github.com/WordPress/wordpress-develop/pull/1378.

[spacedmonkey]

Now that GB32781 is merged, should should be good merge this. We will have to update the widget package at the same time.

Not sure how this affects #53441

[zieladam]

I wanted to test this but I don't have any function-based widgets installed. Would you share the one you use for testing?

[spacedmonkey]

@zieladam This patch doesn't fix function based widgets. It fixes an issue when if you pass an WP_Widget instance to register_widget it would not work.

I found this via a plugin I worked on called ​web-stories. See how we ​register our widget.

If you install our plugin, 1.8.0 or high you can help test.

[noisysocks]

r51216 fixes this.

fixed in https://core.trac.wordpress.org/changeset/51216.

[desrosj]

#53481 was marked as a duplicate.