I recently migrated a small/medium-sized crate from Futures 0.1 to 0.3. It was fairly easy, but there were some tricky bits and some things that were not well documented, so I think it is worth me writing up my experience. The crate I migrated is the Rust client for the TiKV database. It is about 5500 LoC and uses futures fairly heavily (because it communicates with TiKV using gRPC and the interface to that is async).
