Stylo

High-Performance CSS Style Engine

Stylo is a high-performance, browser-grade CSS style engine written in Rust that powers Servo and Firefox. This repo contains Servo’s downstream version of Stylo. The upstream version lives in mozilla-central with the rest of the Gecko/Firefox codebase.

Coordination of Stylo development happens:

• Here in Github Issues
• In the #stylo channel of the Servo Zulip
• In the #layout room of the Mozilla Matrix instance (matrix.mozilla.org)

High-Level Documentation

• This Mozilla Hacks article contains a high-level overview of the Stylo architecture.
• There is a chapter in the Servo Book (although it is a little out of date).

Branches

The branches are as follows:

• upstream has upstream mozilla-central filtered to the paths we care about (style.paths), but is otherwise unmodified.
• main adds our downstream patches, plus the scripts and workflows for syncing with mozilla-central on top of upstream.

[!WARNING] This repo syncs from upstream by creating a new branch and then rebasing our changes on top of it. This means that git pull will not work across syncs (you will need to use git fetch, git reset and git rebase).

More information on the syncing process is available in SYNCING.md

Crates

A guide to the crates contained within this repo

Stylo Crates

These crates are largely implementation details of Stylo, although you may need to use some of them directly if you use Stylo.

Directory	Crate	Notes
style		The main Stylo crate containing the entire CSS engine
style_traits		Types and traits which allow other code to interoperate with Stylo without depending on the main crate directly.
stylo_dom		Similar to stylo_traits (but much smaller)
stylo_atoms		Atoms for CSS and HTML event related strings
stylo_config		Configuration for Stylo. Can be used to set runtime preferences (enabling/disabling properties, etc)
stylo_static_prefs		Static configuration for Stylo. Config be overridden by patching in a replacement crate.
style_derive		Internal derive macro for stylo crate

Standalone Crates

These crates form part of Stylo but are also be useful standalone.

Directory	Crate	Notes
selectors		CSS Selector matching
servo_arc		A variant on std::Arc

You may also be interested in the cssparser crate which lives in the servo/rust-cssparser repo.

Support Crates

Low-level crates which could technically be used standalone but are unlikely to be generally useful in practice.

Directory	Crate	Notes
malloc_size_of		Heap size measurement for Stylo values
to_shmem		Internal utility crate for sharing memory across processes.
to_shmem_derive		Internal derive macro for to_shmem crate

Building Servo Against a Local Copy of Stylo

Assuming your local servo and stylo directories are siblings, you can build servo against stylo by adding the following to servo/Cargo.toml:

[patch."https://github.com/servo/stylo"]
selectors = { path = "../stylo/selectors" }
servo_arc = { path = "../stylo/servo_arc" }
stylo_atoms = { path = "../stylo/stylo_atoms" }
stylo = { path = "../stylo/style" }
stylo_config = { path = "../stylo/stylo_config" }
stylo_dom = { path = "../stylo/stylo_dom" }
stylo_malloc_size_of = { path = "../stylo/malloc_size_of" }
stylo_traits = { path = "../stylo/style_traits" }

Releases

Releases are made every time this repository rebases its changes on top of the latest version of upstream Stylo. There are a lot of crates here. In order to publish them, they must be done in order. One order that works is:

• selectors
• stylo_static_prefs
• stylo_config
• stylo_atoms
• stylo_malloc_size_of
• stylo_dom
• stylo_derive
• stylo_traits
• stylo

License

Stylo is licensed under MPL 2.0