fugo-sass

A Sass compiler written purely in Rust: a library with a very small API (two functions) and a binary intended as a replacement for the Sass command-line executable.

fugo-sass is a fork of grass by Connor Skees, maintained by the fugo project, which compiles its sites' Sass with it. grass has had no release since 0.13.4 (August 2024). fugo-sass carries on from there: 0.14.0 is grass 0.13.4 with the fixes listed in the CHANGELOG, and later releases follow newer versions of dart-sass.

The goal is complete feature parity with the dart-sass reference implementation. A deviation from dart-sass is a bug, except in the case of error messages and error spans.

Documentation
crates.io

Usage

fn main() -> Result<(), Box<fugo_sass::Error>> {
    let css = fugo_sass::from_string(
        "a { b { color: &; } }".to_owned(),
        &fugo_sass::Options::default(),
    )?;
    assert_eq!(css, "a b {\n  color: a b;\n}\n");
    Ok(())
}

cargo install fugo-sass
fugo-sass input.scss

Migrating from grass

The API is grass's. Renaming the dependency keeps every grass:: path working:

[dependencies]
grass = { package = "fugo-sass", version = "0.15" }

The crates were renamed: grass is fugo-sass (binary fugo-sass), grass_compiler is fugo-sass-compiler, and include_sass is fugo-sass-macro.

Status

One can be quite confident in fugo-sass's output. For the average user there should not be perceptible differences from dart-sass. Every commit compiles Bootstrap 5.0.2 and 5.3.3, and CI checks the differences from dart-sass 1.105.1's CSS against a list that may only shrink (crates/spec).

fugo-sass is moving from dart-sass 1.54.3, which grass 0.13.4 targeted, to 1.105.1: the CHANGELOG says what already follows 1.105.1, and the failing specs (crates/spec/failures.txt) what does not yet.

There are a number of known missing features and bugs. The rough edges largely include @forward and more complex uses of @use. Basic usage of these rules is supported, but more advanced features such as @importing modules containing @forward with prefixes may not behave as expected. grass tracked its known gaps in connorskees/grass#19.

fugo-sass is not a drop-in replacement for libsass and does not intend to be. If you are upgrading from libsass, you may have to modify your stylesheets, though these changes should not differ from those you would have to make if upgrading to dart-sass.

Performance

grass was benchmarked against dart-sass and sassc (libsass) here, where it appeared to be ~2x faster than dart-sass and ~1.7x faster than sassc.

Cargo Features

commandline

(enabled by default): build a binary using clap

random

(enabled by default): enable the builtin functions random([$limit]) and unique-id()

macro

(disabled by default): enable the macro fugo_sass::include! for compiling Sass to CSS at compile time

nightly

(disabled by default): currently only used by fugo_sass::include! to enable proc_macro::tracked_path

Testing

As much as possible this library attempts to follow the same philosophy for testing as rust-analyzer. Namely, all one should have to do is run cargo test to run all its tests. This library maintains a test suite distinct from the sass-spec, though it does include some spec tests verbatim. This has the benefit of allowing tests to be run without ruby as well as allowing the tests more granular than they are in the official spec.

Having said that, the official test suite runs with cargo spec, which needs only Rust (crates/spec):

git clone https://github.com/getfugo/fugo-sass --recursive
cd fugo-sass && cargo spec

The sass-spec submodule is pinned to the specs of dart-sass 1.105.1, the release fugo-sass works towards. There fugo-sass passes 8,612 of the 14,347 specs that apply to dart-sass (60%): most of the 5,735 failures are the color functions, mostly for the CSS Color 4 color spaces (5,194). CI checks that the failing specs are exactly those of crates/spec/failures.txt.

Versioning

The crates use the 2024 edition. The minimum supported Rust version (MSRV) is 1.99.0, the latest stable Rust, which CI tests and lints with. An increase to the MSRV will correspond with a minor version bump.

An increase to the targeted dart-sass version will correspond to either a minor or bugfix version bump, depending on the changes.

fugo-sass 0.15.1