Consider include-what-you-use (IWYU) tooling

[rjhuijsman]

Include What You Use (IWYU) is a tool-enforced policy that brings many benefits to C++ development.

Unfortunately, it's pretty hard to set up the IWYU tool, and I've not found good examples of anyone properly combining it with Bazel. That said, it shares some design features with clang-tidy, which we're already bringing into our standard toolkit.

Shall we also introduce IWYU?

CC @benh @while-false

[while-false]

I'd be up for it, but in terms of priority I would see it as a first step to get clang-tidy to play ball with bazel. Without having tried IWYU, I'd expect we'll run into a lot of the same issues with include paths and flags.

[benh]

I would LOVE this!