amp-paired-block-visibility.php

<?php
/**
 * AMP Paired Block Visibility plugin initialization file.
 *
 * @package   AMP_Paired_Block_Visibility
 * @author    Weston Ruter, Google
 * @license   GPL-2.0-or-later
 * @copyright 2019 Google Inc.
 *
 * @wordpress-plugin
 * Plugin Name: AMP Paired Block Visibility
 * Plugin URI: https://gist.github.com/westonruter/0769f147e021e0ebfcb04a084987483a
 * Description: For paired AMP sites (in Transitional or Reader template mode), hide any blocks with the <code>noamphtml</code> CSS class supplied via advanced block settings. Conversely, hide any blocks with the <code>amphtml</code> class name present on non-AMP pages.
 * Version: 0.1
 * Author: Weston Ruter, Google
 * Author URI: https://weston.ruter.net/
 * License: GNU General Public License v2 (or later)
 * License URI: http://www.gnu.org/licenses/gpl-2.0.html
 * Gist Plugin URI: https://gist.github.com/westonruter/0769f147e021e0ebfcb04a084987483a
 */

namespace AMP_Paired_Block_Visibility;

add_filter(
	'render_block',
	function ( $block_content, $block ) {
		if ( ! function_exists( 'is_amp_endpoint' ) || ! isset( $block['attrs']['className'] ) ) {
			return $block_content;
		}

		$is_amp_endpoint = is_amp_endpoint();
		if (
			( $is_amp_endpoint && preg_match( '/(^|\s)noamphtml(\s|$)/', $block['attrs']['className'] ) )
			||
			( ! $is_amp_endpoint && preg_match( '/(^|\s)amphtml(\s|$)/', $block['attrs']['className'] ) )
		) {
			return '';
		}

		return $block_content;
	},
	10,
	2
);

Installation instructions: https://gist.github.com/westonruter/6110fbc4bef0c4b8c021a112012f7e9c

Usage:

Frontend results: