anchor.diff:      paths = envPaths;
       pathsToLink = [ "/lib" ];
   
  -    postBuild = ''
  -      ${ruby}/bin/ruby ${./gen-bin-stubs.rb} \
  -        "${ruby}/bin/ruby" \
  -        "${confFiles}/Gemfile" \
  -        "$out/${ruby.gemPath}" \
  -        "${bundler}/${ruby.gemPath}" \
  -        ${lib.escapeShellArg binPaths} \
  -        ${lib.escapeShellArg groups}
  -    '' + lib.optionalString (postBuild != null) postBuild;
  +    postBuild = (genStubs binPaths) + lib.optionalString (postBuild != null) postBuild;
   
       meta = { platforms = ruby.meta.platforms; } // meta;
   
  
positive.code: 
    envPaths = lib.attrValues gems ++ lib.optional (!hasBundler) bundler;
  
    binPaths = if mainGem != null then [ mainGem ] ++ envPaths else envPaths;
  
    bundlerEnv = buildEnv {
      inherit ignoreCollisions;
  
negative.code: , gemfile ? null
  , lockfile ? null
  , gemset ? null
  , allBins ? false
  , ruby ? defs.ruby
  , gemConfig ? defaultGemConfig
  , postBuild ? null
  