I have a very large macro instantiation, which takes 4 or 5 hours to compile with Rust 1.40, so I'm looking to improve this unreasonably long build time.  The macro wasn't always this slow to build, it seems to have gotten slower with newer versions of Rust, although I haven't pinpointed the exact point it regressed, it was always still slower than I would have liked (I recall it was around 30 minutes in earlier versions, still uncomfortably long for new contributors). I have avoided modifying t...