[Question] does fenix support `rust-toolchain` file?

[ghost]

As a Rust developer I declare a project's toolchain in a toolchain file.

Does fenix support this file or would I need to copy the contents of that file into my flake.nix?

Thanks!

[figsoda]

Yes! fenix provides fromToolchainFile, it supports both rust-toolchain and rust-toolchain.toml

you can use it like this

fromToolchainFile {
  file = ./rust-toolchain.toml;
  sha256 = lib.fakeSha256;
}

or this (impure without sha256)

fromToolchainFile { dir = ./.; }

[ghost]

Sweet, thanks for the documentation @figsoda. I'll close. As an aside, you may find my discourse question about which Rust overlay to prefer interesting.

[kevinboulain]

rust-gpu uses a rust-toolchain.toml file.

If I use rustup like this (following these instructions):

git clone https://github.com/EmbarkStudios/rust-gpu
cd rust-gpu
cat > shell.nix << EOF
let
  pkgs = import <nixpkgs> {};
  fenix = (import (fetchTarball "https://github.com/nix-community/fenix/archive/main.tar.gz") {});
in
pkgs.mkShell rec {
  # spirv-tools-sys compiles with -Werror and that breaks on _FORTIFY_SOURCE
  # without an optimization level. OPT_LEVEL might or might not work.
  # https://github.com/NixOS/nixpkgs/issues/60919
  hardeningDisable = [ "fortify" ];

  RUST_BACKTRACE = 1;
  # Necessary to find libvulkan.so.1 (RUST_LOG=wgpu_hal=debug).
  LD_LIBRARY_PATH = pkgs.lib.makeLibraryPath buildInputs;

  nativeBuildInputs = with pkgs; [
    rustup
  ];

  buildInputs = with pkgs; [
    # For libvulkan.so.1 (RUST_LOG=wgpu_hal=debug).
    vulkan-loader
    # X
    xorg.libX11 xorg.libXcursor xorg.libXi xorg.libXrandr
    # Wayland
    # https://github.com/gfx-rs/wgpu/issues/2519
    # libxkbcommon wayland
  ];
}
EOF
nix-shell
cargo build

It builds.

But if I replace rustup with fenix:

git clone https://github.com/EmbarkStudios/rust-gpu
cd rust-gpu
cat > shell.nix << EOF
let
  pkgs = import <nixpkgs> {};
  fenix = (import (fetchTarball "https://github.com/nix-community/fenix/archive/main.tar.gz") {});
in
pkgs.mkShell rec {
  # spirv-tools-sys compiles with -Werror and that breaks on _FORTIFY_SOURCE
  # without an optimization level. OPT_LEVEL might or might not work.
  # https://github.com/NixOS/nixpkgs/issues/60919
  hardeningDisable = [ "fortify" ];

  RUST_BACKTRACE = 1;
  # Necessary to find libvulkan.so.1 (RUST_LOG=wgpu_hal=debug).
  LD_LIBRARY_PATH = pkgs.lib.makeLibraryPath buildInputs;

  nativeBuildInputs = with pkgs; [
    (fenix.fromToolchainFile { dir = ./.; })
  ];

  buildInputs = with pkgs; [
    # For libvulkan.so.1 (RUST_LOG=wgpu_hal=debug).
    vulkan-loader
    # X
    xorg.libX11 xorg.libXcursor xorg.libXi xorg.libXrandr
    # Wayland
    # https://github.com/gfx-rs/wgpu/issues/2519
    # libxkbcommon wayland
  ];
}
EOF
nix-shell
cargo build

I'll hit https://github.com/EmbarkStudios/rust-gpu/issues/1047:

error[E0599]: no function or associated item named `from_u128` found for type parameter `P` in the current scope
   --> crates/rustc_codegen_spirv/src/abi.rs:867:26
    |
861 |             fn const_int_value<'tcx, P: FromPrimitive>(
    |                                      - function or associated item `from_u128` not found for this type parameter
...
867 |                 match P::from_u128(value) {
    |                          ^^^^^^^^^
    |                          |
    |                          function or associated item not found in `P`
    |                          help: there is an associated function with a similar name: `from_u8`

I wanted to use the same version but with additional components, something along the lines of:

((fenix.toolchainOf {                                                                                                                   
  channel = "nightly";                                                                                                                  
  date = "2023-03-04";                                                                                                                  
  sha256 = "sha256-s9/H9SHOZJdYyJsiqT+cMTspY0SzaaF64ydLiTSfDqQ=";
}).withComponents [
  "cargo"
  "clippy"
  "llvm-tools-preview"
  "rust-analyzer"
  "rust-src"
  "rustc"
  "rustc-dev"
  "rustfmt"
])

Which should be a superset of their rust-toolchain.toml but obviously, I'm misunderstanding something.

[figsoda]

https://github.com/nix-community/fenix/commit/b4616f7fa72bcda1b48511e4043d6813aa2d953b should be able to fix it once it gets into main

[kevinboulain]

Thanks!