anchor.diff:    # this hermetic
     buildPhase = ''
       runHook preBuild
  -    HOME=. rebar3 do update, compile
  +    HOME=. rebar3 compile
       ${if compilePorts then ''
       HOME=. rebar3 pc compile
       '' else ''''}
  
positive.code:     };
    in ''
      runHook preConfigure
      mkdir -p _build/default/{lib,plugins}/
      ${concatMapStrings (dep: ''
        header "linking erlang dependency ${dep}"
        ln -s "${dep}" "_build/default/lib/${dep.packageName}"
  
negative.code: { stdenv, erlang, rebar3, openssl, libyaml, fetchurl, fetchFromGitHub }:
  
  { name, version, sha256
  , hexPkg ? name
  