anchor.diff:       for the platform in question. */
     testOn = systems: f: {system ? builtins.currentSystem}:
       if pkgs.lib.elem system systems then f (allPackages {inherit system;}) else {};
  +
  +  /* Similar to the testOn function, but with an additional 'crossSystem'
  +   * parameter for allPackages, defining the target platform for cross builds */
  +  testOnCross = crossSystem: systems: f: {system ? builtins.currentSystem}:
  +    if pkgs.lib.elem system systems then f (allPackages {inherit system
  +                crossSystem;}) else {};
   
     /* Map an attribute of the form `foo = [platforms...]'  to `testOn
        [platforms...] (pkgs: pkgs.foo)'. */
  
positive.code:           pkgs.lib.addMetaAttrs { schedulingPriority = toString job.schedulingPriority; }
            (pkgs.lib.getAttrFromPath path pkgs);
        in testOn job.systems getPkg);
  
    /* Find all packages that have a meta.platforms field listing the
       supported platforms. */
  
negative.code: in {
  
    tarball = import ./make-tarball.nix;
  
  } // (mapTestOn ((packagesWithMetaPlatform pkgs) // rec {
  
  