A couple of hours worth of hacking to produce a UI for Cargo that presents a form of compilation progress as well as what's currently being compiled. Should give you a good idea about where the compiler is as part of a compilation!
cargo install cargo-fancy
Just insert fancy into any command you want fancified!
$ cargo fancy build
$ cargo fancy test
$ cargo fancy build --release -j3 --manifest-path foo/Cargo.toml
-Z
time-passes