core/pkgs/build-support/rust/fetchcrate.nix

{ lib, fetchzip, fetchurl }:

{ crateName ? args.pname, pname ? null
  # The `dl` field of the registry's index configuration
  # https://doc.rust-lang.org/cargo/reference/registry-index.html#index-configuration
, registryDl ? "https://crates.io/api/v1/crates", version, unpack ? true, ...
}@args:

assert pname == null || pname == crateName;

(if unpack then fetchzip else fetchurl) ({
  name = "${crateName}-${version}.tar.gz";
  url = "${registryDl}/${crateName}/${version}/download";
} // lib.optionalAttrs unpack { extension = "tar.gz"; }
  // removeAttrs args [ "crateName" "pname" "registryDl" "version" "unpack" ])