WEFT_OS/crates/weft-servo-shell/SERVO_PIN.md

Servo Pin

Current pin

Field	Value
Source	https://github.com/marcoallegretti/servo (fork of servo/servo)
Branch	servo-weft
Rev	04ca254f843ed650d3e5b14e5693ad51a60cc84b (servo-weft tip, 2026-03-11)
Crate	servo (package name as of 2026-03-11; previously libservo)
Feature	servo-embed (optional; off by default)

Adding the Cargo dependencies

The Servo deps are not in Cargo.toml by default to avoid pulling the Servo monorepo (~1 GB) into every cargo check cycle. To activate, add the following to crates/weft-servo-shell/Cargo.toml and change the servo-embed feature line to declare dep:servo, dep:winit, and dep:softbuffer:

[features]
servo-embed = ["dep:servo", "dep:winit", "dep:softbuffer"]

[dependencies.servo]
git = "https://github.com/marcoallegretti/servo"
branch = "servo-weft"
optional = true
default-features = false

[dependencies.winit]
version = "0.30"
optional = true
features = ["wayland"]

[dependencies.softbuffer]
version = "0.4"
optional = true

Then build:

cargo build -p weft-servo-shell --features servo-embed

The first build downloads and compiles Servo and its dependencies, which takes 30–60 minutes cold. Subsequent incremental builds are faster.

System dependencies

The following system packages are required when servo-embed is enabled:

• libgles2-mesa-dev or equivalent OpenGL ES headers
• libssl-dev
• libdbus-1-dev
• libudev-dev
• libxkbcommon-dev
• libwayland-dev

On Fedora/RHEL: mesa-libGL-devel openssl-devel dbus-devel systemd-devel libxkbcommon-devel wayland-devel

Rendering approach

Default: SoftwareRenderingContext (CPU rasterisation) blitted to a softbuffer-backed winit window.

EGL path (scaffolded): set WEFT_EGL_RENDERING=1 at runtime. The embedder attempts WindowRenderingContext::new using the winit display and window handles. If construction fails it falls back to software automatically. When the EGL path is active Servo presents directly to the EGL surface; the softbuffer blit is skipped. Full DMA-BUF export to the Wayland compositor is not yet wired (RenderingCtx::Egl blit body is a no-op).

Known gaps at this pin

• GAP-1: Wayland input events not forwarded to Servo Resolved — keyboard and mouse events forwarded via webview.notify_input_event; key mapping in keyutils.rs.
• GAP-2: EGL WindowRenderingContext path scaffolded (WEFT_EGL_RENDERING=1); DMA-BUF export to the Wayland compositor (linux-dmabuf-unstable-v1) not yet wired.
• GAP-3: WebGPU adapter on Mesa may fail CTS — validation task, requires Mesa GPU hardware.
• GAP-4: CSS Grid Grid resolved (Taffy-backed, fully wired). CSS backdrop-filter unimplemented backdrop-filter resolved (servo/servo issue #41567). Implemented across two commits:
  • marcoallegretti/stylo servo-weft f1ba496: removed servo_pref = "layout.unimplemented" from backdrop-filter in style/properties/longhands.toml (enables parsing).
  • marcoallegretti/servo servo-weft 8e7dc40: Cargo.toml patched to use the stylo fork; style_ext.rs adds backdrop-filter to establishes_stacking_context and establishes_containing_block_for_all_descendants; stacking_context.rs guards the WebRender stacking-context early-return on backdrop_filter.0.is_empty(); display_list/mod.rs adds BuilderForBoxFragment::build_backdrop_filter calling push_backdrop_filter before background paint.
• GAP-5: Per-app process isolation — requires Servo multi-process (constellation) architecture.

Update policy

The servo-weft branch is the working branch for WEFT-specific Servo patches. Upstream servo/servo changes are merged into it periodically.

To rebase onto a new upstream commit:

1. In the marcoallegretti/servo repo: git fetch upstream && git rebase upstream/main on servo-weft.
2. Force-push servo-weft.
3. Update Rev in this file to the new tip SHA.
4. Run cargo update -p servo in the WEFT OS workspace.
5. Confirm the compositor and shell tests still pass.

To submit patches upstream: open a PR from servo-weft (or a topic branch) to servo/servo.

Stylo fork

The Stylo CSS engine is a separate repo (servo/stylo) pinned at rev dca3934667dae76c49bb579b268c5eb142d09c6a in Cargo.toml. To patch it for WEFT-specific changes (e.g. enabling backdrop-filter):

1. Fork servo/stylo to marcoallegretti/stylo, create branch servo-weft.
2. Make changes on that branch.
3. Add to this fork's Cargo.toml workspace [patch] section:

[patch."https://github.com/servo/stylo"]
stylo = { git = "https://github.com/marcoallegretti/stylo", branch = "servo-weft" }
stylo_atoms = { git = "https://github.com/marcoallegretti/stylo", branch = "servo-weft" }
stylo_dom = { git = "https://github.com/marcoallegretti/stylo", branch = "servo-weft" }
stylo_malloc_size_of = { git = "https://github.com/marcoallegretti/stylo", branch = "servo-weft" }
stylo_static_prefs = { git = "https://github.com/marcoallegretti/stylo", branch = "servo-weft" }
stylo_traits = { git = "https://github.com/marcoallegretti/stylo", branch = "servo-weft" }
selectors = { git = "https://github.com/marcoallegretti/stylo", branch = "servo-weft" }
servo_arc = { git = "https://github.com/marcoallegretti/stylo", branch = "servo-weft" }

4. Run cargo update to resolve the new stylo deps.
5. Commit both the Cargo.toml and Cargo.lock changes to servo-weft.