"Pages in This Section" Block

add_action( 'init', function () {
    wp_register_script( 'wpide-block-sibling-pages', false, array( 'wp-blocks', 'wp-element', 'wp-block-editor', 'wp-server-side-render' ), '1.0', true );
    wp_add_inline_script( 'wpide-block-sibling-pages', <<<'JS'
( function ( wp ) {
    var el = wp.element.createElement;
    wp.blocks.registerBlockType( 'wpide/sibling-pages', {
        apiVersion: 3,
        title: 'Pages in This Section',
        icon: 'list-view',
        category: 'theme',
        usesContext: [ 'postId' ],
        edit: function ( props ) {
            return el( 'div', wp.blockEditor.useBlockProps(),
                el( wp.serverSideRender, { block: 'wpide/sibling-pages', urlQueryArgs: { post_id: props.context.postId || 0 } } )
            );
        },
        save: function () { return null; }
    } );
} )( window.wp );
JS
    );

    register_block_type( 'wpide/sibling-pages', array(
        'api_version'           => 3,
        'title'                 => 'Pages in This Section',
        'category'              => 'theme',
        'uses_context'          => array( 'postId' ),
        'editor_script_handles' => array( 'wpide-block-sibling-pages' ),
        'render_callback'       => function ( $attributes, $content, $block ) {
            $page_id = ! empty( $block->context['postId'] ) ? (int) $block->context['postId'] : ( isset( $_GET['post_id'] ) ? absint( $_GET['post_id'] ) : get_the_ID() );
            if ( ! $page_id || 'page' !== get_post_type( $page_id ) ) {
                return '';
            }

            $parent = (int) wp_get_post_parent_id( $page_id );
            $pages  = get_pages( array(
                'parent'      => $parent ? $parent : $page_id,
                'sort_column' => 'menu_order,post_title',
            ) );

            if ( ! $pages ) {
                return '';
            }

            $items = '';
            foreach ( $pages as $page ) {
                $current = (int) $page->ID === $page_id;
                $items  .= sprintf(
                    '<li%s><a href="%s"%s>%s</a></li>',
                    $current ? ' class="is-current"' : '',
                    esc_url( get_permalink( $page ) ),
                    $current ? ' aria-current="page"' : '',
                    esc_html( get_the_title( $page ) )
                );
            }

            $label = $parent ? get_the_title( $parent ) : get_the_title( $page_id );

            return sprintf( '<nav %s aria-label="%s"><ul>%s</ul></nav>', get_block_wrapper_attributes( array( 'class' => 'wpide-sibling-pages' ) ), esc_attr( $label ), $items );
        },
    ) );
} );