Note that it wasn't a simple cargo update, but an update between two semver incompatible releases of the futures crate, from 0.1 which supported edition 2015 and provided combinators, to 0.3 which was built on the async/await feature, and required its use, because the combinators were removed. I guess it would have been hard to provide them compatibly to async/await but I'm not sure about it. Anyways, they weren't available, and as async/await is not available on the 2015 edition, I had to update the edition of the crate. The code got a lot simpler thanks to async/await so I'm very thankful for its existence.