How to install nixfmt on macOS or without NixOS?

Nixfmt is distributed through Nix packages. On macOS, install Nix first via the official installer, then use nix-env or Home Manager. For non-Nix systems, you might need to build from source or use a container, but the README focuses on Nix-based methods.

nixfmt vs alejandra which should I use?

Nixfmt is the official formatter adhering to the Nix community standard, while alejandra is a third-party tool with more aggressive, opinionated formatting. Choose nixfmt for compliance with official standards, or alejandra if you prefer stricter, automated style fixes.

How to set up nixfmt with pre-commit hooks in my repo?

Add nixfmt to your .pre-commit-config.yaml file with the repo URL and hook ID as shown in the README. Then run pre-commit install to enable it. This automates formatting checks before each commit, ensuring consistency.

Can nixfmt format only specific lines or exclude parts of a file?

No, nixfmt formats entire Nix files according to the standard without options for partial formatting. If you need exclusions, you may need to manage formatting manually or use other tools in combination.

Does nixfmt work in CI pipelines like GitHub Actions?

Yes, you can integrate nixfmt in CI by installing Nix and nixfmt in the pipeline, then running it on files. Combine it with treefmt or pre-commit for batch processing. The README doesn't specify CI examples, but it's feasible with Nix tooling.

What are the common formatting rules nixfmt enforces?

Nixfmt applies the artistic formatting rules defined in standard.md, such as consistent indentation, line breaks, and spacing. Refer to the standard.md file in the repository for detailed specifications on Nix code style.

Open-Awesome

nixfmt

MPL-2.0Haskellv1.4.0

The official formatter for Nix language code, enforcing a standard artistic formatting style.

GitHub

1.6k stars75 forks0 contributors

What is nixfmt?

Nixfmt is the official code formatter for the Nix language. It automatically formats Nix code to comply with a standard artistic style defined by the Nix community, ensuring consistency across projects. It solves the problem of inconsistent formatting in Nix codebases, making code more readable and maintainable.

Target Audience

Nix developers and teams working on Nix projects who want to enforce a consistent code style automatically. It's particularly useful for collaborative environments where multiple contributors edit Nix files.

Value Proposition

Developers choose Nixfmt because it's the officially maintained formatter for Nix, providing a single source of truth for formatting rules. It integrates seamlessly with popular editors, Git hooks, and project tooling, reducing configuration overhead and ensuring adherence to community standards.

Overview

The official formatter for Nix code

Use Cases

Best For

Enforcing consistent code style across Nix projects
Automating formatting checks in CI/CD pipelines
Integrating formatting into editor workflows for Nix development
Setting up pre-commit hooks for Nix repositories
Resolving formatting-related merge conflicts in Git
Standardizing Nix code in large, collaborative teams

Not Ideal For

Projects requiring batch formatting of multiple Nix files without additional tooling like treefmt
Teams with established, custom formatting rules that conflict with the official Nix community standard
Environments without the Nix package manager installed, as installation and execution depend on Nix

Pros & Cons

Pros

Official Standard Adherence

Maintained by the Nix formatting team, it enforces the community-defined artistic formatting from standard.md, eliminating style debates in collaborative projects.

Seamless Editor Integration

Works with popular editors like neovim (via nixd, nil, none-ls) and VSCode through extensions, making it easy to incorporate into daily workflows.

Advanced Git Tooling

Includes a --mergetool mode for resolving formatting-related conflicts and supports pre-commit hooks via git-hooks.nix or direct configuration, automating checks.

Nix Ecosystem Integration

Easily installable via NixOS, Home Manager, and declarative shells, and integrates with project tools like treefmt-nix and nix fmt for flakes.

Cons

Single-File Limitation

The core tool can only process one file at a time, requiring external wrappers like treefmt for project-wide formatting, as noted in the README.

Nix Dependency Barrier

Installation and use are tied to the Nix package manager, which can be a hurdle for developers not already in the Nix ecosystem or using other OSes.

No Formatting Customization

Formats strictly to the community standard with no built-in options to adjust rules, which may not suit teams preferring different styles.

Frequently Asked Questions

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