deadnix

Scan .nix files for dead code (unused variable bindings).

Usage with Github Actions

See deadnix-action

Usage with Nix Flakes

Help

$ nix run github:astro/deadnix -- --help
Find dead code in .nix files

Usage: deadnix [OPTIONS] [FILE_PATHS]...

Arguments:
  [FILE_PATHS]...  .nix files, or directories with .nix files inside [default: .]

Options:
  -l, --no-lambda-arg
          Don't check lambda parameter arguments
  -L, --no-lambda-pattern-names
          Don't check lambda attrset pattern names (don't break nixpkgs callPackage)
  -_, --no-underscore
          Don't check any bindings that start with a _
  -q, --quiet
          Don't print dead code report
  -e, --edit
          Remove unused code and write to source file
  -h, --hidden
          Recurse into hidden subdirectories and process hidden .*.nix files
      --help
          
  -f, --fail
          Exit with 1 if unused code has been found
  -o, --output-format <OUTPUT_FORMAT>
          Output format to use [default: human-readable] [possible values: human-readable, json]
  -V, --version
          Print version information

Reports contain ANSI color escape codes unless the $NO_COLOR environment variable is set.

Scan for unused code

$ nix run github:astro/deadnix example.nix                                               
Warning: Unused declarations were found.
    ╭─[example.nix:1:1]
  1 │unusedArgs@{ unusedArg, usedArg, ... }:
    ·     │           ╰───── Unused lambda pattern: unusedArg
    ·     ╰───────────────── Unused lambda pattern: unusedArgs
  3 │  inherit (builtins) unused_inherit;
    ·                            ╰─────── Unused let binding: unused_inherit
  5 │  unused = "fnord";
    ·     ╰─── Unused let binding: unused
 10 │  shadowed = 42;
    ·      ╰──── Unused let binding: shadowed
 11 │  _unused = unused: false;
    ·     │         ╰─── Unused lambda argument: unused
    ·     ╰───────────── Unused let binding: _unused
 13 │  x = { unusedArg2, x ? args.y, ... }@args: used1 + x;
    ·             ╰───── Unused lambda pattern: unusedArg2

Remove unused code automatically

Do commit your changes into version control before!

$ nix run github:astro/deadnix -- -eq test.nix

Usage with pre-commit

Add the following to your project's .pre-commit-config.yaml:

repos:
  - repo: https://github.com/astro/deadnix
    rev: ID # frozen: VERSION
    hooks:
      - id: deadnix
        #args: [--edit] # Uncomment to automatically modify files
        stages: [commit]

Replace ID and VERSION above with the relevant version tag and commit ID for reference, for example:

rev: da39a3ee5e6b4b0d3255bfef95601890afd80709  # frozen: v1.2.3

Behavior

Renaming of all unused to lambda args to start with _

If you disfavor marking them as unused, use option --no-lambda-arg.

nixpkgs callPackages with multiple imports

callPackages guesses the packages to inject by the names of a packages' lambda attrset pattern names. Some packages alias these with @args to pass them to another import ...nix args.

As the used args are only named in the imported file they will be recognized as dead in the package source file that is imported by callPackage, rendering it unable to guess the dependencies to call the packages with.

Use option --no-lambda-pattern-names in this case.

What if the produced reports are wrong?

Please open an issue. Do not forget to include the .nix code that produces incorrect results.

Commercial Support

The author can be hired to implement the features that you wish, or to integrate this tool into your toolchain.