This is work from Jeremy Rubin integrated into our buildsystem. It allows for rust code to be used directly inside of Bitcoin Core. In its current form, it demonstrates calling a single hello_world function from rust code.
This is not intended to be merged as-is, but instead to serve as a reference for anyone who might be interested in trying out some rust code inside of Bitcoin Core. I have no idea what works. I have lots of questions about debugging, threading, etc. But instead of trying to hack and document how things work, we thought it'd be fun for everyone to be able to poke at it and scratch our heads together :). If something interesting comes out of it, a discussion about merging can happen then.
It is surprisingly functional. The rust tools are impeccable. I would've thought this would be a project that would take months/years, but the rust devs have done such a good job that mostly everything already just works. The gitian descriptors have been modified to actually incorporate working rust code. All of our currently supported platforms seem to already work (even macOS cross!) with the exception of 32bit windows and ancient linux distros. The specific issues are documented in the gitian descriptors. For now, Gitian needs net access and a larger disk volume, but those are both very temporary issues
Why rust? I don't know. Maybe not. But I think it's a fair assumption to say that Rust code will eventually end up in Bitcoin Core as the result of adding a new dependency. Adoption is happing quickly. So, I think it prudent to look ahead and not only be prepared, but actively help usher it in. Already I have a few things that I would like to work on and upstream to rust-lang to make our integration nicer, and I assume that more will be uncovered as it actually gets used.
Anybody have any fun ideas?