1 stable release

1.5.0 Jun 23, 2022

#133 in Email

22 downloads per month

Unlicense

100KB
2.5K SLoC

Alejandra 💅

The Uncompromising Nix Code Formatter

CI/CD Coverage License: The Unlicense style: Alejandra

Try it on your browser! here

Features

  • ✔️ Fast

    It's written in Rust and formats Nixpkgs in just a few seconds. [^benchmark-specs]

  • ✔️ Powerful

    We define a comprehensive style for all possible combinations of the Nix expression language.

  • ✔️ Reliable

    High coverage, battle tested.

    From Nix's eyes, code is just the same. [^semantic-changes]

  • ✔️ Beautiful

    Beauty is subjective, right?

    We started from the original style of Nixpkgs, and then we applied the feedback of developers who have used Nix at scale for several years, producing a very well-grounded style guide.

  • ✔️ Transparent

    You won't notice the formatter after a while.

    Humans care about the content, machines about the style!

  • ✔️ Native

    We integrate with common code editors and workflows:

Getting started

On the web editor

Please visit: kamadorueda.github.io/alejandra.

Prebuilt binaries

You can download a binary for your platform:

Make it executable ($ chmod +x) and run Alejandra with:

$ ./alejandra --help

or:

$ /path/to/alejandra --help

From Nixpkgs

Please visit: search.nixos.org/packages?query=alejandra.

Nix installation

  • Nix stable:

    $ nix-env -ivf https://github.com/kamadorueda/alejandra/tarball/3.0.0
    
  • Nix with Flakes:

    $ nix profile install github:kamadorueda/alejandra/3.0.0
    

Then run Alejandra with:

$ alejandra --help

NixOS installation

  • Nix stable:

    let
      alejandra =
        (import (builtins.fetchTarball {
          url = "https://github.com/kamadorueda/alejandra/tarball/3.0.0";
          sha256 = "0000000000000000000000000000000000000000000000000000";
        }) {})
        .outPath;
    in {
      environment.systemPackages = [alejandra];
    }
    
  • Nix with Flakes:

    {
      inputs = {
        nixpkgs.url = "github:nixos/nixpkgs/nixpkgs-unstable";
    
        alejandra.url = "github:kamadorueda/alejandra/3.0.0";
        alejandra.inputs.nixpkgs.follows = "nixpkgs";
      };
    
      outputs = {alejandra, nixpkgs, ...}: {
        nixosConfigurations = {
          example = nixpkgs.lib.nixosSystem rec {
            # We support: aarch64-darwin, aarch64-linux, i686-linux, x86_64-darwin, x86_64-linux
            system = "x86_64-linux";
    
            modules = [
              {
                environment.systemPackages = [alejandra.defaultPackage.${system}];
              }
              # Import your other modules here
              # ./path/to/my/module.nix
              # ...
            ];
          };
        };
      };
    }
    

Do I need to configure anything?

  • No.

Discussion

Cool libraries

Alternatives

See why Alejandra was created and a comparison between alternatives here.

Alternatively, checkout the code examples of the different formatters here.

Versioning

We use semver to version Alejandra.

Our public API consists of:

  • The formatting rules (a.k.a. the style).
  • The CLI tool ($ alejandra), command line flags, positional arguments, exit codes, and stdout.

Changelog

Please read: CHANGELOG.

Contributors

The following people have helped improving Alejandra.

Thank you ❤️

Footnotes

[^benchmark-specs]: Running on a machine with:

- CPU: 4 physical, 4 logical, 11th Gen Intel(R) Core(TM) i7-1165G7 @ 2.80GHz
- MHz: from 400 to 4700 MHz
- BogoMips: 5606.40
- Cache L3: 12 MiB

Using:

```bash
# x86_64-unknown-linux-gnu
$ time alejandra --threads $threads /path/to/nixpkgs
```

Results:

| $threads | Seconds |
| :------: | :-----: |
|    1     |   45    |
|    2     |   25    |
|    4     |   14    |

[^semantic-changes]: The methodology to claim this is:

1.  Checkout [Nixpkgs](https://github.com/nixos/nixpkgs) and run:

    ```bash
    $ nix-env -qaf . --drv-path --xml > before
    ```

1.  Now format with Alejandra and run:

    ```bash
    $ nix-env -qaf . --drv-path --xml > after
    ```

As of 2022-06-22,
there are 41 differences in a set of 38109 derivations
because of things like this:

```
goDeps = ./deps.nix;
```

Since `./deps.nix` was also formatted
you get a semantical difference.

This is something that should be solved on Nixpkgs
and not a bug in Alejandra.
For example:

- https://github.com/NixOS/nixpkgs/pull/178378
- https://github.com/NixOS/nixpkgs/pull/157760

Dependencies

~1MB
~17K SLoC