build: Add Rust

[cgwalters]

So far we have lots of shell script, some Python, Go from mantle...
clearly, we need to add Rust!

More seriously so...I like the language, I am not excited about
writing more dynamically typed and slow shell script/Python.

There's a definite argument for Go, since we could share code
with Mantle. I personally like Rust a lot though...but
this is an RFE to see how people feel.

My vision for this was that we could start implementing some of
the VM installation work in it, along with defining Serde
structs for the metadata, etc.

[dustymabe]

I honestly don't know. but it seems like we are going to make things real soupy real fast unless we strategize together on what we want to do with this thing.

My personal preference is being able to hack on it dynamically which makes python a good choice. I'm not worried about the "slowness" of python since I don't think it really makes a difference for this application.

[jlebon]

I'm a bit conflicted. Rust is awesome, but I'm more worried about potentially making it harder for others to contribute than making the build scripts faster (we're blocked on I/O from whatever we're spawning 99% of the time anyway). I agree we should move away from shell scripts though. So I guess I'm leaning more towards Python or Go?

[cgwalters]

OK, will leave it open a bit for any other votes. In the end it doesn't have to be exclusive.

One reason I had in mind to choose Rust or Go in particular is that the statically linked binary approach is easier to copy over into VMs we generate.

[cgwalters]

The intersection of the comments so far leans towards Python. I guess if no one else has any comments by e.g. tomorrow we'll go that way and close this PR.

[jlebon]

It's not exactly the same, though I'd be interested to hear from folks familiar with cork/plume re. writing this type of "glue code" in Python vs Go.

[cgwalters]

The main thing I dislike about Go for this is that for 99% of "build system code" like this, one simply wants to immediately exit on error. Throwing an exception is fine. The Go error handling is very verbosely annoying for this - notably worse than Python's exceptions or Rust's ? operator.

[dustymabe]

cc @ajeddeloh @dm0- @bgilbert - any input?

[dm0-]

I'd like to see Rust work here, but if the priority is making it accessible to more contributors and easier for casual hacking, Python is probably the best choice.

[bgilbert]

Yeah, for accessibility I'd prefer to see Python or Go.

[lucab]

I was away, thus I totally missed this and asked the exact same question today.

As @glevand highlighted, once we reach the size of coreos/scripts (~5k LoC of sh, quickly counted) refactoring and ongoing maintenance is a concern. I'd prefer something with static typing for that. If Rust is an entry-barrier, then I'd stick with Go.