anchor.diff:                    then pkgs.lib.cleanSourceWith { inherit src filter; }
                   else src;
           };
  -      in overrideCabal (callPackageKeepDeriver expr args) (orig: {
  +      in overrideCabal (orig: {
              inherit src;
  -         });
  +         }) (callPackageKeepDeriver expr args);
   
       callCabal2nix = name: src: args: self.callCabal2nixWithOptions name src "" args;
   
  
positive.code:         # cabal2nixDeriver field.
          cabal2nixDeriver = src;
        };
      });
  
  in package-set { inherit pkgs lib callPackage; } self // {
  
  
negative.code:   # (requiring it to be frequently rebuilt), which can be an
    # annoyance.
    callPackageKeepDeriver = src: args:
      overrideCabal (orig: {
        preConfigure = ''
          # Generated from ${src}
          ${orig.preConfigure or ""}
  