anchor.diff:      "--disable-zsh-mem-debug"
       "--disable-zsh-mem-warning"
       "--disable-zsh-secure-free"
  +    "--disable-zsh-heap-debug"
       "--disable-zsh-valgrind"
       "--disable-zsh-hash-debug"
       # Tests fail with stack allocation enabled >=5.2
  
positive.code:     boolWt
      optionals;
  
    version = "5.3.1";
  
    documentation = fetchurl {
      url = "mirror://sourceforge/zsh/zsh-doc/${version}/"
        + "zsh-${version}-doc.tar.xz";
      hashOutput = false;
      sha256 = "d51762fcb5699c332da8a4e404cb9eb8d5de8fa4e0235a08bcf252c915bda6ed";
    };
  in
  stdenv.mkDerivation rec {
  
negative.code:     "--disable-ansi2knr"
      "--enable-function-subdirs"
      "--enable-maildir-support"
      "--enable-readnullcmd=${less}/bin/less"
      "--${boolEn (pcre != null)}-pcre"
      "--${boolEn (libcap != null)}-cap"
      "--${boolEn (gdbm != null)}-gdbm"
      "--enable-largefile"
      "--enable-multibyte"
      "--enable-unicode9"
      # TODO: musl libc support
      "--disable-libc-musl"
      "--enable-dynamic-nss"
  