async function process_markup(process, source) {
	const processed = await process({
		content: source.source,
		filename: source.filename
	});
	if (processed) {
		return {
			string: processed.code,
			map: processed.map
				? // TODO: can we use decode_sourcemap?
					typeof processed.map === 'string'
					? JSON.parse(processed.map)
					: processed.map
				: undefined,
			dependencies: processed.dependencies
		};
	} else {
		return {};
	}
}
@param {MarkupPreprocessor} process
@param {Source} source