anchor.diff:                  propagatedBuildInputs = filter (y : ! (y == null)) x.propagatedBuildInputs;
                   propagatedUserEnvPkgs = filter (y : ! (y == null)) x.propagatedUserEnvPkgs;
                   doCheck               = enableCheckPhase && x.doCheck;
  +                useCpphs              = enableCpphs && x.useCpphs;
                   hyperlinkSource       = enableHyperlinkSource && x.hyperlinkSource;
                   # Disable Darwin builds: <https://github.com/NixOS/nixpkgs/issues/2689>.
                   meta                  = let meta = x.meta or {};
  
positive.code:               export GHC_PACKAGE_PATH=$(${ghc.GHCPackages})
                test -n "$noHaddock" || ./Setup haddock --html --hoogle \
                    ${optionalString (stdenv.lib.versionOlder "6.12" ghc.version) "--ghc-options=-optP-P"} \
                    ${optionalString self.hyperlinkSource "--hyperlink-source"}
  
                eval "$postBuild"
              '';
  
negative.code:             # pass the '--enable-tests' flag to cabal in the configure stage
              # and run any regression test suites the package might have
              doCheck = enableCheckPhase;
  
              # force cpphs instead of the C compiler's preprocessor; sometimes
              # needed due to clang's wacky behavior
              useCpphs = false;
  
              # pass the '--hyperlink-source' flag to ./Setup haddock
              hyperlinkSource = enableHyperlinkSource;
  