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https://github.com/numtide/treefmt-nix

treefmt nix configuration
https://github.com/numtide/treefmt-nix

buildbot-numtide flake-parts nix treefmt

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treefmt nix configuration

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README 

        



# treefmt-nix






**Fast and convenient multi-file formatting with Nix**



_A numtide project._





Static Badge









[treefmt](https://numtide.github.io/treefmt) combines file formatters for

multiple programming languages so that you can format all your project files

with a single command. With `treefmt-nix` you can specify `treefmt` build

options, dependencies and config in one place, conveniently managed by

[Nix](https://nixos.org/).



`treefmt-nix` automatically installs and configures the desired formatters as

well as `treefmt` for you and integrates nicely into your Nix development

environments. It comes with sane, pre-crafted

[formatter-configs](https://github.com/numtide/treefmt-nix/tree/main/programs)

maintained by the community; each config corresponds to a section that you would

normally add to the `treefmt` config file `treefmt.toml`.



Take a look at the already [supported formatters](#supported-programs) for

Python, Rust, Go, Haskell and more.



## Integration into Nix



### Nix classic without flakes



To run `treefmt-nix` with nix-classic, import the repo using

[`niv`](https://github.com/nmattia/niv):



```

$ niv add numtide/treefmt-nix

```



Alternatively, you can download the source and run `nix-build` in the project

root directory:



```

$ nix-build

```



The command will return the helper functions which will be later used to produce

a derivation from the specified `treefmt-nix` configuration.



After you installed treefmt-nix, specify the formatter configuration. For

instance, this one is for formatting terraform files:



```nix

# myfile.nix

{ system ? builtins.currentSystem }:

let

  nixpkgsSrc = builtins.fetchTarball "https://github.com/NixOS/nixpkgs/archive/refs/heads/nixos-unstable.tar.gz";

  treefmt-nixSrc = builtins.fetchTarball "https://github.com/numtide/treefmt-nix/archive/refs/heads/master.tar.gz";

  nixpkgs = import nixpkgsSrc { inherit system; };

  treefmt-nix = import treefmt-nixSrc;

in

treefmt-nix.mkWrapper nixpkgs {

  # Used to find the project root

  projectRootFile = ".git/config";

  # Enable the terraform formatter

  programs.terraform.enable = true;

  # Override the default package

  programs.terraform.package = nixpkgs.terraform_1;

  # Override the default settings generated by the above option

  settings.formatter.terraform.excludes = [ "hello.tf" ];

}

```



It's a good practice to place the configuration file in the project root

directory.



Next, execute this command:



```

$ nix-build myfile.nix

```



This command returns a derivation that contains a `treefmt` binary at

`./result/bin/treefmt` in your current directory. The file is actually a symlink

to the artifact in `/nix/store`.



`treefmt.toml` in this case isn't generated: the binary is wrapped with the

config.



### Flakes



Running treefmt-nix with flakes isn't hard. The library is exposed as the `lib`

attribute:



```nix

# flake.nix

{

  inputs.treefmt-nix.url = "github:numtide/treefmt-nix";



  outputs = { self, nixpkgs, systems, treefmt-nix }:

    let

      # Small tool to iterate over each systems

      eachSystem = f: nixpkgs.lib.genAttrs (import systems) (system: f nixpkgs.legacyPackages.${system});



      # Eval the treefmt modules from ./treefmt.nix

      treefmtEval = eachSystem (pkgs: treefmt-nix.lib.evalModule pkgs ./treefmt.nix);

    in

    {

      # for `nix fmt`

      formatter = eachSystem (pkgs: treefmtEval.${pkgs.system}.config.build.wrapper);

      # for `nix flake check`

      checks = eachSystem (pkgs: {

        formatting = treefmtEval.${pkgs.system}.config.build.check self;

      });

    };

}

```



And also add the `treefmt.nix` file (or put the content inline if you prefer):



```nix

# treefmt.nix

{ pkgs, ... }:

{

  # Used to find the project root

  projectRootFile = "flake.nix";

  # Enable the terraform formatter

  programs.terraform.enable = true;

  # Override the default package

  programs.terraform.package = pkgs.terraform_1;

  # Override the default settings generated by the above option

  settings.formatter.terraform.excludes = [ "hello.tf" ];

}

```



This file is also the place to define all the treefmt parameters like includes,

excludes and formatter options.



After specifying the flake, run

[`nix fmt`](https://nixos.org/manual/nix/stable/command-ref/new-cli/nix3-fmt.html):



```

$ nix fmt

```



Nix-fmt is a tool to format all nix files in the project, but with the specified

flake, it starts treefmt-nix and formats your project.



