rust: use nightly-2020-03-25

[benma]

This is to be able to use async/await syntax, which was merged a few
days ago into nightly for no_std:
rust-lang/rust#69033.

This feature will be in beta in April and stable in June, at which
point we can start to use those channels again.

rust-toolchain file is added as a sanity check or for devs/users not
using Docker.

[benma]

Travis running here: https://travis-ci.org/github/digitalbitbox/bitbox02-firmware/builds/666704674

[x1ddos]

The rust-toolchain is very helpful! Could we do something like this?

COPY rust-toolchain /tmp/
RUN ... | CARGO_HOME=/opt/cargo sh -s -- --default-toolchain $(cat /tmp/rust-toolchain) -y

So to attempt to keep them in sync.

[benma]

Can be fragile, e.g. if someone slips in a newline in there, or deletes the file, it will break the docker build without anyone noticing

[x1ddos]

Sure. Someone could also update Dockerfile while forgetting to update rust-toolchain or the other way around. :)
Either way it fine with me!

[NickeZ]

With this change we technically don't need the RUSTC_BOOTSTRAP=1 any more. Any thoughts on removing that?

[benma]

With this change we technically don't need the RUSTC_BOOTSTRAP=1 any more. Any thoughts on removing that?

I'd still keep it with the hope of going beta->stable in the next months. Let's see if we can resist the temptation of nightly :D

[x1ddos]

LGTM

[NickeZ]

I would prefer that you cat the rust-toolchain file before approving this PR as @x1ddos wrote.

[benma]

I would prefer that you cat the rust-toolchain file before approving this PR as @x1ddos wrote.

I'm not for it:

Can be fragile, e.g. if someone slips in a newline in there, or deletes the file, it will break the docker build without anyone noticing

[benma]

Instead of rust-toolchain, i could add an ENV var to the dockerfile and use it in RUSTUP_TOOLCHAIN? https://github.com/rust-lang/rustup#override-precedence

Downside: works only with CMakeLists, not when running cargo test directly.

[x1ddos]

Can be fragile, e.g. if someone slips in a newline in there, or deletes the file, it will break the docker build without anyone noticing

TBH that's what code reviews and CIs are for :)

If RUSTUP_TOOLCHAIN works as an alternative, why not. I'd imagine something like:

docker build ... -e RUSTUP_TOOLCHAIN=$(cat rust-toolchain)

but it's equivalent to the other solution anyway.

[x1ddos]

Ah sorry, forget about docker build -e.... I don't know what I was thinking.

[x1ddos]

Can be fragile, e.g. if someone slips in a newline in there, or deletes the file, it will break the docker build without anyone noticing

TBH that's what code reviews and CIs are for :)

Plus, if someone submits a change to update rust-toolchain, I'd expect them to also run with it manually to verify it works.

[NickeZ]

Solve it any way you want, this string: nightly-2020-03-25 should only be in one place in the project.

[benma]

Ok did the cat thing