anchor.diff:                  f0 self super
                 else x;
           in
  -          makeDerivationExtensible mkDerivationSimple (self: attrs // f self attrs))
  +          makeDerivationExtensible (self: attrs // f self attrs))
         attrs;
   
     mkDerivationSimple = overrideAttrs:
  
positive.code: in
    fnOrAttrs:
      if builtins.isFunction fnOrAttrs
      then makeDerivationExtensible mkDerivationSimple fnOrAttrs
      else makeDerivationExtensibleConst mkDerivationSimple fnOrAttrs
  
negative.code:                     f0 self super
                    else x;
              in
                makeDerivationExtensible
                  (self: let super = rattrs self; in super // f self super))
            args;
      in finalPackage;
  
    # makeDerivationExtensibleConst == makeDerivationExtensible (_: attrs),
    # but pre-evaluated for a slight improvement in performance.
    makeDerivationExtensibleConst = attrs:
      mkDerivationSimple
        (f0:
          let
  