proto: better automated protobuf format checks

[jdef]

There's currently a check for line lengths greater than 72 chars. Ideally we'd have more robust, automated format checks across the board for protobuf files. I'd also like to see standard formatting for comments enforced by tooling.

I spent a while with sed and friends this afternoon but it's nowhere near up to the challenge (or maybe I'm not up to the challenge for doing this job w/ sed, awk, fmt, par, or whatever other non-proto format tooling is out there).

Searching around I found some related projects. I haven't investigated any of them. Maybe this could be a (re)starting point for later.

• https://github.com/DirkBrand/protobuf-code-formatter
• https://clang.llvm.org/docs/ClangFormat.html
• https://github.com/uber/prototool#prototool-format