0.31-4

✨ What's New ✨

🕸️ A new WASM flavour: wasm2

uniffi-bindgen-react-native gains a second WASM target, built on the same player architecture as the Node.js runtime shipped in 0.31.0-3. There is no shim crate to generate and no per-library glue to compile: ubrn build wasm2 compiles your crate once for wasm32-unknown-unknown, and the bindgen reads the UniFFI metadata straight out of that same .wasm, so the second native-only cargo build disappears. The generated wrapper opens no module itself, which leaves it environment-neutral — the same bindings bundle for Node, browsers and React Native alike.

Getting started: your crate needs to be a cdylib, link the new uniffi-runtime-wasm helper crate, and enable the uniffi_core feature that drops Send + Sync on exported objects. ubrn build wasm2 checks all three up front rather than letting cargo fail later. The player runtime is published to npm as @ubjs/wasm.

• The player runtime, plus the uniffi-runtime-wasm helper crate consuming cdylibs link (#418).
• Post-link processing of the wasm module — staging, a growable function table for callback trampolines, and dead-export stripping — and the crate-manifest queries the build validates (#424).
• The Wasm2 ABI flavour in the bindgen, exporting PLAYER_DEFINITIONS and setNativeModule from the per-module wrapper, with a generated index.ts doing the opening (#425).
• The ubrn build wasm2 and ubrn generate wasm2 subcommands, aliased web2 (#426).
• The full fixture suite now runs against the flavour (#427) in CI (#428). As with the existing wasm flavour, the futures fixture is excluded: its TimerFuture wakes itself with std::thread::spawn, which single-threaded wasm32 cannot do.

Other new features

• bindings.typescript.forceAsync in uniffi.toml gives chosen types and functions an async/Promise surface in TypeScript without making them async in Rust, so call sites can be migrated to await ahead of any real off-main-thread work. Set it to true for the whole crate, or to a list of names. See the reference — in particular, it moves no work off the main thread (#408).
• bindings.typescript.strictTypeChecking drops the // @ts-nocheck header from generated files so tsc checks them (#408).
• Lifting and lowering now share a cursor instead of creating a DataView per value, which speeds up types made of many small reads and writes — large or deeply nested records, recursive enums — on every backend (#413).
• The supported uniffi-rs version is relaxed from =0.31.0 to =0.31, so 0.31.x point releases no longer need a matching release here (#431).

🦊 What's Changed

Memory leaks fixed

Four leaks affecting the N-API backend, present in 0.31.0-3. Upgrading is recommended for anyone making calls in a loop.

• The RustBuffer returned by an async call was never freed, leaking one buffer per async call returning a string, byte array, record or list. The wasm flavour was unaffected (#420).
• The N-API runtime allocated every RustBuffer argument twice and freed only one of the two, leaking a copy of each buffer passed into Rust — roughly 2.4 KB per frame. Lowered arguments are now library-owned rather than copied (#432). Thank you @1egoman!
• Callback trampolines were rebuilt on every call that marshalled a callback argument, instead of once per callback type as intended. rust_future_poll marshals its continuation on every poll, so every await of a uniffi async function paid this — each construction leaking a pinned napi_ref, a CallbackUserData, and a fresh ThreadsafeFunction libuv handle. Trampolines are now cached per callback type (#440).
• Callback interfaces implemented in TypeScript leaked their whole serialized return value on each invocation, for any method returning a record, enum, Vec, Option or byte array. #432 taught the argument path to adopt library-owned buffers; the callback-return path still copied, orphaning the original. String returns were never affected — their converter produces TextEncoder memory rather than a library allocation (#442).

Alongside those, the runtime now refuses to free a buffer it cannot prove the library owns, rather than falling back to guessing the capacity from byteLength. Generated code always marks the buffers it frees, so this is hardening rather than a user-visible fix (#441).

Fixes

• N-API: is_js_thread is now answered per callback rather than per process. Calling a library from a Node worker_threads worker — which is what Vitest and Jest do by default — hung on the first call, taking down worker.terminate() and process.exit() with it. Every async call was affected, not just calls with a callback of your own (#433, fixing #436). Thank you @stupside!
• Escape */ in generated TypeScript docstrings. TypeScript doesn't allow nested block comments, so a */ in a doc comment closed the docstring early and the rest was parsed as code, failing the build (#438). Thank you @liamiepops!
• Export the ./package.json subpath from the root package. The generated Android CMake resolves the package root with require.resolve('uniffi-bindgen-react-native/package.json'), which failed with ERR_PACKAGE_PATH_NOT_EXPORTED where Node enforces the exports map (#407, fixing #404). Thank you @DeyLak!
• Android: replace the deprecated TurboReactPackage with BaseReactPackage in the generated Kotlin and Java packages (#411, fixing #410). Thank you @ANAMASGARD!
• Emit opt-level = 3 rather than opt-level = "3" in the generated WASM template's release profile (#401). Thank you @MrCreativ3001!

CI

• The React Native compatibility matrix is now date-derived: React Native versions, create-react-native-library versions and runner images are tied together by date, covering the last 12 months of React Native. Per-PR checks run the latest versions only; the historical sweep runs nightly. This fixes the frequent build breakages caused by old React Native versions no longer building on macos-latest (#419).
• Node 24 in CI (#439).

⚠️ Breaking Changes

• The N-API RustBuffer fixes change the contract between the generated bindings and the runtime: regenerate your bindings and upgrade @ubjs/node together. A new runtime with old bindings, or the reverse, will not behave correctly (#420, #432).

Full Changelog: 0.31.0-3...0.31-4