flake-pin

A CLI tool for automatically pinning/updating Nix flake inputs to their latest GitHub commits.

🚧 Status: In Development

This tool is currently under development and not yet functional.

What it does

flake-pin takes a flake input name and updates it to the latest commit from GitHub:

• Reads your flake.lock to find the current state of the input
• Fetches the latest commit hash from the GitHub API
• Updates your flake.nix to pin the input to the latest commit (first 7 characters)
• Adds or updates a comment with the commit date (UTC) in ISO-8601 format

Although packages can be pinned individually by using the flake lock API, explicit pinning in the flake file:

• pins are prominently visible near the top of the flake file, and
• enables use of flake update with granular control of what is pinned.

Features

• 🛟 Type-safe parsing and modification of Nix files
• 🚀 Uses GitHub API for reliable commit information
• 📝 Automatic date comments

Example

Before (in flake.nix):

emacs-overlay.url = "github:nix-community/emacs-overlay";

Update the "emacs-overlay" input to latest commit

flake-pin --input emacs-overlay /path/to/your/flake

After:

emacs-overlay.url = "github:nix-community/emacs-overlay/8dc6642"; # 2025-06-18

Installation

With Nix (recommended)

Add to your flake inputs, or run directly.

Run directly

nix run github:what-the-functor/flake-pin -- --input emacs-overlay /path/to/flake

With Cabal

git clone https://github.com/what-the-functor/flake-pin
pushd flake-pin
cabal install

Usage

flake-pin --input <input-name> <flake-path>

• input-name: The name of the flake input to update (e.g., "nixpkgs", "emacs-overlay")
• flake-path: Path to the directory containing the flake.nix file

Development

With Nix

git clone https://github.com/what-the-functor/flake-pin
pushd flake-pin
nix develop
cabal build
cabal test

Without Nix

Requirements:

• GHC 9 (tested with 9.8.4)
• Cabal
• Fourmolu

cabal build
cabal test

Contributing

This project uses TDD with property-based testing. Pull requests should include tests for new functionality. Format with Fourmolu

License

MIT