+@functools.lru_cache
+def _experimental_flag_needed(v: Verification) -> bool:
+ v.status('Checking Nix version')
+ process = subprocess.run(['nix', '--help'], stdout=subprocess.PIPE)
+ v.result(process.returncode == 0)
+ return b'--experimental-features' in process.stdout
+
+
+def _nix_command(v: Verification) -> List[str]:
+ return ['nix', '--experimental-features',
+ 'nix-command'] if _experimental_flag_needed(v) else ['nix']
+
+