How to set up treefmt-nix with Nix flakes?

Add treefmt-nix as an input in your flake.nix, define a treefmt.nix configuration file enabling formatters, and use nix fmt to run formatting. The README provides step-by-step examples for integration.

treefmt-nix vs pre-commit hooks for formatting?

treefmt-nix centralizes formatting with Nix for reproducibility and seamless dev environment integration, while pre-commit hooks are lighter but require separate tool management and may lack Nix's consistency guarantees.

Can I use treefmt-nix without NixOS?

Yes, treefmt-nix works with any Nix installation, including on non-NixOS Linux, macOS, or Windows with WSL, but it requires Nix to be properly set up and maintained.

How to add a custom formatter not in the supported list?

Define a custom formatter in the settings using shell commands, as shown in the README with the yq-go example for JSON formatting. This allows flexibility for unsupported tools.

Does treefmt-nix support JavaScript formatting with prettier?

Yes, prettier is included in the supported programs list, and you can enable it via programs.prettier.enable in your Nix configuration, with options to customize includes and excludes.

What's the performance overhead of treefmt-nix?

Minimal overhead during runs as it wraps existing formatters, but initial Nix builds might take time due to derivation evaluations. Subsequent executions are fast and cached.

How to run treefmt-nix in CI for formatting checks?

Use nix flake check in your CI pipeline, which validates formatting based on the flake configuration. This ensures code meets standards before merging, as documented in the CI/CD section.

Open-Awesome

treefmt-nix

MITNix

A Nix library to configure and run treefmt, enabling multi-language code formatting with a single command.

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What is treefmt-nix?

treefmt-nix is a Nix library that configures and runs treefmt, a tool for formatting code across multiple programming languages with a single command. It allows developers to manage formatter dependencies and settings entirely within Nix, providing a reproducible and integrated formatting workflow. The project solves the problem of managing disparate formatter tools and configurations by centralizing them in Nix expressions.

Target Audience

Nix users and developers working in polyglot codebases who want a unified, declarative approach to code formatting. It is particularly useful for teams using Nix development environments or flakes.

Value Proposition

Developers choose treefmt-nix because it deeply integrates with Nix, offering a declarative configuration, automatic formatter installation, and seamless compatibility with Nix development shells and CI/CD pipelines. Its extensive library of pre-configured formatters saves time and ensures consistency.

Overview

treefmt nix configuration

Use Cases

Best For

Formatting multi-language projects with a single command
Integrating code formatting into Nix development environments
Ensuring consistent formatting across CI/CD pipelines
Managing formatter dependencies declaratively with Nix
Adding custom formatters not covered by standard tools
Using Nix flakes for project formatting and validation

Not Ideal For

Teams not using Nix in their development workflow
Projects requiring quick, ad-hoc formatting without Nix setup overhead
Environments where Nix is unsupported, such as some Windows setups without WSL

Pros & Cons

Pros

Deep Nix Integration

Formatters, dependencies, and configurations are managed declaratively in Nix, eliminating separate TOML files and ensuring reproducible builds across environments.

Extensive Formatter Library

Includes over 100 community-maintained formatter configurations for languages like Python, Rust, and Go, reducing setup time and ensuring consistency.

Seamless Dev Environment

Automatically installs and configures formatters, integrating with Nix development shells and flakes for easy setup in polyglot projects.

CI/CD Ready

Works with nix flake check to validate formatting in continuous integration, providing a built-in way to enforce code standards without extra tooling.

Cons

Nix Dependency Lock-in

Requires a Nix environment to function, making it unsuitable for teams not already invested in Nix or in environments where Nix is difficult to deploy.

Configuration Complexity

Setting up involves writing Nix expressions, which can be steep for developers unfamiliar with Nix, and overkill for simple formatting needs.

Limited Formatter Updates

While many formatters are supported, adding new or niche formatters requires manual PRs or custom definitions, and updates may lag behind upstream changes.

Frequently Asked Questions

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