You can also run `nix flake check` (eg: in CI) to validate that the project's

code is properly formatted.



### Flake-parts



This flake exposes a [flake-parts](https://flake.parts/) module as well. To use

it:



1. Add `inputs.treefmt-nix.flakeModule` to the `imports` list of your

   `flake-parts` call.



2. Add `treefmt = { .. }` (containing the configuration above) to your

   `perSystem`.



As an example, see



## Configuration



While dealing with `treefmt` outside of `nix`, the formatter configuration is

specified in a `toml` format. On the contrary, with `nix`, you write in with a

nix syntax like this:



```nix

# Used to find the project root

projectRootFile = ".git/config";

# Enable the terraform formatter

programs.terraform.enable = true;

# Override the default package

programs.terraform.package = nixpkgs.terraform_1;

# Override the default settings generated by the above option

settings.formatter.terraform.excludes = [ "hello.tf" ];

```



**Options:**



- `Project root file` is the git file of the project which you plan to format.

- The option `programs.terraform.enable` enables the needed formatter. You can

  specify as many formatter as you want. For instance:



```

programs.terraform.enable = true;

programs.gofmt.enable = true;

```



- The option `programs.terraform.package` allows you to use a particular

  build/version of the specified formatter.

- By setting`settings.formatter.terraform.excludes` you can mark the files which

  should be excluded from formatting. You can also specify other formatter

  options or includes this way.



For detailed description of the options, refer to the `treefmt`

[documentation](https://treefmt.com/latest/getting-started/configure/).



## Project structure



This repo contains a top-level `default.nix` that returns the library helper

functions.



- `mkWrapper` is the main function which wraps treefmt with the needed

  configuration.

- `mkConfigFile`

- `evalModule`

- `all-modules`



## Supported programs



`treefmt-nix` currently supports 97 formatters:



* [actionlint](programs/actionlint.nix)

* [alejandra](programs/alejandra.nix)

* [asmfmt](programs/asmfmt.nix)

* [beautysh](programs/beautysh.nix)

* [biome](programs/biome.nix)

* [black](programs/black.nix)

* [buildifier](programs/buildifier.nix)

* [cabal-fmt](programs/cabal-fmt.nix)

* [clang-format](programs/clang-format.nix)

* [cljfmt](programs/cljfmt.nix)

* [cmake-format](programs/cmake-format.nix)

* [csharpier](programs/csharpier.nix)

* [cue](programs/cue.nix)

* [d2](programs/d2.nix)

* [dart-format](programs/dart-format.nix)

* [deadnix](programs/deadnix.nix)

* [deno](programs/deno.nix)

* [dhall](programs/dhall.nix)

* [dnscontrol](programs/dnscontrol.nix)

* [dos2unix](programs/dos2unix.nix)

* [dprint](programs/dprint.nix)

* [elm-format](programs/elm-format.nix)

* [erlfmt](programs/erlfmt.nix)

* [fantomas](programs/fantomas.nix)

* [fish_indent](programs/fish_indent.nix)

* [fnlfmt](programs/fnlfmt.nix)

* [formatjson5](programs/formatjson5.nix)

* [fourmolu](programs/fourmolu.nix)

* [fprettify](programs/fprettify.nix)

* [gdformat](programs/gdformat.nix)

* [genemichaels](programs/genemichaels.nix)

* [gleam](programs/gleam.nix)

* [gofmt](programs/gofmt.nix)

* [gofumpt](programs/gofumpt.nix)

* [goimports](programs/goimports.nix)

* [google-java-format](programs/google-java-format.nix)

* [hclfmt](programs/hclfmt.nix)

* [hlint](programs/hlint.nix)

* [isort](programs/isort.nix)

* [jsonfmt](programs/jsonfmt.nix)

* [jsonnet-lint](programs/jsonnet-lint.nix)

* [jsonnetfmt](programs/jsonnetfmt.nix)

* [just](programs/just.nix)

* [keep-sorted](programs/keep-sorted.nix)

* [ktfmt](programs/ktfmt.nix)

* [ktlint](programs/ktlint.nix)

* [latexindent](programs/latexindent.nix)

* [leptosfmt](programs/leptosfmt.nix)

* [mdformat](programs/mdformat.nix)

* [mdsh](programs/mdsh.nix)

* [meson](programs/meson.nix)

* [mix-format](programs/mix-format.nix)

* [muon](programs/muon.nix)

