anchor.diff:  stdenv.mkDerivation rec {
     name = "opencv-${version}";
     inherit version src;
  -
  -  patches = [
  -    # Fix for: https://github.com/opencv/opencv/issues/10474
  -    (fetchpatch {
  -      url = "https://github.com/opencv/opencv/commit/ea5a3e557f93844fdb5e54e3e8acfc5f61c6fd9f.patch";
  -      sha256 = "1w7jmqlrx73ydh9jjsnnic5xz8r04kxbjpzkcfyb91v3az9132r1";
  -    })
  -  ];
   
     postUnpack = lib.optionalString buildContrib ''
       cp --no-preserve=mode -r "${contribSrc}/modules" "$NIX_BUILD_TOP/opencv_contrib"
  
positive.code: }:
  
  let
    version = "3.4.0";
  
    src = fetchFromGitHub {
      owner  = "opencv";
      repo   = "opencv";
      rev    = version;
      sha256 = "1nc14kvsjwaisv7d1r6f0hn7na9zr2cm2zh3hd3r9qwm3g78xnac";
    };
  
    contribSrc = fetchFromGitHub {
      owner  = "opencv";
      repo   = "opencv_contrib";
      rev    = version;
      sha256 = "1cxw7nra3f1hng057c6hi1ynsyqdazd69irjdgn8xjg6q9h76br0";
    };
  
    # Contrib must be built in order to enable Tesseract support:
  
negative.code:     "-DOPENCV_ENABLE_NONFREE=${printEnabled enableUnfree}"
      "-DBUILD_TESTS=OFF"
      "-DBUILD_PERF_TESTS=OFF"
      "-DBUILD_DOCS=${printEnabled enableDocs}"
      (opencvFlag "IPP" enableIpp)
      (opencvFlag "TIFF" enableTIFF)
      (opencvFlag "JASPER" enableJPEG2K)
  