core/pkgs/build-support/fetchcvs/default.nix

# example tags:
# date="2007-20-10"; (get the last version before given date)
# tag="<tagname>" (get version by tag name)
# If you don't specify neither one date="NOW" will be used (get latest)

{
  stdenvNoCC,
  cvs,
  openssh,
  lib,
}:

lib.makeOverridable (
  {
    cvsRoot,
    module,
    tag ? null,
    date ? null,
    sha256,
  }:

  stdenvNoCC.mkDerivation {
    name = "cvs-export";
    builder = ./builder.sh;
    nativeBuildInputs = [
      cvs
      openssh
    ];

    outputHashAlgo = "sha256";
    outputHashMode = "recursive";
    outputHash = sha256;

    inherit
      cvsRoot
      module
      sha256
      tag
      date
      ;
  }
)