This month in Servo: dark mode, keyword sizes, XPath, and more!

CSS transitions can now be triggered properly by script (@mrobinson, #34486), and we now support ‘min-height’ and ‘max-height’ on column flex containers (@Loirooriol, @mrobinson, #34450), ‘min-content’, ‘max-content’, ‘fit-content’, and ‘stretch’ in block layout (@Loirooriol, #34641, #34568, #34695), ‘stretch’ on replaced positioned elements (@Loirooriol, #34430), as well as ‘align-self: self-start’, ‘self-end’, ‘left’, and ‘right’ on positioned elements (@taniishkaaa, @Loirooriol, #34365).

We now support console.trace() (@simonwuelker, #34629), PointerEvent (@wusyong, #34437), and the clonable property on ShadowRoot (@simonwuelker, #34514). Shadow DOM support continues to improve (@jdm, #34503), including very basic Shadow DOM layout (@mrobinson, #34701) when enabled via --pref dom.shadowdom.enabled.

script underwent (and continues to undergo) major rework towards being more reliable and faster to build. We’ve landed better synchronisation for DOM tree mutations (@jdm, #34505) and continued work on splitting up the script crate (@jdm, #34366). We’ve moved our ReadableStream support into Servo, eliminating the maintenance burden of a downstream SpiderMonkey patch (@gterzian, @wusyong, @Taym95, #34064, #34675).

The web platform guarantees that same-origin frames and their parents can synchronously observe resizes and their effects. Many tests rely on this, and not doing this correctly made Servo’s test results much flakier than they could otherwise be. We’ve made very good progress towards fixing this (@mrobinson, #34643, #34656, #34702, #34609), with correct resizing in all cases except when a same-origin frame is in another script thread, which is rare.

Servo’s performance continues to improve, with layout caching for flex columns delivering up to 12x speedup (@Loirooriol, @mrobinson, #34461), many unnecessary reflows now eliminated (@mrobinson, #34558, #34599, #34576, #34645), reduced memory usage (@mrobinson, @Loirooriol, #34563, #34666), faster rendering for pages with animations (@mrobinson, #34489), and timers now operating without IPC (@mrobinson, #34581).

servoshell nightlies are up to 20% smaller (@atbrakhi, #34340), WebGPU is now optional at build time (@atbrakhi, #34444), and --features tracing no longer enables --features layout-2013 (@jschwe, #34515) for further binary size savings. You can also limit the size of several of Servo’s thread pools with --pref threadpools.fallback_worker_num and others (@jschwe, #34478), which is especially useful on machines with many CPU cores.

We’ve started laying the groundwork for full incremental layout in our new layout engine, starting with a general layout caching mechanism (@mrobinson, @Loirooriol, #34507, #34513, #34530, #34586). This was lost in the switch to our new layout engine, and without it, every time a page changes, we have to rerun layout from scratch. As you can imagine, this is very, very expensive, and incremental layout is critical for performance on today’s highly dynamic web.