wpseek.com
A WordPress-centric search engine for devs and theme authors

function wp_img_tag_add_auto_sizes( string $image ): string {
	/**
	 * Filters whether auto-sizes for lazy loaded images is enabled.
	 *
	 * @since 6.7.1
	 *
	 * @param boolean $enabled Whether auto-sizes for lazy loaded images is enabled.
	 */
	if ( ! apply_filters( 'wp_img_tag_add_auto_sizes', true ) ) {
		return $image;
	}

	$processor = new WP_HTML_Tag_Processor( $image );

	// Bail if there is no IMG tag.
	if ( ! $processor->next_tag( array( 'tag_name' => 'IMG' ) ) ) {
		return $image;
	}

	// Bail early if the image is not lazy-loaded.
	$loading = $processor->get_attribute( 'loading' );
	if ( ! is_string( $loading ) || 'lazy' !== strtolower( trim( $loading, " \t\f\r\n" ) ) ) {
		return $image;
	}

	/*
	 * Bail early if the image doesn't have a width attribute.
	 * Per WordPress Core itself, lazy-loaded images should always have a width attribute.
	 * However, it is possible that lazy-loading could be added by a plugin, where we don't have that guarantee.
	 * As such, it still makes sense to ensure presence of a width attribute here in order to use `sizes=auto`.
	 */
	$width = $processor->get_attribute( 'width' );
	if ( ! is_string( $width ) || '' === $width ) {
		return $image;
	}

	$sizes = $processor->get_attribute( 'sizes' );

	// Bail early if the image is not responsive.
	if ( ! is_string( $sizes ) ) {
		return $image;
	}

	// Don't add 'auto' to the sizes attribute if it already exists.
	if ( wp_sizes_attribute_includes_valid_auto( $sizes ) ) {
		return $image;
	}

	$processor->set_attribute( 'sizes', "auto, $sizes" );
	return $processor->get_updated_html();
}