anchor.diff:      # work fine, and I'm not sure how to write the condition.
       ++ stdenv.lib.optional stdenv.hostPlatform.isWindows ./mcfgthreads-no-pthread.patch;
   
  -  postPatch =
  -  # Patch shebangs for playTests
  -  ''
  -    patchShebangs programs/zstdgrep
  -  '' + stdenv.lib.optionalString (!static) ''
  +  postPatch = stdenv.lib.optionalString (!static) ''
       substituteInPlace build/cmake/CMakeLists.txt \
         --replace 'message(SEND_ERROR "You need to build static library to build tests")' ""
       substituteInPlace build/cmake/tests/CMakeLists.txt \
  
positive.code:   doCheck = true;
    checkPhase = ''
      runHook preCheck
      ctest -R playTests # The only relatively fast test.
      runHook postCheck
    '';
  
negative.code: { stdenv, fetchFromGitHub, fetchpatch, cmake, bash, gnugrep
  , fixDarwinDylibNames
  , file
  , legacySupport ? false
  