rust: replace fenix with rust-overlay allow specifying rust version

[eyJhb]

Adds basic support for specifying the version of the rust toolchain you want to use.
This change moves away from using fenix, to instead using rust-overlay.

It seems to work just fine, and is somewhat minimal invasive.
TODO:

• Not sure what to do about removing the renamed option, and then using it again.. Is there any better ways?
• Make targets work, nothing compiles atm.

Example:

{
  languages.rust = {
    enable = true;

    # latest stable version
    # channel = "stable";

    # nightly version
    # channel = "nightly";
    # version = "2024-06-20";

    # specific stable version
    # channel = "stable";
    # version = "1.70.0";

  };
}

[eyJhb]

I fixed targets not working, but it's not pretty. I copied combine.nix from fenix, and not sure what the better way is.

[domenkozar]

We should error out of channel values in version, to properly instruct how to migrate for users that are still using version for channels.

[domenkozar]

FYI, both rust examples fail in CI.

[domenkozar]

@eyJhb would be great to get this in!

[eyJhb]

We should error out of channel values in version, to properly instruct how to migrate for users that are still using version for channels.

I am unsure how this should be done, can you give me any pointers? Tests and docs should be fixed now. The failing test on main should also be working now (it seemed to be failing before).

[domenkozar]

Nice! I think it needs pre-commit run -a

[eyJhb]

Nice! I think it needs pre-commit run -a

Should be done now! :)

[domenkozar]

It seems like rust-cross-wasm failed with clippy hook:

0000.12:     Checking devenv-tasks v0.1.0 (/run/github-runner/cachix-x86_64-linux-1/devenv/devenv/devenv-tasks)
0000.12: error: the `-Z unstable-options` flag must also be passed to enable the flag `check-cfg`
0000.12: 
0000.12: error: could not compile `devenv-tasks` (lib)
0000.12: warning: build failed, waiting for other jobs to finish...
0000.12: 

[domenkozar]

Ah, seems that's an existing bug using git-hooks. I'll test this soon!

[eyJhb]

@domenkozar rebased ! :)