nix-validation

Nix Validation & Linting

Tool Overview

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)

# 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

khanelinix-Specific Validation

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

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
  '