Add an example project that has a workspace with a couple of crates, where one of the crates has a compile-test

[gnzlbg]

There doesn't seem to be any tests checking that this library works for workspaces, and there are no disclaimers about this in the readme nor any docs.

[laumann]

There is none such, and this has never really been a priority. I have limited experience with workspaces (although I'm learning a lot more these days).