Opinionated sorting for TailwindCSS classes used in HEEx templates and ~H sigils.

TailwindFormatter is a mix format plugin that sorts TailwindCSS classes found in your templates. It takes inspiration from Tailwind's official Prettier plugin.

Note: This formatter requires Elixir v1.15 or later.

Installation

Add tailwind_formatter to your list of dependencies in mix.exs:

def deps do
  [
    {:tailwind_formatter, "~> 0.4.0", only: [:dev, :test], runtime: false}
  ]
end

Setup

TailwindFormatter is most likely to be used alongside Phoenix.LiveView.HTMLFormatter, so it should be installed in a way that allows the HTML formatter to run after the Tailwind formatter.

Update your .formatter.exs to include TailwindFormatter.

  [
    plugins: [TailwindFormatter, Phoenix.LiveView.HTMLFormatter],
    inputs: [
      "*.{heex,ex,exs}",
      "priv/*/seeds.exs",
      "{config,lib,test}/**/*.{heex,ex,exs}"
    ],
    # ...
  ]

Using Custom TailwindCSS configuration

If you are using the standalone tailwind module, you can append these lines to the end of your tailwind.config.js file:

let { extract } = require("../deps/tailwind_formatter/assets/js")
extract(module.exports, "../_build")

This will write a classes.txt and variants.txt to your _build/ directory. The second argument within extract may vary depending on the value of cd: in your :tailwind config.

The above will work with this configuration, for example:

  config :tailwind,
    version: "3.3.3",
    default: [
      args: ~w(
      --config=tailwind.config.js
      --input=css/app.css
      --output=../_build/assets/out.css
    ),
      cd: Path.expand("../assets", __DIR__)
    ]

Run mix tailwind default to force it to extract the configuration.

Afterward, when you run mix compile you should see TailwindFormatter loading in your custom classes. If you don't, you can run mix deps.compile tailwind_formatter --force.

❯ mix deps.compile tailwind_formatter --force
==> tailwind_formatter
Compiling 5 files (.ex)
Loading in /path/to/repo/_build/classes.txt.
Loading in /path/to/repo/_build/variants.txt.
Generated tailwind_formatter app

Usage

After installation and setup, run mix format. If you already had automatic formatting set up (for instance, if your editor is configured to format your code on save), no changes should be required! Your Tailwind classes should be happily organized going forward!

If some files are not being formatted as expected, double-check the :inputs option in your .formatter.exs to ensure they are being matched.

Formatting

The formatter aims to follow a bundle of rules outlined in the blog post that introduced the official Tailwind Prettier plugin.

• Order classes the same way they are imported in the CSS file: Base, Components, Utilities
• Classes that override other classes appear later in the list
• Classes that impact layout take precedence over classes that decorate
• Plain classes come first before variants (i.e. focus:)
• Unknown classes are sorted to the front

How it diverges from the original formatter

There are some differences in order to simplify the algorithm and to support Elixir use cases.

Inline elixir functions are sorted toward the front

With elixir templating one may add an #{inline_elixir_function} to the class list. The formatter supports this and sorts these toward the front.

Variants are always grouped, even if the class is unknown

i.e. sm:unknown-class will still be grouped with the other sm: variants, even if Tailwind doesn't recognize the class.

Variant order is enforced

In the original spec, 'variants' i.e. sm:hover: are sorted as though it is one block. Thus, the order in which they're specified does not matter. So, for example, a chain of dark:sm:hover:text-gray-600 would be placed toward the end.

In this algorithm, classes are sorted by "layers". All sm: variants are grouped together, even if it's a chain of 4 variants. So for example, dark:sm:hover:text-gray-600 will be placed before any sm: and hover: variants, because dark: has precedence over sm: and hover:.

Thus in order to achieve more consistency, the variant chain is ordered. So, dark:sm:hover:text-gray-600 transforms to sm:dark:hover:text-gray-600.

Dynamically rendered classes

Sometimes you may want to dynamically render a class depending on a variable, i.e. lg:grid-cols-#{@cols} or alert alert-#{@type}. The formatter supports this, and also sorts these toward the front of the variant group it is within.

Note: you will need to define the full class either within the Tailwind safelist or have it fully written out somewhere else in the source file.

So, for example, if @cols = 5 within grid-cols-#{@cols}, then you will need grid-cols-5 written in full somewhere in the source so Tailwind won't purge it in production.

Credits

This project builds heavily off of rustywind and HTMLFormatter.