WASM

WASM defines a portable binary format for virtual machines running untrusted code in browsers and various other scenarios. Depending on the scenario, the host language may vary.

As such, uniffi-rs does not come with bindings generators "for WASM". This is the job for external uniffi-bindgen generators. e.g. Typescript, Kotlin.

However, the generated scaffolding needs to be configured for that WASM32 target.

Configuration

Configuring the Rust scaffolding ready for WASM binding generators is done by opting into features.

e.g.

[dependendencies]
uniffi = { version = "0.29.2", features = ["wasm-unstable-single-threaded"]}

Features

wasm-unstable-single-threaded

At time of writing, the state of threading in WASM and Rust support is still in flux.

Much of the ecosystem is built around gloo, web-sys and wasm-rayon.

Enabling the wasm-unstable-single-threaded feature opts out of the Send and Sync checks when building for wasm32 target architectures.

This feature only affects the wasm32 architecture.

Hint: running clippy on client code built for wasm32 may trigger a clippy warning when constructing Arcs.

The lint's remedy is either to: - make the object to Send and Sync, or - change from an Arc to an Rc.

As we are using this feature: - to allow Send and Sync, and - we can't use Rc for other targets

we can disable this warning for wasm32 only like so:

#[cfg_attr(target_arch = "wasm32", allow(clippy::arc_with_non_send_sync))]
fn new() -> Arc<Self> {
    Arc::new(Self {})
}

Note: as support for WASM threads evolves, this feature is likely to change or go away completely.