Override compiler version

[vbrandl]

How can I override, which rustc version or branch (stable/beta/nightly) to use?

Also it would be cool, if crate2nix would check for rust-toolchain files which are used by rustup to pin a specific compiler version and or branch for a repository.

[kolloch]

You can override the rust compiler by overlays to the used nixpkgs.

I will investigate in making this easy...

[vbrandl]

Would be cool to mention this in the readme with an example.

I tried adding the mozilla overlay but I can't figure out, where do override the used compiler channel

[andir]

@vbrandl I am using the following pattern in an overlay:

self: super: {
   rustNightlyChannel = mozilla.rustChannelOf { date = "..."; channel = "..."; };
   rustNightly = self.rustNightlyChannel.rust.override { extensions = [ "rust-src" ]; };
   myBuildRustCrate = super.buildRustCrate.override { rustc = self.rustNightly; };
   myPkg = (self.callPackage ./Crate.nix { buildRustCrate = myBuildRustCrate; }).rootCrate.build;
}

(adopted from my actual, more complicated, version)

[vbrandl]

Thank you. I also found this one yesterday but I didn't come around to test it, yet: https://github.com/jD91mZM2/xidlehook/blob/master/default.nix

[cpcloud]

@kolloch @vbrandl Can this be closed?

[danieldk]

This answer is similar to @andir 's, but I just wanted to make explicit that you don't need to use an overlay.buildRustCrate, which is what the file generated by crate2nix uses, allows you to specify a whole Rust toolchain through the rust argument. This can be handy when you make a package set that others should also be able to use, without defining overlays locally.

This is an example of a derivation using a nightly compiler:

https://github.com/finalfusion/nix-packages/blob/cf8a4140d2359fb512608bde3c88ba410b5d94fb/pkgs/python-modules/finalfusion/default.nix

It's self-contained, so others can use the derivation directly.

Edit: nevermind, I was still on a crate2nix branch with PR #38, and I somehow misremembered that 184d3dd made this possible.

@kolloch maybe it's still worth pursuing this approach? It's more powerful than the defaultCrateOverrides argument introduced by 184d3dd. carnix also supports overriding buildRustCrate arguments. It's more intuitive than having to override buildRustCrate first and then passing the overrided buildRustCrate as an argument.

[vbrandl]

I wasn't able to test yet because I didn't need it anymore (since 1.39.0 landed in the unstable channel, I don't need a nightly compiler for async/await). This can be closed but I think it would be nice to have a documented example in the README that shows how to use the mozilla overlay

[kolloch]

@andir @vbrandl @danielk I added documentation for doing this "globally" here:

https://github.com/kolloch/crate2nix#choosing-a-rust-version

I discovered one caveat: I had to use "rust" (without the c suffix) for "rustc" with a recent version of the overlay because otherwise rustc wouldn't find the std sources.

Doing this globally is often what you want, I guess. Build all your stuff with the same rust compiler. But the individual approach also has merrit. Maybe you want to add that to the documentation? You would be welcome.

@danielk for making buildRustCrate more directly overridable, see #77. Tell me what you think! For "pkgs" it is not the right tool, though, since you also want to override it for all dependencies, correct?

[kolloch]

I will close this issue for now but will gladly accept documentation fixes/extensions.