rust-wasm-geo

name	rust-wasm-geo
description	Rust/WASM geo for FixMyBerlin FMC geo-heavy React apps: when to leave Turf for WASM, crate selection (geo, rstar, fast_paths, osm-reader, i_overlay, …), wasm-bindgen boundaries, and Vite integration for SPAs and TanStack Start. Use when adding WASM geo crates, profiling slow Turf, OSM/routing/isochrones, spatial indexes, or wiring wasm-pack into Vite.
disable-model-invocation	true

Rust / WASM geo

Default stack context: tech-stack skill. This skill covers Rust/WASM geo only.

When to apply

• Turf or JS geometry is too slow (profile first — main-thread blocking > ~100ms)
• OSM parsing, map model build, isochrones, spatial indexes, graph routing
• Thousands of features, repeated geometry ops, or polygon booleans at scale
• Adding or reviewing a wasm-pack crate, wasm.ts boundary, or Vite WASM plugins

Stay on Turf (JS) for single-feature ops on small GeoJSON and interactive editing feedback during prototyping.

Turf vs Rust/WASM

Stay on Turf (JS)	Add Rust/WASM
Single-feature ops on small GeoJSON	Thousands of features, repeated ops, or graph routing
Interactive editing feedback	OSM parsing, map model build, isochrones, spatial indexes
Prototyping	Main-thread blocking > ~100ms (profile first)

Batch geometry on large arrays (not routing/OSM): geoarrow-wasm instead of rolling your own.

Crate selection (quick)

Need	Crate
Geometry / GeoJSON	geo, geojson
Spatial index	rstar
Road routing	fast_paths
Graph algorithms	petgraph
OSM → graph	osm-reader (a-b-street fork)
Snap traces to roads	route-snapper-graph
Polygon booleans	i_overlay (see a-b-street/utils)
Contours / isolines	contour
Serialized map models	bincode + serde
Vector file I/O	flatgeobuf, geozero

Per-crate usage notes and WASM dependency versions: crates-and-packages.md.

Project structure

One crate per app, named for what it computes (geo-isochrone, route-buffer, …).

app/
├── wasm/
│   └── geo-isochrone/          # Rust crate (wasm-pack output → pkg/)
│       ├── Cargo.toml
│       └── src/
│           ├── lib.rs          # #[wasm_bindgen] surface only
│           └── isochrone.rs    # pure geo logic
└── src/
    └── features/isochrone/
        ├── wasm.ts             # sole JS import of pkg — React never imports pkg directly
        └── useIsochrone.ts     # React hook / Query wrapper

• lib.rs = #[wasm_bindgen] exports; inner modules = pure geo logic (testable without WASM).
• JS boundary: wrap exports in wasm.ts. Pass GeoJSON strings or bincode Uint8Array — not hand-built JS objects.
• State split: durable compute state in Rust; UI state in React (Zustand / URL / local useState).

WASM stack (Cargo)

Crate	Role
wasm-bindgen	JS ↔ Rust boundary
serde-wasm-bindgen	Serialize/deserialize across boundary
wasm-bindgen-futures	Async exports
console_error_panic_hook	Readable panics in devtools
getrandom with features = ["js"]	RNG in browser
web-time	Time in WASM

Build: wasm-pack (--target web), vite-plugin-wasm, target wasm32-unknown-unknown.

Reference setups: a-b-street/ltn, a-b-street/15m, a-b-street/utils.

Docs when stuck: wasm-bindgen book, geo on docs.rs.

App integration

App type	Guide
Vite SPA (no Start)	vite-spa-integration.md
TanStack Start	tanstack-start-integration.md

Both: dynamic-import WASM from wasm.ts only; never top-level import of .wasm in shared modules that may load on the server.

Non-negotiable rules

Topic	Rule
React imports	Components/hooks import wasm.ts only — never pkg/ or raw .wasm
Boundary types	GeoJSON as string or bincode Uint8Array; validate with Zod on the JS side after parse
Coordinates	WGS84, [lng, lat] at all API boundaries
Server modules	No WASM init in *.server.ts, server loaders, or createServerFn handlers
SSR	WASM runs client-only; lazy-init after hydration (see Start guide for route ssr)
Turf fallback	Keep Turf for small/interactive paths until profiling proves WASM is needed

Related skills

Topic	Skill
Map React API, layers, events	React Map GL docs (load when touching maps)
Route SSR, loaders, layout	tanstack-start-conventions
Client UI state around map tools	zustand-state-management
useEffect / map listeners	react-dev