src/vs/platform/files/common/files.ts/etag
export function etag(stat: { mtime: number | undefined; size: number | undefined }): string | undefined {
	if (typeof stat.size !== 'number' || typeof stat.mtime !== 'number') {
		return undefined;
	}

	return stat.mtime.toString(29) + stat.size.toString(31);
}