anchor.diff:    ] ++ lib.optionals introspectionSupport [
       gobject-introspection
       vala
  +  ] ++ lib.optionals stdenv.isDarwin [
  +    fixDarwinDylibNames
     ];
     installCheckInputs = [
       # running libical-glib tests
  
positive.code: , libical
  , python3
  , tzdata
  , introspectionSupport ? stdenv.buildPlatform == stdenv.hostPlatform
  , gobject-introspection ? null
  , vala ? null
  }:
  
  assert introspectionSupport -> gobject-introspection != null && vala != null;
  
  stdenv.mkDerivation rec {
    pname = "libical";
  
negative.code:   # LD_LIBRARY_PATH and GI_TYPELIB_PATH variables
    doInstallCheck = true;
    enableParallelChecking = false;
    preInstallCheck = if stdenv.isDarwin then ''
      for testexe in $(find ./src/test -maxdepth 1 -type f -executable); do
        for lib in $(cd lib && ls *.3.dylib); do
          install_name_tool -change $lib $out/lib/$lib $testexe
        done
      done
    '' else null;
    installCheckPhase = ''
      runHook preInstallCheck
  
  