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

USAGE:
    deadnix [OPTIONS] [FILE_PATHS]...

ARGS:
    <FILE_PATHS>...    .nix files, or directories with .nix files inside

OPTIONS:
    -_, --no-underscore              Don't check any bindings that start with a _
    -e, --edit                       Remove unused code and write to source file
    -f, --fail                       Exit with 1 if unused code has been found
    -h, --hidden                     Recurse into hidden subdirectories and process hidden .*.nix
                                     files
        --help                       Print help information
    -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)
    -q, --quiet                      Don't print dead code report
    -V, --version                    Print version information

Scan for unused code

$ nix run github:astro/deadnix test.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

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.