Servo 2023

Quick recap

• Started in 2012 by Mozilla as a research project
• Since then, Servo has been a vehicle for
  • developing the Rust language
  • experimenting with parallelism
  • taking those lessons back to Firefox
• …and then the layoffs happened

Servo and Firefox

What now?

• Servo is…
  • an independent web engine
  • written (almost) entirely in Rust
  • with parallelism in style and layout
  • designed for modularity from the start
  • designed to allow embedding in the future
• What can we do with that? [What new purposes can Servo bring to the table?]

Servo <3 embedded

• We need more web engine diversity
• But general-purpose engine diversity means taking on
  Apple, Google, and Mozilla
• On the other hand, the embedded web engine space…
  • is even less diverse — WPE (WebKit) and CEF (Chromium) are the only major players
  • allows for use cases with restricted content

Since the start of 2023

• Restarted the Technical Steering Committee
• Started reconciling the two layout engines
• 328 patches landed in servo/servo alone (vs 223 in 2022)
  • Many improvements to builds and releases
  • Several big dependency updates
  • WPT failures and flaky tests
  • New impl work on Layout 2020
  • Non-Igalia contributors in bold :)

Technical Steering Committee

• Oversees Servo’s
  • Committers and other roles
  • Design and architecture
  • Infrastructure, outreach, …
• Now meets monthly (dates and times announced on Zulip)
• Anyone can raise points to discuss on GitHub
• Minutes published live on Zulip and on GitHub

Reconciling layout engines

• Layout 2013 still the default, Layout 2020 was left unfinished
• everything between DOM+style and WebRender
• 2020 does not yet support floats or incremental layout
• 2020 uses opportunistic parallelism, not eager parallelism
• 2020 splits flow tree into separate box and fragment trees
• 2020 generates a WebRender display list directly
• 2020 better aligns its naming and architecture with specs

Reconciling layout engines

• We propose a gradual transition to Layout 2020
  1. Improve support for Layout 2020 in CI and releases
  2. Implement some smaller features in Layout 2020
  3. Decision time: should we remove Layout 2013?
  4. Implement floats and other complex features
• More details in our report

WPT failures and flaky tests

• Retry unexpected results to find random flakes (mrobinson)
• Support for giving tests multiple expectations (mrobinson)
• Fixed flakiness in scrolling (mrobinson)
• Fixed flakiness in hit testing (mrobinson)
• Fixed flakiness in animations (mrobinson)
• Named access on the window object (pylbrecht, yvt, delan)
• (wip) CSS Font Loading API (mukilan)

Builds and releases

• New test result comments on pull requests (mrobinson)
• New intermittents dashboard for flaky tests (delan)
• Several improvements to builds in forks (sagudev)
• Several improvements to WPT upstreaming (mrobinson)
• mach try (sagudev)
• sccache on Linux and macOS (sagudev)

Dependency updates

• truetype crate (IvanUkhov)
• Python 3.11 (andreubotella)
• Rust toolchain (mukilan)
• euclid crate (mrobinson)

• winit crate (atomgardner)
• WebIDL.py (sagudev)
• many crate dedupes (atouchet)
• (wip) WebRender (mrobinson)

New progress on Layout 2020

• mach support (mrobinson)
• partial CI support (mrobinson)
• iframes (mrobinson)
• ‘{min,max}-width’ + ‘{min,max}-height’ (delan)
• ‘text-indent’ (Loirooriol)
• ‘outline’ + ‘outline-offset’ (Loirooriol)
• ‘text-decoration’ improvements (Loirooriol)

Next up for Layout 2020

• position: sticky
• ‘vertical-align’
• ‘white-space’
• counters
• floats (eventually) [floats are the “boss fight”]

Servo on wpt.fyi

• wpt.fyi → EDIT → ADD PRODUCT → Servo → SUBMIT
• Great for drilling down specs → tests → subtests
• Not so great for tracking progress over time
  (but it’s possible)
• Layout 2013 only for now, Layout 2020 coming soon

Servo WPT dashboard

• Tracks progress over time
• Supports both Layout 2013 and 2020
• Has filters for our focus areas:
  • CSS2: abspos, box-display, floats, linebox, margin-padding-clear, normal-flow, positioning
  • CSSOM
  • CSS Position

Demos in Layout 2020

• Comparisons with Layout 2013
  • Acid1 [essentially correct minus floats]
  • Acid2 [gnarly, but makes sense if you adjust for features not yet supported in layout 2020]

Demos in Layout 2020

• Servo Experiments — demo.servo.org
  • Mosaic Gallery — parallel style
  • TWGL Tunnel — WebGL

Demos in Layout 2020

Contributing

• HACKING_QUICKSTART.md + Zulip
• Hack on layout (maybe after we switch to Layout 2020)
• Hack on other parts of Servo too :)
  • especially DOM, CSSOM, navigation, iframes, devtools
  • #29831 — Devtools support is broken
• Make cool demos for Servo Experiments
• Report any bugs you find on GitHub