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] --exclude <EXCLUDES>... Files to exclude from analysis -V, --version Print version

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

The --exclude parameter accepts multiple paths. Separate them with -- to pass [FILE_PATHS]....

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 -l/--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 -L/--no-lambda-pattern-names in this case.