nix/SIMPLE_HOOKS.md

Git Hooks - Simple Declarative Setup

Concept

Hooks are defined in Nix (flake.nix) and installed by running nix flake check once.

No systemd services, no activation scripts, no complexity.

How It Works

1. Hooks Defined in Nix

flake.nix:

checks.${system}.pre-commit-check = git-hooks.lib.${system}.run {
  src = ./.;
  hooks = {
    nixfmt.enable = true;
    statix.enable = true;
    deadnix.enable = true;
  };
};

2. Installation

Run once on each host:

nix flake check

This installs the hooks and creates .git/hooks/pre-commit.

3. Automatic

• ✅ Hooks run on every git commit
• ✅ CI runs nix flake check automatically
• ✅ Hooks checked on every push/PR

Usage

Install Hooks (One-Time Per Host)

# From the flake directory
nix flake check

# You should see hooks installing

Verify Installation

ls -la .git/hooks/

Should show pre-commit (and potentially other hooks).

Test Hooks

# Create a file with bad formatting
echo "broken { }" > test.nix

# Try to commit (should fail)
git add test.nix
git commit -m "test"

# Clean up
rm test.nix

What's Declarative

Aspect	Status
Hook definitions	✅ Yes - in flake.nix
Hook installation	✅ Yes - via nix flake check
CI integration	✅ Yes - via nix flake check in workflows
Local git hooks	✅ Yes - run automatically on commit
No systemd services	✅ Removed - too complex
No activation scripts	✅ Removed - unnecessary
One-time setup	✅ Yes - run nix flake check once per host

Files

File	Status
flake.nix	✅ Hook definitions
.github/workflows/flake-check.yaml	✅ CI uses nix flake check
.editorconfig	✅ Code style
modules/git-hooks/default.nix	❌ DELETED - Not needed
hosts/*/default.nix	✅ CLEANED - Removed git-hooks

Next Steps

1. Test locally:

   nix flake check
   ls -la .git/hooks/
   echo "broken { }" > test.nix
   git add test.nix
   git commit -m "test"  # Should fail
   rm test.nix
   

2. Commit changes:

   git add .
   git commit -m "Simplify: Git hooks via nix flake check (no systemd, no activation)"
   git push
   

3. Run nix flake check on each host when you next rebuild

This Is The Right Approach Because

Issue	Overcomplicated Solution	Simple Solution
Declarative	❌ Systemd service is separate from Nix	✅ Hooks in flake.nix, install via nix flake check
Simple	❌ Multiple layers (activation, systemd)	✅ One command: nix flake check
Idempotent	❌ Runs on every rebuild	✅ Idempotent - run once per host
Reproducible	❌ Depends on systemd state	✅ Pure Nix

Summary

The simplest declarative approach:

1. Define hooks in flake.nix ✅ Already done
2. Run nix flake check once per host ✅ To do
3. That's it! Hooks work automatically ✅ Declarative

No systemd services. No activation scripts. No complexity.