deadnix

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

Usage with Github Actions

Usage with Nix Flakes

Help

```console $ 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 to use [default: human-readable] [possible values: human-readable, json] --exclude ... Files to exclude from analysis -V, --version Print version ```

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

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

Scan for unused code

console $ 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!

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

Usage with pre-commit

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

yaml 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.

Skipping reports for certain declarations

As of 1.1.0 deadnix supports the following pragma to skip check of bindings in the following line:

```nix

deadnix: skip

```

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.