Quantum/Stylo

Stylo (a.k.a. Quantum CSS) will integrate Servo's CSS style system into Gecko, such that the style system code can be shared by Gecko and Servo. Stylo V1 will support Firefox on Windows, macOS, and Linux. Android support may ship in a later release.

Stylo is a core part of Project Quantum.

Getting Involved

If you're interested in contributing to Stylo or Servo, drop by the #servo IRC channel on Mozilla's IRC server.

One front where you can help out is adding new properties to Servo's CSS parsing crate. This requires familiarity with Rust, but is otherwise a good way to dip your toes into Servo's style system. To get started, see Servo's CSS property hacking guide for more information.

If you do not know Rust, you can help implement keyword properties. See the Stylo hacking guide for more details. The Stylo hacking guide also has instructions for building Stylo if you wish to play with it yourself. If you know C++, Firefox bug 1277133 has information about easy Gecko bugs that will assist Stylo's integration with Gecko.

Some Stylo bugs that are good for new Servo contributors are tagged on GitHub as “easy” bugs and “less-easy” bugs.

Committing stylo changes

The process for committing a Stylo change that involves both Gecko and Servo changes is as follows:

1. Create a Servo PR with the Servo changes in question.
2. Get that reviewed and checked into Servo's github repository.
3. Wait for servo-vcs-sync to land the Servo changes on Gecko's autoland.
4. Land the Gecko changes on autoland.

Release Criteria

Stylo should not cause us to regress any CSS feature unless we explicitly decide that regressing that specific feature is acceptable. The existing test suite will be the primary benchmark of this, with cross-validation from an automated analysis and manual QA of the Alexa Top 500 sites.

• Stylo should have zero blocking bugs.
• Stylo should pass all (non-disabled) Gecko reftests and mochitests.
• Stylo should have no more unimplemented properties on the Alexa Top 500 sites than Gecko.
• Stylo should pass visual diff testing (bug 1331552) for the Alexa Top 500 (?) sites.
• Stylo's Talos test performance should be faster than or equal to Gecko's.
• Stylo's memory usage (both Talos and beta telemetry) should be less than or equal to Gecko's.
• Stylo's crash rate should be less than or equal to Gecko's.
• Stylo's user engagement ratio (DAU/MAU) should be greater than or equal to Gecko's.

Work Breakdown Structure

• Tests
  • reftests: Shing
  • mochitests: TBD
• Cargo
  • Build Support: Nathan, Ralph
    • Build Stylo: Lars
  • Vendoring Support: Ted, Yehuda
    • Vendor Servo: Lars
• Glue (Gecko/C++/Rust/Servo): Manish, Simon, Xidorn, Michael
• CSS Support
  • CSS Properties: Cameron, Xidorn, Simon, Emilio, Bobby, Brian
  • CSSOM: Xidorn, Simon
• Autoland
  • Servo CI and Autolander: Emily
  • Gecko CI and Autolander: Emily

Milestones

stylo-central

• Run linux64-stylo tests in mozilla-central (bug 1330414) (dependencies)
  • Enable stop-gap vcs sync (bug 1317525)
  • Vendor servo in mozilla-central (bug 1322769)
  • Make all tests green (by skipping or expecting failure)

stylo-nightly

• Enable Stylo in Nightly (bug 1330412) (dependencies)
  • Implement parsing of all CSS properties supported by Firefox
  • Fix and enable all tests (without skipping or expecting failure)
  • Fix all crashes and assertion failures
    • Fuzz Stylo
    • Pass [Auto-tools/Projects/BugHunter Bughunter]
  • Manual QA sign-off
    • Smoke test Alexa Top N sites
    • Exploratory testing of browser UI and features

stylo-release

• Stylo meta bug 1243581 (dependencies)
• Run experiment comparing Stylo vs Gecko on engagement ratio, performance, crash rate, and memory usage.
• Let Stylo ride the trains
  • Enable Stylo on all platforms (bug stylo-nightly)
    • Pass QA on all platforms (tests, fuzzing, BugHunter)
• Ship Stylo to Release

Bugs

Bugzilla Queries

• Unassigned P1-P2 bugs
• P1 stylo: bugs
• P2 stylo: bugs
• P3 stylo: bugs

• Unprioritized "stylo:" bugs to be triaged (Bobby's list)
• Unprioritized "stylo" whiteboard bugs to be triaged (Chris's list)
• All P1-P3 bugs
• All P4 bugs
• All P5 bugs
• All Stylo bugs!
• Bugs by developer

Priority Definitions:

• P1: Stuff we're working on or want to be working on now
• P2: Overflow from P1. Bugs which reduce uncertainty, but which we don't have the resources to staff for now.
• P3: Bugs we need to fix before shipping, but which do not disproportionately reduce uncertainty.
• P4: Want before shipping, but could potentially ship without.
• P5: Not actively prioritized (includes metabugs)

P1 Bugs

Assigned

No results.

0 Total; 0 Open (0%); 0 Resolved (0%); 0 Verified (0%);

Unassigned

No results.

0 Total; 0 Open (0%); 0 Resolved (0%); 0 Verified (0%);

P2 Bugs

Assigned

Full Query

ID	Priority	Summary	Keywords	Assigned to
1406622	P2	stylo: use invalidation framework to handle restyles needed in response to content insertion/removal	perf:responsiveness	Emilio Cobos Álvarez (:emilio)
1420369	P2	stylo: 6.21 - 6.54% remote-tsvg / remote-twitter (android-6-0-armv8-api16, android-7-1-armv8-api16) regression on push db56323cd08f4883e4824199b441a3141be655e5 (Thu Nov 23 2017)	perf, regression	Makoto Kato [:m_kato]

2 Total; 2 Open (100%); 0 Resolved (0%); 0 Verified (0%);

Unassigned

Full Query

ID	Priority	Summary	Keywords	Assigned to
1391341	P2	stylo: Font size inherits differently than in Gecko	dev-doc-complete, regression
1406996	P2	stylo: Investigate crash reports around Rust HashMaps	sec-audit
1413654	P2	stylo: We rely on the initial ResolveStyleFor call when computing the body style for scroll propagation to deal with updating the stylist
1418902	P2	stylo: Stop updating animation data on pseudo elements whose content value is changed to 'none'	reproducible
1422615	P2	stylo: Stop cascading an element for restyling if the element has display:none
1426295	P2	stylo: SVG images use more memory than Gecko
1430706	P2	stylo: geckoservo::glue::Servo_ParseStyleAttribute is slower than Gecko's old CSS parser on ARM

7 Total; 7 Open (100%); 0 Resolved (0%); 0 Verified (0%);

Links

• Stylo build instructions
• Stylo meeting notes