create-block-theme/includes/create-theme/theme-patterns.php

<?php

class CBT_Theme_Patterns {
	public static function pattern_from_template( $template, $new_slug = null ) {
		$theme_slug      = $new_slug ? $new_slug : wp_get_theme()->get( 'TextDomain' );
		$pattern_slug    = $theme_slug . '/' . $template->slug;
		$pattern_content = <<<PHP
		<?php
		/**
		 * Title: {$template->slug}
		 * Slug: {$pattern_slug}
		 * Inserter: no
		 */
		?>
		{$template->content}
		PHP;

		return array(
			'slug'    => $pattern_slug,
			'content' => $pattern_content,
		);
	}

	public static function escape_alt_for_pattern( $html ) {
		if ( empty( $html ) ) {
			return $html;
		}
		$html = new WP_HTML_Tag_Processor( $html );
		while ( $html->next_tag( 'img' ) ) {
			$alt_attribute = $html->get_attribute( 'alt' );
			if ( ! empty( $alt_attribute ) ) {
				$html->set_attribute( 'alt', self::escape_text_for_pattern( $alt_attribute ) );
			}
		}
		return $html->__toString();
	}

	public static function escape_text_for_pattern( $text ) {
		if ( $text && trim( $text ) !== '' ) {
			$escaped_text = addslashes( $text );
			return "<?php esc_attr_e('" . $escaped_text . "', '" . wp_get_theme()->get( 'Name' ) . "');?>";
		}
	}

	public static function create_pattern_link( $attributes ) {
		$block_attributes = array_filter( $attributes );
		$attributes_json  = json_encode( $block_attributes, JSON_UNESCAPED_SLASHES );
		return '<!-- wp:pattern ' . $attributes_json . ' /-->';
	}

}