test.nix

{ pkgs ? import <nixpkgs-unstable> {} }:
let
  buildInstrumentedAdapter = stdenv:
  let
    flags = "-fprofile-instr-generate -fcoverage-mapping";
  in
  stdenv //
  { mkDerivation = args: stdenv.mkDerivation (args // {
      NIX_CFLAGS_COMPILE = toString (args.NIX_CFLAGS_COMPILE or "") + " " + flags;
      NIX_LDFLAGS_COMPILE = toString (args.NIX_CFLAGS_COMPILE or "") + " " + flags;
    });
  };
  enableInstrumented = pkg: 
    let
      clangStdenv = pkgs.overrideCC pkgs.llvmPackages_11.stdenv pkgs.clang;
    in
    pkg.override {
      stdenv = buildInstrumentedAdapter clangStdenv;
    };
in
enableInstrumented pkgs.xlibs.libX11