I find it doubtful that's all developed internally at Google; it's plausible that they pull in a lot of third-party code to make things easy on themselves. See

I find it doubtful that's all developed internally at Google; it's plausible that they pull in a lot of third-party code to make things easy on themselves. See, e.g., https://github.com/golang/go/issues/1605 https://github.com/golang/go/issues/1605