Installs `rustc` from nixpkgs when already installed

[pseudoparenchymatous]

I am using fenix as my rust overlay; installed it in my dev-shell using nativeBuildInputs. But when I run nix build, it reinstalls the toolchain (i.e. rustc) from nixpkgs.

And if I remove nixpkgs from my inputs, nix build behaves as expected and builds the crate.

[pseudoparenchymatous]

Disable nixpkgs in inputs

nix build/nix run without problem

[pseudoparenchymatous]

Fixed it by overlaying directly the rustc and cargo packages from nixpkgs

[pseudoparenchymatous]

Nope. Overlaying rustc and cargo directly doesn't seem to be the correct way. It breaks other packages from nixpkgs that may rely on nixpkgs' derivation of rustc/cargo.

So what's the right way of telling crate2nix to use/download/install rustc/cargo from another source other than nixpkgs?

[pseudoparenchymatous]

Fixed it with

let
  minimal-toolchain = fenix.packages.${system}.stable.minimalToolchain;
  cargoNix = pkgs.callPackage ./Cargo.nix {
    buildRustCrateForPkgs = pkgs: pkgs.buildRustCrate.override {
      rustc = minimal-toolchain;
      cargo = minimal-toolchain;      
    };
  };
in packages.default = cargoNix.rootCrate.build;