* [mypy](programs/mypy.nix)

* [nickel](programs/nickel.nix)

* [nimpretty](programs/nimpretty.nix)

* [nixfmt-classic](programs/nixfmt-classic.nix)

* [nixfmt-rfc-style](programs/nixfmt-rfc-style.nix)

* [nixfmt](programs/nixfmt.nix)

* [nixpkgs-fmt](programs/nixpkgs-fmt.nix)

* [nufmt](programs/nufmt.nix)

* [ocamlformat](programs/ocamlformat.nix)

* [odinfmt](programs/odinfmt.nix)

* [opa](programs/opa.nix)

* [ormolu](programs/ormolu.nix)

* [packer](programs/packer.nix)

* [perltidy](programs/perltidy.nix)

* [php-cs-fixer](programs/php-cs-fixer.nix)

* [pinact](programs/pinact.nix)

* [prettier](programs/prettier.nix)

* [protolint](programs/protolint.nix)

* [purs-tidy](programs/purs-tidy.nix)

* [rubocop](programs/rubocop.nix)

* [ruff-check](programs/ruff-check.nix)

* [ruff-format](programs/ruff-format.nix)

* [rufo](programs/rufo.nix)

* [rustfmt](programs/rustfmt.nix)

* [scalafmt](programs/scalafmt.nix)

* [shellcheck](programs/shellcheck.nix)

* [shfmt](programs/shfmt.nix)

* [sqlfluff](programs/sqlfluff.nix)

* [sqruff](programs/sqruff.nix)

* [statix](programs/statix.nix)

* [stylish-haskell](programs/stylish-haskell.nix)

* [stylua](programs/stylua.nix)

* [swift-format](programs/swift-format.nix)

* [taplo](programs/taplo.nix)

* [templ](programs/templ.nix)

* [terraform](programs/terraform.nix)

* [texfmt](programs/texfmt.nix)

* [toml-sort](programs/toml-sort.nix)

* [typos](programs/typos.nix)

* [typstfmt](programs/typstfmt.nix)

* [typstyle](programs/typstyle.nix)

* [yamlfmt](programs/yamlfmt.nix)

* [zig](programs/zig.nix)

* [zprint](programs/zprint.nix)



For non-Nix users, you can also find the generated examples in the

[./examples](./examples) folder.



### Using a custom formatter



It is also possible to use custom formatters with `treefmt-nix`. For example,

the following custom formatter formats JSON files using `yq-go`:



```nix

settings.formatter = {

  "yq-json" = {

    command = "${pkgs.bash}/bin/bash";

    options = [

      "-euc"

      ''

        for file in "$@"; do

          ${lib.getExe yq-go} -i --output-format=json $file

        done

      ''

      "--" # bash swallows the second argument when using -c

    ];

    includes = [ "*.json" ];

  };

};

```



### Adding new formatters



PRs to add new formatters are welcome!



- The formatter should conform to the

  [formatter specifications](https://numtide.github.io/treefmt/formatter-spec).

- This is not the place to debate formatting preferences. Please pick defaults

  that are standard in your community -- for instance, python is usually

  indented with 4 spaces, so don't add a python formatter with 2 spaces as the

  default.



In order to add a new formatter do the following things:



1. Create a new entry in the `./programs/` folder.

2. Consider adding yourself as the `meta.maintainer` (see below).

3. Run `./examples.sh` to update the `./examples` folder.

4. To test the program:

   1. Extend the project's `./treefmt.nix` file (temporarily) to enable the new

      formatter and configure it in whatever manner is appropriate.

   2. Add a bunch of pertinent sources in this repo -- for instance, if the new

      formatter is meant to format `*.foo` files, add a number of `*.foo` files,

      some well-formatted (and therefore expected to be exempt from modification

      by `treefmt`) and some badly-formatted.

   3. Run `nix fmt`. Confirm that well-formatted files are unchanged and that

      badly-formatted files are flagged as such. Re-run `nix fmt` and confirm

      that no additional changes were made.

   4. Once this is good, revert those changes.

5. Submit the PR!



### Definition of a `meta.maintainer`



You can register your desire to help with a specific formatter by adding your

GitHub handle to the module's `meta.maintainers` list.



That mostly means, for the given formatter:



- You get precedence if any decisions need to be made.

- Getting pinged if any issue is being found.



## Commercial support



Looking for help or customization?



Get in touch with Numtide to get a quote. We make it easy for companies to work

with Open Source projects: 



## License



All the code and documentation is licensed with the MIT license.