anchor.diff:      unpackPhase ? "",
       configurePhase ? "",
       buildPhase ? "",
  +    preInstall ? "",
  +    postInstall ? "",
       path ? (builtins.parseDrvName name).name,
       addonInfo ? null,
       ...
  
positive.code:         if [ -n "$addonInfo" ]; then
            echo "$addonInfo" > $target/addon-info.json
          fi
        '';
      }));
  
  
negative.code:     addRtp "${rtpPath}/${path}" (stdenv.mkDerivation (a // {
        name = namePrefix + name;
  
        inherit unpackPhase configurePhase buildPhase addonInfo preInstall postInstall;
  
        installPhase = ''
          runHook preInstall
  
          target=$out/${rtpPath}/${path}
          mkdir -p $out/${rtpPath}
          cp -r . $target
  