name	nix-validation
description	Comprehensive Nix validation: treefmt-nix integration, statix/deadnix linting, flake checks, aytordev-specific patterns. Use when validating Nix code or setting up linting infrastructure.

Nix Validation & Linting

Name: nix-validation
Author: aytordev

Tool Overview

Tool	Purpose	Speed
`nix-instantiate --parse`	Syntax check only	Instant
`nixfmt`	Official formatter (RFC-style)	Fast
`statix`	Linter for anti-patterns	Fast
`deadnix`	Find unused code	Fast
`nix flake check`	Full evaluation + checks	Slow

treefmt-nix Integration

The recommended way to combine all tools:

# flake.nix
{
  inputs.treefmt-nix.url = "github:numtide/treefmt-nix";

  outputs = { self, nixpkgs, treefmt-nix, ... }:
    let
      system = "x86_64-linux";
      pkgs = nixpkgs.legacyPackages.''${system};
      treefmtEval = treefmt-nix.lib.evalModule pkgs {
        projectRootFile = "flake.nix";
        programs = {
          nixfmt.enable = true;  # or nixfmt-rfc-style
          deadnix.enable = true;
          statix.enable = true;
        };
      };
    in {
      formatter.''${system} = treefmtEval.config.build.wrapper;
      checks.''${system}.formatting = treefmtEval.config.build.check self;
    };
}

Statix Lints (Anti-Patterns)

Lint	Issue	Fix
`bool_comparison`	`x == true`	Just use `x`
`empty_let_in`	`let in expr`	Remove let-in
`eta_reduction`	`x: f x`	Just use `f`
`manual_inherit`	`x = x;`	Use `inherit x;`
`manual_inherit_from`	`x = a.x;`	Use `inherit (a) x;`
`legacy_let_syntax`	`let { x = 1; body = x; }`	Use `let x = 1; in x`
`unquoted_uri`	`https://...`	Quote the URI
`useless_parens`	`(expr)` when not needed	Remove parens

# Check for anti-patterns
statix check .

# Auto-fix what's possible
statix fix .

# Ignore specific lint
# Add to file: # statix: ignore manual_inherit

Deadnix (Unused Code)

# Find unused bindings
deadnix .

# Auto-remove unused code
deadnix -e .

# Check specific patterns
deadnix --no-lambda-arg .  # Keep unused lambda args
deadnix --no-lambda-pattern-names .  # Keep pattern names

Common False Positives:

self in flake outputs (hide with ...)
_ prefixed variables (intentionally unused)
Module arguments used in imports

aytordev-Specific Validation

# Validate module options follow namespace
nix eval .#nixosModules.default --apply 'm: builtins.attrNames (m {} { lib = (import <nixpkgs> {}).lib; config = {}; pkgs = {}; }).options.aytordev or {}'

# Check home-manager module
nix build .#homeConfigurations.khaneliman.activationPackage --dry-run

# Verify darwin configuration
nix build .#darwinConfigurations.khaneliman.system --dry-run

# Test specific host
nix build .#nixosConfigurations.khanelinux.config.system.build.toplevel --dry-run

Module Validation Patterns

# Check option types are correct
nix eval --expr '
  let
    pkgs = import <nixpkgs> {};
    module = import ./modules/mymodule.nix;
    result = pkgs.lib.evalModules {
      modules = [ module ];
    };
  in result.options
'

# Verify module doesn't have evaluation errors
nix eval --expr '
  let
    pkgs = import <nixpkgs> {};
    lib = pkgs.lib;
  in import ./path/to/module.nix { inherit lib pkgs; config = {}; }
'

Common Nix Errors & Fixes

Error	Cause	Fix
`syntax error, unexpected ';'`	Missing value before `;`	Check previous line for missing `=`
`undefined variable 'lib'`	Not in scope	Add `{ lib, ... }:` to function args
`infinite recursion encountered`	Self-reference in `rec`	Use `let` bindings or `self` pattern
`attribute 'x' missing`	Wrong path or typo	Check attr names, use `or default`
`cannot coerce set to string`	Using attrset as string	Use specific attr or `builtins.toJSON`
`function expects 1 arguments`	Missing argument	Check function signature
`called with unexpected argument`	Extra arg in call	Check function accepts arg

Flake Check Integration

# Add custom checks to flake
checks.''${system} = {
  # Formatting check
  formatting = treefmtEval.config.build.check self;

  # Module evaluation check
  module-eval = pkgs.runCommand "check-modules" {} '''
    ''${pkgs.nix}/bin/nix-instantiate --eval --strict \
      ''${self}/modules/test.nix
    touch $out
  ''';

  # Pre-commit hooks
  pre-commit = pre-commit-hooks.lib.''${system}.run {
    src = ./.;
    hooks = {
      nixfmt.enable = true;
      statix.enable = true;
      deadnix.enable = true;
    };
  };
};

Quick Validation Commands

# Fastest: syntax only
nix-instantiate --parse file.nix > /dev/null

# Fast: format + lint
nixfmt --check . && statix check . && deadnix .

# Project formatter (treefmt)
nix fmt

# Full check (slow but thorough)
nix flake check

# Git-aware (staged only)
git diff --cached --name-only | grep '\.nix$' | xargs -r nixfmt --check

Pre-Commit Hook (Nix)

# In devShell
devShells.default = pkgs.mkShell {
  packages = with pkgs; [ nixfmt statix deadnix ];
  shellHook = '''
    # Git pre-commit hook
    cat > .git/hooks/pre-commit << 'EOF'
    #!/bin/sh
    files=$(git diff --cached --name-only | grep '\.nix$')
    [ -z "$files" ] && exit 0
    echo "$files" | xargs nixfmt --check || exit 1
    echo "$files" | xargs statix check || exit 1
    echo "$files" | xargs deadnix || exit 1
    EOF
    chmod +x .git/hooks/pre-commit
  '

nix-validation

Install Skill

SKILL.md

Nix Validation & Linting

Tool Overview

treefmt-nix Integration

Statix Lints (Anti-Patterns)

Deadnix (Unused Code)

aytordev-Specific Validation

Module Validation Patterns

Common Nix Errors & Fixes

Flake Check Integration

Quick Validation Commands

Pre-Commit Hook (Nix)