mynix

#!/usr/bin/env python3
import argparse
import os
import shutil
import subprocess
import sys

description = '''
Script to pin nix, nixpkgs etc versions for reproducibility.

Simply write `./mynix` in front of any nix-related command.

See 'pinned-tools.nix' for which tools are pinned.
'''

parser = argparse.ArgumentParser(description=description)
parser.add_argument('rest', nargs=argparse.REMAINDER)
args = parser.parse_args()

env = dict(
  os.environ,
  NIX_PATH='nix-channel', # our nixpkgs submodule is a subdir in here
  # Other environment vars we want to always set for this project:
  NIXOPS_STATE='localstate.nixops',
)

if shutil.which('nix-build') is None:
  sys.exit("nix is not available, please install it first")

# Get pinned `nix` executable
fixed_nix_bin_path = os.path.join(subprocess.check_output(
    ['nix-build', '-E', 'with (import <nixpkgs> {}); pkgs.nix', '--no-link'],
    env=env,
    universal_newlines=True,
  ).strip(), 'bin')

# Get pinned tools /bin path
pinned_tools_bin_path = os.path.join(subprocess.check_output(
    [fixed_nix_bin_path + '/nix-build', 'pinned-tools.nix', '-o', 'pinned-tools'],
    env=env,
    universal_newlines=True,
  ).strip(), 'bin')

# Add our pinned tools to PATH
env['PATH'] = pinned_tools_bin_path + os.pathsep + env['PATH']

# Run command and exit
if args.rest == []:
  parser.print_help()
else:
  sys.exit(subprocess.call(args.rest, env=env))