Xargo does not work with rust-src about nixpkgs-mozilla HOT 3 CLOSED

let
  moz_overlay = import (builtins.fetchTarball https://github.com/mozilla/nixpkgs-mozilla/archive/master.tar.gz);
  nixpkgs = import <nixpkgs> { overlays = [ moz_overlay ]; };
in
  with nixpkgs;
  stdenv.mkDerivation {
    name = "project";
    buildInputs = [
      (rustChannels.nightly.rust.override {
        targets = [ "thumbv7m-none-eabi" ];
        extensions = [ "rust-std" "rustfmt-preview" ];
      })
      gcc-arm-embedded
    ];
  }

(rustChannels.nightly.rust.override { extensions = [ "rust-src" ]; })

with import <nixos> {};
runCommand "dummy" {
  buildInputs = [
    (rustChannels.nightly.rust.override { extensions = [ "rust-src" ]; })
    gcc-arm-embedded
  ];
} ""