sasso (Ruby)

In-process SCSS / Sass → CSS compilation for Ruby, backed by sasso — a pure-Rust, dependency-free dart-sass alternative that targets byte-for-byte parity with current dart-sass. Shipped as a native extension (Rust via magnus

rb-sys); no Node, no subprocess, no Dart VM.

This gem is the Ruby binding. The compiler core lives in the separate momiji-rs/sasso repo (crate on crates.io); this gem pins it exactly and releases on its own cadence.

Install

# Gemfile
gem "sasso"

$ bundle install

Precompiled native gems ship for common platforms (Linux gnu/musl, macOS, and Windows on x86_64/arm64), so no Rust toolchain is needed. On other platforms the gem compiles from source via cargo (needs a Rust toolchain).

Usage

require "sasso"

Sasso.compile_string("$c: #336699; a { color: $c; &:hover { color: red } }")
# => "a {\n  color: #336699;\n}\na:hover {\n  color: red;\n}\n"

# Minified:
Sasso.compile_string("a { b: 1px }", style: :compressed)   # => "a{b:1px}"

# Indented .sass syntax:
Sasso.compile_string("a\n  b: 1px\n", indented: true)

# A file (syntax inferred from the extension; diagnostics get the file name):
Sasso.compile("app/assets/stylesheets/application.scss",
              style: :compressed, load_paths: ["vendor/stylesheets"])

Options (`compile_string` / `compile`)

Option	Default	Meaning
`style:`	`:expanded`	`:expanded` or `:compressed`
`syntax:`	`:scss`	`:scss`, `:sass`, or `:css`
`indented:`	`false`	shorthand for `syntax: :sass`
`load_paths:`	`[]`	directories searched for `@use`/`@forward`/`@import`
`url:`	`nil`	filename shown in diagnostics (enables the rich dart-style error block)
`alert_ascii:`	`false`	ASCII-only diagnostics

Errors

A compile failure raises Sasso::CompileError (a Sasso::Error < StandardError) whose #message is the compiler's full diagnostic — the same text the sasso CLI prints.

begin
  Sasso.compile_string("a { b: 1px + 1em }")
rescue Sasso::CompileError => e
  warn e.message
end

Conformance & performance

The core passes 100% of the attempted official sass-spec suite byte-for-byte against dart-sass; see the core repo. Compilation is in-process (no IPC), and the engine is heavily perf-tuned (a scoped bump arena, reference-counted values).

License

MIT OR Apache-2.0, matching the core compiler.