wasm-bindgen 0.2.122

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Created by brew bump

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Details

release notes

### Notices


Threading support now requires -Clink-arg=--export=__heap_base to be set

in RUSTFLAGS for nightly toolchains from 2026-05-06 onward, after

rust-lang/rust#156174

removed the implicit __heap_base/__data_end exports on wasm*

targets. Atomics CI, CLI reference tests, and the nodejs-threads,

raytrace-parallel, and wasm-audio-worklet examples have been

updated to pass --export=__heap_base explicitly. The flag is

backward-compatible with older nightlies.


-Cpanic=unwind on wasm targets now emits modern (exnref) exception

handling by default after

rust-lang/rust#156061,

and requires Node.js 22.22.3+ (for WebAssembly.JSTag). Legacy EH wasm

can still be produced on current nightlies by adding

-Cllvm-args=-wasm-use-legacy-eh to RUSTFLAGS; Node.js 20 may be

supported with legacy exception handling, with a tracking issue in

#5151.


Added


Implemented TryFromJsValue for Vec<T> where T: TryFromJsValue.

A JS value converts when it is a real Array (per Array.isArray)

and every element converts via T::try_from_js_value. This composes

recursively (Vec<Vec<String>>, Vec<Option<T>>) and works for any

T with a TryFromJsValue impl, including primitives, String,

JsValue, and JsCast types. Array-likes (objects with length and

numeric indices) are intentionally rejected to mirror the static ABI

representation used by js_value_vector_from_abi.


New extends_js_class and extends_js_namespace attributes on

exported structs to allow defining the parent js_class name when

it has been customized by js_name and the parent's own js_namespace

as well in turn. New validation is added at code generation time that

will now catch these cases instead of emitting invalid code. Example:
#[wasm_bindgen(js_name = "Animal", js_namespace = zoo)]
pub struct AnimalImpl { /* ... */ }

#[wasm_bindgen(
    extends = AnimalImpl,
    extends_js_class = "Animal",
    extends_js_namespace = zoo,
)]
pub struct DogImpl { /* ... */ }
#5154


Changed


When an exported struct uses js_namespace, the corresponding value

must now be repeated on every impl block. Previously the impl-side

defaults silently worked resulting in inconsistent emission. Example:
// Before:
#[wasm_bindgen(js_namespace = "default")]
pub struct Counter { /* ... */ }

#[wasm_bindgen]              // worked, but fragile
impl Counter { /* ... */ }

// After:
#[wasm_bindgen(js_namespace = "default")]
pub struct Counter { /* ... */ }

#[wasm_bindgen(js_namespace = "default")]   // now required
impl Counter { /* ... */ }
To ease this transition for js_namespace usage, diagnostic

messages now include hints for missing namespaces for easier

fixing.
#5154


Fixed


Fixed the descriptor interpreter panicking on Br and BrIf

instructions emitted by recent nightly compilers when building with

panic=unwind.

#5158


Emscripten output now works against vanilla upstream emscripten without

requiring a fork. Dependency tracking, HEAP_DATA_VIEW setup,

function-decl intrinsic inlining, catch-wrapper gating, and imported

global handling have all been corrected; ESM imports

(#[wasm_bindgen(module = "...")] and snippets) are emitted to a

sidecar library_bindgen.extern-pre.js consumers pass to emcc via

--extern-pre-js; namespaced exports (js_namespace = [...] on a

struct/impl) now attach to Module.<segments> instead of emitting

top-level export const (which emcc's library evaluator rejects);

the generated .d.ts for namespaced exports is now valid TypeScript

(mangled identifiers stay module-internal via declare class /

declare enum / declare function plus export { BindgenModule };

to mark the file as a module; no spurious unqualified Calc:

property on BindgenModule for namespaced items; namespace shapes

land as plain interface members (app: { math: { Calc: typeof app__math__Calc } };) instead of the previously-emitted export let app: { ... }; which was invalid TS1131 syntax inside an

interface body).

#5156


Fixed a duplicate phantom class being emitted for an exported struct

renamed via js_name (Rust ident != JS class name) and/or placed in a

js_namespace, when the struct crosses the boundary as a JsValue

(e.g. via .into()). The WrapInExportedClass / UnwrapExportedClass

imports were keyed by the Rust ident rather than the qualified JS name

that exported_classes is keyed by (a regression from #5154), so a

fresh empty class entry was minted and emitted alongside the real one,

with a free() referencing a nonexistent wasm export. Riding the

same release's #5154 wire-format bump, the now-vestigial rust_name

field is dropped from the schema and the namespace-qualified name is

no longer cached on AuxStruct, AuxEnum, or ExportedClass

(derived on demand from (name, js_namespace)), collapsing three

fallback chains that only papered over the pre-#5154 keying.
#5160

View the full release notes at https://github.com/wasm-bindgen/wasm-bindgen/releases/tag/0.2.122.

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