Closure contains Rust tool dependencies if using rust-src component in (rust-overlay) toolchain

[b-zee]

When I was copying the resulting closure over SSH I noticed that the closure had (large) Rust compiler dependencies.

I am using a basic flake.nix that loads rust-toolchain.toml with rust-overlay:

{
  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
    flake-utils.url = "github:numtide/flake-utils";
    naersk.url = "github:nix-community/naersk";
    rust-overlay.url = "github:oxalica/rust-overlay";
    rust-overlay.inputs.nixpkgs.follows = "nixpkgs";
  };

  outputs = { self, nixpkgs, flake-utils, naersk, rust-overlay }:
    flake-utils.lib.eachDefaultSystem (system:
      let
        overlays = [ (import rust-overlay) ];
        pkgs = import nixpkgs { inherit system overlays; };
        toolchain = pkgs.rust-bin.fromRustupToolchainFile ./rust-toolchain.toml;
        naersk' = pkgs.callPackage naersk { cargo = toolchain; rustc = toolchain; clippy = toolchain; };
      in
      {
        # For `nix build` & `nix run`:
        defaultPackage = naersk'.buildPackage {
          src = ./.;
        };
      }
    );
}

And the following rust-toolchain.toml:

[toolchain]
channel = "nightly-2025-01-12"
components = [ "rust-src", "rustfmt" ]
profile = "default"

I get the following dependencies:

$ nix build && nix-store --query ./result --requisites
/nix/store/17v0ywnr3akp85pvdi56gwl99ljv95kx-gcc-14-20241116-libgcc
/nix/store/xcqcgqazykf6s7fsn08k0blnh0wisdcl-libunistring-1.3
/nix/store/34z2792zyd4ayl5186vx0s98ckdaccz9-libidn2-2.3.7
/nix/store/acfkqzj5qrqs88a4a6ixnybbjxja663d-xgcc-14-20241116-libgcc
/nix/store/65h17wjrrlsj2rj540igylrx7fqcd6vq-glibc-2.40-36
/nix/store/1c6bmxrrhm8bd26ai2rjqld2yyjrxhds-glibc-2.40-36-bin
/nix/store/kryrg7ds05iwcmy81amavk8w13y4lxbs-gmp-6.3.0
/nix/store/qs22aazzrdd4dnjf9vffl0n31hvls43h-mpfr-4.2.1
/nix/store/2a3anh8vl3fcgk0fvaravlimrqawawza-libmpc-1.3.1
/nix/store/2phvd8h14vwls0da1kmsxc73vzmhkm3b-util-linux-minimal-2.39.4-lib
/nix/store/lydgmfxkkgxn7p6rhp11cxnmq62wz237-libgpg-error-1.50
/nix/store/2qafk9zc2xf4p8ip66q59shwn6sbbaw3-libgcrypt-1.10.3-lib
/nix/store/3j1p598fivxs69wx3a657ysv3rw8k06l-pcre2-10.44
/nix/store/bpq1s72cw9qb2fs8mnmlw6hn2c7iy0ss-gcc-14-20241116-lib
/nix/store/a2byxfv4lc8f2g5xfzw8cz5q8k05wi29-gmp-with-cxx-6.3.0
/nix/store/a9jgnlhkjkxav6qrc3rzg2q84pkl2wvr-attr-2.5.2
/nix/store/cf7gkacyxmm66lwl5nj6j6yykbrg4q5c-acl-2.3.2
/nix/store/4s9rah4cwaxflicsk5cndnknqlk9n4p3-coreutils-9.5
/nix/store/5mh7kaj2fyv8mk4sfq1brwxgc02884wi-bash-5.2p37
/nix/store/cqlaa2xf6lslnizyj9xqa8j0ii1yqw0x-zlib-1.3.1
/nix/store/qbry6090vlr9ar33kdmmbq2p5apzbga8-expand-response-params
/nix/store/89p14s7lp4v48j2mdijbd56pnk90x0ms-rustc-1.86.0-nightly-2025-01-12-x86_64-unknown-linux-gnu
/nix/store/6542ml6l448yr2m740xjmd31f9jiw4w9-rustfmt-preview-1.86.0-nightly-2025-01-12-x86_64-unknown-linux-gnu
/nix/store/aaj9rh2v78njlmi6pyhdfyy4mzl5b8ys-libselinux-3.7
/nix/store/r04wysx6yl7ys1rdv1b1lih6in1810r0-libffi-3.4.6
/nix/store/rb870mk51kxlxq9crkldzs8n4vwr9sk4-glib-2.82.1
/nix/store/ji9vn0l5xpcvnbysc9xjsysmj07x5w8f-libsecret-0.21.4
/nix/store/a78ym5yrpjr4xl9frd4xsf79k5bwz093-cargo-1.86.0-nightly-2025-01-12-x86_64-unknown-linux-gnu
/nix/store/dp6s2s3dza9818kf100hx1qqk3xf6sam-clippy-preview-1.86.0-nightly-2025-01-12-x86_64-unknown-linux-gnu
/nix/store/fqyhlnrjgj35kxqbc0657kpa7ish5740-rust-docs-1.86.0-nightly-2025-01-12-x86_64-unknown-linux-gnu
/nix/store/g2vnr5ppwxn981iab0vhi4gma1n1f8qs-rust-src-1.86.0-nightly-2025-01-12-x86_64-unknown-linux-gnu
/nix/store/jpphwwn9j2zx929ilia3bfbn9b0ly9kc-rust-std-1.86.0-nightly-2025-01-12-x86_64-unknown-linux-gnu
/nix/store/aap6cq56amx4mzbyxp2wpgsf1kqjcr1f-gnugrep-3.11
/nix/store/pc74azbkr19rkd5bjalq2xwx86cj3cga-linux-headers-6.12
/nix/store/kj8hbqx4ds9qm9mq7hyikxyfwwg13kzj-glibc-2.40-36-dev
/nix/store/xmbv8s4p4i4dbxgkgdrdfb0ym25wh6gk-isl-0.20
/nix/store/l89iqc7am6i60y8vk507zwrzxf0wcd3v-gcc-14-20241116
/nix/store/df2a8k58k00f2dh2x930dg6xs6g6mliv-binutils-2.43.1-lib
/nix/store/j7p46r8v9gcpbxx89pbqlh61zhd33gzv-binutils-2.43.1
/nix/store/srcmmqi8kxjfygd0hyy42c8hv6cws83b-binutils-wrapper-2.43.1
/nix/store/xcn9p4xxfbvlkpah7pwchpav4ab9d135-gcc-wrapper-14-20241116
/nix/store/5rpgz0pkrs0s99sbm61nliacyq1mrx5z-rust-default-1.86.0-nightly-2025-01-12
/nix/store/817pyv9aw873svllk65dq3iivibsgnhq-nebby-0.1.0

