anchor.diff:              api/xml/"$(basename "$xml")"
           done
   
  -        tar -Jcvf opengl-headers-${version}.tar.xz api/
  +        tar -Jcvf opengl-headers-${date}.tar.xz api/
         '';
   
         installPhase = ''
  -        install -D -m644 -v 'opengl-headers-${version}.tar.xz' \
  -          "$out/opengl-headers-${version}.tar.xz"
  +        install -D -m644 -v 'opengl-headers-${date}.tar.xz' \
  +          "$out/opengl-headers-${date}.tar.xz"
         '';
       };
     };
  
positive.code: # TODO: build release tarballs, repo vendors pdfs
  
  let
    version = "2019-03-01";
  in
  stdenv.mkDerivation rec {
    name = "opengl-headers-${version}";
  
    src = fetchurl {
      name = "opengl-headers-${version}.tar.xz";
      multihash = "QmZdRTzsSxGWTSzmChywUgo6drKFoho8qDh4FagumAM3eS";
      sha256 = "7cfa0ed4091b4d04c33b1be3c30361f9613b7301744f0b4b6397b923d82295d0";
    };
  
    configurePhase = ":";
  
negative.code:       postPatch = ''
          sed -i xml/genglvnd.py \
            -e 's,drafts/,,'
  
          # Fix impure date in headers
          grep -q "time.strftime('%Y%m%d')" xml/genheaders.py
          sed -i xml/genheaders.py \
            -e "s,time.strftime('%Y%m%d'),'${lib.replaceStrings ["-"] [""] date}',"
        '';
  
        configurePhase = ":";
  