anchor.diff:  
     src = fetchurl {
       urls = [
  +      "https://mesa.freedesktop.org/archive/mesa-${version}.tar.xz"
         "ftp://ftp.freedesktop.org/pub/mesa/mesa-${version}.tar.xz"
         "ftp://ftp.freedesktop.org/pub/mesa/${version}/mesa-${version}.tar.xz"
         "ftp://ftp.freedesktop.org/pub/mesa/older-versions/${branch}.x/${version}/mesa-${version}.tar.xz"
  -      "https://mesa.freedesktop.org/archive/mesa-${version}.tar.xz"
       ];
  -    sha256 = "0vz8k07d23qdwy67fnna9y0ynnni0m8lgswcmdm60l4mcv5z2m5a";
  +    sha256 = "0y517qpdg6v6dsdgzb365p03m30511sbyh8pq0mcvhvjwy7javpy";
     };
   
     prePatch = "patchShebangs .";
  
positive.code: with stdenv.lib;
  
  let
    version = "20.0.2";
    branch  = versions.major version;
  in
  
  
negative.code:     changelog = "https://www.mesa3d.org/relnotes/${version}.html";
      license = licenses.mit; # X11 variant, in most files
      platforms = platforms.mesaPlatforms;
      maintainers = with maintainers; [ primeos vcunat ]; # Help is welcome :)
    };
  }
  