Cleaning the derivation source directory during development #nix

derivation_source_directory_clean.md

Cleaning the derivation source directory during development

During development it's really important to apply a cleaning filter to the src attribute before you run a nix-build. If you don't do this, your entire directory contents will be copied into the /nix/store as a content addressed dependency. This includes large files, secret files and other files that is not use for building the package!

The most basic filter is simply:

src = lib.cleanSource ./.;

It is defined here: https://github.com/NixOS/nixpkgs/blob/master/lib/sources.nix

This automatically filters out:

• .git and other version control repositories.
• Vim meta files
• .o and .so files
• ./result and ./result-* symlinks

However you may have other files that you want to also filter out. For example a .env file or temporary data directories.

To do this, you need to use a more sophisticated filter:

src = lib.cleanSourceWith {
  filter = (path: type:
    ! (builtins.any
        (r: (builtins.match r (builtins.baseNameOf path)) != null)
        [
          "\.env"
          "tmp"
          "logs"
          "data"
        ])
  );
  src = lib.cleanSource ./.;
};

The above filter filters only at the project root. It asks to match a list of regular expressions against the basename of the paths at the project root. In this case, we are filtering out .env, tmp, logs and data in addition to the default filters in lib.cleanSource.

Note that in the case you are using a shell.nix, you should use:

src = null;

Because you are doing development in the project directory, so you don't want to copy anything to the /nix/store except of course for your dependencies.

There is also some work on extending filterSource to support ignore paths similar to .gitignore: NixOS/nix#885