nix/doc/manual/src/contributing/hacking.md

Hacking

This section provides some notes on how to hack on Nix. To get the latest version of Nix from GitHub:

$ git clone https://github.com/NixOS/nix.git
$ cd nix

To build Nix for the current operating system/architecture use

$ nix-build

or if you have a flake-enabled nix:

$ nix build

This will build defaultPackage attribute defined in the flake.nix file. To build for other platforms add one of the following suffixes to it: aarch64-linux, i686-linux, x86_64-darwin, x86_64-linux. i.e.

$ nix-build -A defaultPackage.x86_64-linux

To build all dependencies and start a shell in which all environment variables are set up so that those dependencies can be found:

$ nix-shell

or if you have a flake-enabled nix:

$ nix develop

To get a shell with a different compilation environment (e.g. stdenv, gccStdenv, clangStdenv, clang11Stdenv):

$ nix-shell -A devShells.x86_64-linux.clang11StdenvPackages

or if you have a flake-enabled nix:

$ nix develop .#clang11StdenvPackages

To build Nix itself in this shell:

[nix-shell]$ ./bootstrap.sh
[nix-shell]$ ./configure $configureFlags --prefix=$(pwd)/outputs/out
[nix-shell]$ make -j $NIX_BUILD_CORES

To install it in $(pwd)/outputs and test it:

[nix-shell]$ make install
[nix-shell]$ make installcheck -j $NIX_BUILD_CORES
[nix-shell]$ ./outputs/out/bin/nix --version
nix (Nix) 3.0

If you have a flakes-enabled Nix you can replace:

$ nix-shell

by:

$ nix develop

Testing Nix

Nix comes with three different flavors of tests: unit, functional and integration.

Unit-tests

The unit-tests for each Nix library (libexpr, libstore, etc..) are defined under src/{library_name}/tests using the googletest framework.

You can run the whole testsuite with make check, or the tests for a specific component with make libfoo-tests_RUN. Finer-grained filtering is also possible using the --gtest_filter command-line option.

Functional tests

The functional tests reside under the tests directory and are listed in tests/local.mk. The whole testsuite can be run with make install && make installcheck. Individual tests can be run with make tests/{testName}.sh.test.

Integration tests

The integration tests are defined in the Nix flake under the hydraJobs.tests attribute. These tests include everything that needs to interact with external services or run Nix in a non-trivial distributed setup. Because these tests are expensive and require more than what the standard github-actions setup provides, they only run on the master branch (on https://hydra.nixos.org/jobset/nix/master).

You can run them manually with nix build .#hydraJobs.tests.{testName} or nix-build -A hydraJobs.tests.{testName}

Testing the install scripts

Testing the install scripts has traditionally been tedious, but you can now do this much more easily via the GitHub Actions CI runs (at least for platforms that Github Actions supports).

If you've already pushed to a fork of Nix on GitHub before, you may have noticed that the CI workflows in your fork list skipped installer and installer_test jobs. Once your Nix fork is set up correctly, pushing to it will also run these jobs.

• The installer job will generate installers for these platforms:

  • x86_64-linux
  • armv6l-linux
  • armv7l-linux
  • x86_64-darwin.

  While this installer is in your Cachix cache, you can use it for manual testing on any of these platforms.

• the installer_test job will try to use this installer and run a trivial Nix command on ubuntu-latest and macos-latest.

One-time setup

1. Have a GitHub account with a fork of the Nix repo.
2. At cachix.org:
   • Create or log in to an account.
   • Create a Cachix cache using the format <github-username>-nix-install-tests.
   • Navigate to the new cache > Settings > Auth Tokens.
   • Generate a new cachix auth token and copy the generated value.
3. At github.com:
   • Navigate to your Nix fork > Settings > Secrets > Actions > New repository secret.
   • Name the secret CACHIX_AUTH_TOKEN
   • Paste the copied value of the Cachix cache auth token.

Using the CI-generated installer for manual testing

After the CI run completes, you can check the output to extract the installer url:

1. Click into the detailed view of the CI run.

2. Click into any installer_test run (the URL you're here to extract will be the same in all of them).

3. Click into the Run cachix/install-nix-action@v... step and click the detail triangle next to the first log line (it will also be Run cachix/install-nix-action@v...)

4. Copy the value of install_url

5. To generate an install command, plug this install_url and your GitHub username into this template:

   sh <(curl -L <install_url>) --tarball-url-prefix https://<github-username>-nix-install-tests.cachix.org/serve