add rust-toolchain.toml for the host program

[onur-ozkan]

What is the problem?

When creating projects with cargo nexus host $project, nexus generates rust-toolchain.toml file for the guest program but not for the host program.

This leads to two issues:

1. Users needs to manually install the RISC-V target for the toolchain (cc development experience improvements #256).
2. If the default toolchain differs from the one used by the guest program, it will result in installing the RISC-V target twice (once for the guest and once for the host).

What do you want to happen?

Include the same rust-toolchain.toml file in the host program.

Existing alternatives

N/A

Additional notes

N/A

[danielmarinq]

Thanks @onur-ozkan, @slumber can you take a look?

[onur-ozkan]

Moving guest rust-toolchain.toml to the workspace level should be enough too. It doesn't need to be duplicated for per project.

[slumber]

Eventually we want to unfreeze the toolchain, it's probably possible already, I need to check

[onur-ozkan]

FWIW you can remove the channel section from rust-toolchain.toml to unfreeze the toolchain version while keeping the targets field to automatically handle targets for the user's toolchain.

[slumber]

Guest programs required specific version, otherwise the VM used to panic with Jolt. This needs to be double checked.

Freezing the toolchain for host isn't proper solution, cargo install will ignore it and users will bump into it anyway.

UPD: jolt still requires frozen toolchain

[onur-ozkan]

Interesting. I don't know much about the build internals of this project, but it seems that the rust-toolchain.toml file on the guest side isn't being respected.

The toolchain configuration for the guest side looks like this:

[toolchain]
channel = "1.77.0"
targets = ["riscv32i-unknown-none-elf"]

However, I don't have 1.77.0 installed on my system, yet I can still run the program with cargo run -r.

[slumber]

You can try

cargo nexus prove --impl=jolt

with toolchain file present and removed.

[onur-ozkan]

I see, so it's used for certain builds. I still think (as a user) it would be nice to have a rust-toolchain.toml file (without the channel field to avoid locking the toolchain) on the host side. This would eliminate the need to manually install the RISC-V target as rustup will handle that automatically once the build starts.