detect-non-block-pages.php

<?php

/**
 * Runs on shutdown.
 * This prevents any performance issues since it runs _after_ the page
 * has finished loading and has already been served.
 */
add_action( 'shutdown', function() {

	// Bail if not a singular entity.
	if ( ! is_single() && ! is_singular() && ! is_page() ) {
		return;
	}

	// Sanity check: Bail if the has_blocks() function doesn't exist.
	if ( ! function_exists( 'has_blocks' ) ) {
		return;
	}

	// Get an array of posts-IDs without blocks from the DB.
	$no_blocks = (array) get_option( 'post_without_blocks', [] );

	$the_id     = get_the_ID();
	$has_blocks = has_blocks( $the_id );

	// If the post doesn't have blocks, add it to the array.
	if ( ! in_array( $the_id, $no_blocks ) && ! $has_blocks ) {
		$no_blocks[] = $the_id;
		update_option( 'post_without_blocks', $no_blocks );
	}

	// If the post has blocks and was in the array, remove it.
	if ( in_array( $the_id, $no_blocks ) && $has_blocks ) {
		$key = array_search( $the_id, $no_blocks );
		unset( $no_blocks[ $key ] );
		update_option( 'post_without_blocks', $no_blocks );
	}
} );