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svelte-rs

A Svelte-style cross-platform desktop UI library in Rust — exploratory prototype.

The idea: bring Svelte 5's compilation philosophy to native desktop. Templates compile into pinpoint updates against a retained scene tree — no virtual DOM, no diffing, no rebuild at runtime. Target platforms: Windows / Linux / macOS / HarmonyOS NEXT.

let count = state(0);                          // $state
let double = derived(move || count.get() * 2); // $derived
effect(move || println!("{}", double.get()));  // $effect
count.set(1);                                  // precise trigger, no diff

Or the same thing in a .svelte single-file component — real Svelte template syntax, real Rust expressions (the compiler rewrites count += 1 into handle operations):

<script>
let count = $state(0i32);
let double = $derived(count * 2);
</script>

<text>Count: {count} · doubled = {double}</text>
<button style="bg:#ff3e00; fg:#fff" onclick={|| count += 1}>+1</button>
{#if count > 5}
  <text fg="#ff3e00">Past five!</text>
{/if}

Highlights

• Runes kernel in Rust — state / derived (writable) / effect / batch / untrack / context, push-pull three-state dirty marking, effect ownership tree.
• Two compiler frontends, one target — a view! proc-macro and a .svelte single-file-component compiler (build.rs integration) both emit calls to the same scene-tree binding primitives.
• Real CSS, compiled — a closed subset of actual CSS syntax (:hover, :root variables, nesting, inheritance) resolved at build time; zero runtime selector engine.
• Switchable render backends — CPU (tiny-skia + swash) and GPU (vello 0.9 / wgpu) behind one Painter trait; select per build, per env (SV_RENDERER), with automatic fallback.
• Scales to a million widgets — viewport virtualization (virtual_list) measured at 1,000,000 logical controls: p99 = 5.28 ms, 1% low = 174 fps, 28 MB working set (CPU backend, continuous-scroll worst case).

Quick start

cargo test                    # run the whole test suite
cargo run -p showcase         # feature tour (recommended first stop)
cargo run -p counter          # counter, view! macro route
cargo run -p counter-sfc      # counter, .svelte compiler route (UI in src/Counter.svelte)
cargo run -p showcase -- --png out.png  # render one frame offscreen, no window needed

If the checkout lives inside OneDrive or another synced folder, enable the commented-out target-dir in .cargo/config.toml to keep build artifacts out of the sync scope.

Documentation

The documentation center lives in docs/ — guides in English and 中文:

Guide
Getting started	Install, run the examples, repo tour
Architecture	Layers, data flow, why no VDOM
Reactivity	The runes kernel as a user guide
.svelte components	Template syntax, props, build integration
Styling	The compiled CSS subset
Render backends	Painter trait, CPU/vello, knobs
Performance	virtual_list, membench, measured numbers

Reference material (Chinese): design & ADRs · Svelte support matrix, 77 items · modern-CSS gap matrix, 91 items · research reports ×31

Repository layout

Path	What it is
crates/sv-reactive	Runes reactive kernel
crates/sv-ui	Retained scene tree + fine-grained binding primitives
crates/sv-macro	view! proc-macro frontend
crates/sv-compiler	.svelte single-file-component compiler frontend (+ sv check)
crates/sv-shell	winit window shell + CPU/vello renderers
crates/sv-vap · sv-pag · sv-lottie	Animation-format parsers (VAP / PAG / Lottie)
crates/sv-lsp	.svelte language server (LSP): live compiler diagnostics
crates/sv-arco-tokens	Arco Design tokens: palette algorithm port + global.less transliteration (Rust consts + :root CSS)
crates/sv-arco	Arco-style component library (.svelte components; A1 static set landed: Button/Tag/Badge/Divider/Alert/Typography/Link)
examples/	showcase · counter(-sfc) · todo-sfc · settings-sfc · input-demo · overlay-demo · membench · vap-gift · arco-gallery

Status

M0 exploration is complete: full loop from signal to pixels (CJK text, HiDPI, hit testing), .svelte compiler covering the main Svelte 5 syntax surface (43 of 77 matrix items ✅), dual render backends, and the million-widget virtualization result. This is a prototype — APIs churn, and several subsystems (layout, text shaping, frame pacing) are placeholders with planned replacements. See docs/DESIGN.md (Chinese) for the roadmap and ADRs.

Versioning & releases

Nothing is published to crates.io yet. Naming is settled (ADR-10 in docs/DESIGN.md: umbrella crate svelte-rs, sub-crates keep the sv-* prefix). Once published, the workspace ships all crates at the same version, in dependency order.

0.x policy: a minor bump (0.X.0) means breaking changes, a patch bump (0.0.X) is backwards compatible. Every breaking change documents its migration in CHANGELOG.md. All three breaking changes scheduled before 1.0 is even discussed have landed: the two template front-ends share a single compilation kernel (ADR-2 M1), the on: event directive has been removed in favor of Svelte 5's onclick={..} attribute form, and frame-pacing semantics (ADR-6) batches signal writes to the frame boundary. What remains before 1.0 is the first crates.io release plus a stabilization period.

MSRV is 1.88 — set by let-chains (if let ... && ...), not by edition 2024 — and pinned by a CI lane.

License

Dual-licensed: MIT OR Apache-2.0.