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)

Cargo dependencies

The Servo deps are wired in crates/weft-servo-shell/Cargo.toml and crates/weft-app-shell/Cargo.toml under the servo-embed optional feature. They are off by default to avoid pulling the Servo monorepo (~1 GB) into every cargo check cycle.

Current Cargo.toml block (already committed):

[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

To 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:

• libglvnd-devel
• libopenssl-devel
• dbus-1-devel
• libudev-devel
• libxkbcommon-devel
• libwayland-devel

Install with: sudo zypper install -y libglvnd-devel libopenssl-devel dbus-1-devel libudev-devel libxkbcommon-devel libwayland-devel

Rendering approach

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

EGL path: 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 via surfman's eglSwapBuffers; the softbuffer blit is skipped. Mesa handles DMA-BUF buffer sharing with the compositor transparently.

Known limitations at this pin

• Wayland input events: not forwarded to Servo Resolved — keyboard and mouse events forwarded via webview.notify_input_event; key mapping in keyutils.rs.
• Wayland surface sharing: ZweftShellWindowV1 created with surface = null Resolved — ShellClient::connect_with_display(display_ptr, surface_ptr) uses Backend::from_foreign_display to share winit's wl_display connection; the winit wl_surface pointer is passed directly to create_window, associating the compositor shell slot with the actual rendered surface. ShellClient is now constructed inside resumed() after the winit window exists, not before the event loop. EGL path and per-frame event dispatch are unchanged. Protocol note: wayland-scanner 0.31 generates _type (not r#type) for the navigation_gesture event arg named type.
• WebGPU on Mesa: adapter may fail CTS — validation task, requires Mesa GPU hardware.
• CSS layout features: 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.
• Per-app process isolation: not implemented Resolved — each app runs in a separate weft-app-shell and weft-runtime OS process pair supervised by weft-appd. OS-level isolation does not require Servo's multi-process constellation architecture.
• SpiderMonkey sandbox: SpiderMonkey is not sandbox-isolated beyond process-level isolation. JIT-compiled JS runs with the same memory permissions as the Servo process. WEFT relies on SpiderMonkey's own security properties for the JavaScript execution boundary. See docs/security.md for the full bounded statement. Not addressed.

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" }

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