Nix-bisect -- Bisect Nix Builds

timokau · March 9, 2020, 5:20pm

Check out this deliciously ugly hack I cooked up to bisect a whole nixos+home-manager system for #80936:

timokau/nix-bisect/blob/8e8e8c593e268a8cad2ab1016c7a705136151f6b/doc/examples/system.py#L17


      
          from subprocess import Popen, PIPE
          from multiprocessing import Process
          from pathlib import Path
          
          
from nix_bisect import nix, test_util, git_bisect
          
          

          
def _main():
              process = Popen("bash", stdin=PIPE, stdout=PIPE, encoding="UTF-8")
          
          
    # Hack to "instantiate" the home-manager system configuration.
              with tempfile.TemporaryDirectory() as tmpdirname:
                  # Monkey-patch "nix-build" by creating a mock nix-build script in a
                  # temporary directory and then prepending that directory to PATH.
                  # The goal here is to just print the instantiation result but not
                  # actually do the building.
                  nix_build_path = Path(tmpdirname).joinpath("nix-build")
                  with open(nix_build_path, "w+") as nix_build_mock:
                      nix_build_mock.write(
                          """
                          #!/usr/bin/env bash

It involves monkey-patching nix-build in the home-manager switch script to print out the instantiation result instead.