wasm-bindgen Files

Added

• Added OffscreenCanvas overloads for the WebGL texImage2D, texSubImage2D, texImage3D and texSubImage3D functions, matching the TexImageSource typedef in the WebGL specification. #5312

• Added --split-debug-info to the CLI. This option extracts the DWARF debug info to a separate *_bg.debug.wasm file. Use --debug-info-url to set the recorded URL for the debug info. #5279

• Added #[wasm_bindgen(experimental_generic_mono)] for imported functions, which binds a generic import once per monomorphisation instead of erasing its type parameters to JsValue. It can be applied to an individual import or to a whole extern "C" block, which every generic function in the block then inherits. Each instantiation gets its own descriptor, so arguments and return values are marshalled at their concrete types (a u32 crosses as a number, a String as a string) rather than being boxed. Trait bounds, where predicates (including higher-ranked ones), associated-type projections, lifetime parameters, argument-position impl Trait, raw callbacks with owned generic inputs and returns, async, catch, and slice_to_array are all supported; see the guide for the supported surface and the shapes that are rejected. The attribute is experimental and may change as it stabilizes. #5230 #5272 #5314

• #[wasm_bindgen(experimental_generic_mono)] now supports class-level generic parameters: an imported type that is itself generic (type Holder<T>), used as a method receiver (this: &Holder<T>), or as the return type of a constructor or self-returning static method (fn new<T>(value: T) -> Holder<T>). See Class-level generics in the guide. #5290

• A generic imported type used as a method receiver or a constructor's return type may now carry concrete generic arguments (this: &Holder<u32>, this: &Holder<u32, T>). The arguments are re-emitted as written, so the generated method hangs off impl Holder<u32> rather than the class's own parameter defaults. #5290

• Added experimental JSPI (JS Promise Integration) support: using it emits a compiler warning noting the experimental status. Supports #[wasm_bindgen(jspi)] on exports (sync or async), within which a #[wasm_bindgen(suspending)] import call can suspend to the JS event loop until its Promise settles. js_sys::futures::jspi_block_on_promise also suspends on any Promise inside a synchronous function, while spawn_local is context-aware: tasks spawned from within a JSPI context support synchronous JSPI suspensions throughout their call trees. Compatible with catch (rejections as Err), async, and panic=unwind. #5193

• Added a --ts-typed-array-buffers CLI flag to declare owned typed-array return values (e.g. Vec<u8>) as Uint8Array<ArrayBuffer> in generated TypeScript, since they are always copied into a fresh, non-shared ArrayBuffer. Requires TypeScript 5.7+. #5263

Changed

• Export shim symbols are now mangled with a per-crate hash, so identically named exports from different crates (or two versions of one crate) no longer fail the link with duplicate-symbol errors; the CLI restores the canonical names in the final module. Same-named #[wasm_bindgen(private)] structs/enums now coexist (numbered Name, Name2, ... internally in the generated bindings), while genuinely conflicting public exports are reported as a wasm-bindgen error instead of a wasm-ld failure. Requires matching wasm-bindgen and CLI versions (schema bump). #2247

• Setting js_namespace on both an extern "C" block and an item inside it is now a hard error. Nested paths must be written in a single attribute, e.g. js_namespace = ["a", "b"]. The previous behavior silently dropped the block-level namespace. #4324

• Changed WebGPU setImmediates APIs to take immutable u8 slice. #5289

• Changed Web Bluetooth writeValue / writeValueWithResponse / writeValueWithoutResponse and WebUSB controlTransferOut / transferOut / isochronousTransferOut APIs to take immutable u8 slices. #5309

• Emscripten glue no longer reads wasmExports['name'] inline inside inner functions. It now references the asmjs-mangled identifiers emcc's own top-level assignWasmExports receiving code binds for every wasm export (e.g. ___wbindgen_malloc, ___wbindgen_externrefs), which are the canonical DCE-graph pairs: wasm-metadce keeps exactly the exports the included glue uses (previously internal exports and the externref table could be stripped or left unrenamed by the import/export minifier at -O2, breaking at runtime). Hoisted classes are now emitted as =-prefixed string value snippets so jsifier declares them as export var Class = class Class {...} instead of an export class declaration, which crashes emcc's acorn-optimizer under -sMODULARIZE=instance.

Fixed

• The thread-bootstrap transform is now skipped in Emscripten mode, where the Emscripten runtime owns pthread startup and TLS. It previously ran on any module with shared memory and aborted the build (failed to find __wasm_init_tls), since Emscripten's linker had already consumed the synthetic symbols it looks for. #5315

• Fixed conflicting deprecation messages on web-sys dictionary fields that are themselves deprecated: the deprecated builder-style method no longer points at an equally-deprecated setter, and the WebAuthn fields removed from the specification (such as PublicKeyCredentialRpEntity's icon) now state why they are deprecated. #5302

• #[wasm_bindgen] on a struct now reports an actionable error when the path to the wasm_bindgen crate cannot be resolved (e.g. when wasm-bindgen is only a transitive dependency through web-sys), instead of a confusing recursion limit error. #5295

• Fixed js_namespace exports missing from the bundler target's entry module re-export list, making namespaces unreachable when importing the package. #5267

• The CLI now reports an actionable error when the __wasm_bindgen_unstable custom section is missing from a module that still contains wasm-bindgen shims (e.g. stripped by llvm-objcopy --strip-all, which removes all custom sections since LLVM 23), instead of the confusing import of `X` doesn't have an adapter listed. #5268

• The generated &T handle conversions (IntoWasmAbi/OptionIntoWasmAbi) for an imported type with lifetime parameters (type Holder<'a, T>) no longer reuse 'a for the reference itself. Previously the impl header declared only a fresh 'a plus the type's type parameters, so a type whose lifetime was not literally named 'a failed with E0261 against generated code, and one that was named 'a had its lifetime forced to unify with the borrow of &self — surfacing as E0521 whenever a generic method also had to resolve through the same impl. #5290

• An inline lifetime bound on a generic import (fn f<'a: 'b, 'b, T>(..)) is no longer dropped from the generated wrapper. Previously the bound was lost while the generated shim still declared it, so calling the import failed with "lifetime may not live long enough" reported against generated code. #5290

• A type-parameter default on a #[wasm_bindgen(experimental_generic_mono)] import is no longer silently ignored. It has no meaning there (every instantiation gets its own shim, so there is no single one to default) and rustc's own invalid_type_param_default lint cannot see it, since nothing of the original signature survives expansion; it is now rejected with the same defaults for generic parameters are not allowed here diagnostic rustc gives. Defaults on the type-erasure generic path are unaffected, where they remain meaningful. #5290

• Fix js-sys wasm64 build with atomics feature. #5274

• Declare initSync in the generated TypeScript definitions for --target no-modules, matching the wasm_bindgen.initSync function that the JS output already exposes. #5284

• Removed the last panicking code paths from externref table management: RefCell::borrow_mut() embedded panic location data (including the source path string) in .rodata of optimized builds, which not even wasm-opt could remove. #5292

• Fix --no-modules-global being ignored: the custom global name is now used for the generated JS binding and TypeScript declarations, and the name is validated as a JS identifier. #5286