_inject_theme_attribute_in_block_template_content() WordPress Function

function _inject_theme_attribute_in_block_template_content( $template_content ) {
	$has_updated_content = false;
	$new_content         = '';
	$template_blocks     = parse_blocks( $template_content );

	$blocks = _flatten_blocks( $template_blocks );
	foreach ( $blocks as &$block ) {
		if (
			'core/template-part' === $block['blockName'] &&
			! isset( $block['attrs']['theme'] )
		) {
			$block['attrs']['theme'] = wp_get_theme()->get_stylesheet();
			$has_updated_content     = true;
		}
	}

	if ( $has_updated_content ) {
		foreach ( $template_blocks as &$block ) {
			$new_content .= serialize_block( $block );
		}

		return $new_content;
	}

	return $template_content;
}