{ pkgs, ... }:

let
  hgRepo = builtins.path { path = ./.hg; name = "depot-hg"; };
  changesetDeriv = pkgs.runCommandLocal "depot-version" {
    HG_REPO = hgRepo;
    MERCURIAL = pkgs.mercurial;
  } ''
    export HGPLAIN=
    mytmp=$(mktemp -d)
    pushd $mytmp
    ln -s $HG_REPO .hg
    echo -n "depot-$($MERCURIAL/bin/hg id --id -r.)" > $out
    popd
    rm -rf $mytmp
  '';
in
  builtins.readFile changesetDeriv