---

I was able to solve this by removing the rust-src component from the toolchain:

[toolchain]
 channel = "nightly-2025-01-12"
-components = [ "rust-src", "rustfmt" ]
+components = [ "rustfmt" ]
 profile = "default"

$ nix build && nix-store --query ./result --requisites
/nix/store/17v0ywnr3akp85pvdi56gwl99ljv95kx-gcc-14-20241116-libgcc
/nix/store/xcqcgqazykf6s7fsn08k0blnh0wisdcl-libunistring-1.3
/nix/store/34z2792zyd4ayl5186vx0s98ckdaccz9-libidn2-2.3.7
/nix/store/acfkqzj5qrqs88a4a6ixnybbjxja663d-xgcc-14-20241116-libgcc
/nix/store/65h17wjrrlsj2rj540igylrx7fqcd6vq-glibc-2.40-36
/nix/store/bpq1s72cw9qb2fs8mnmlw6hn2c7iy0ss-gcc-14-20241116-lib
/nix/store/f9r9z1xfr1pznjrha1scny7fi1iccmjw-nebby-0.1.0

---

A workaround by overriding the components in the flake.nix (as I need the rust-src for my editor via nix dev shell):

-        toolchain = pkgs.rust-bin.fromRustupToolchainFile ./rust-toolchain.toml;
+        toolchain = pkgs.rust-bin.fromRustupToolchain ((builtins.fromTOML (builtins.readFile ./rust-toolchain.toml)).toolchain // { "components" = [ ]; });