wasm-bindgen Files

Added

• Added the maxAge attribute to the CookieInit dictionary in web-sys, matching the current Cookie Store API specification. #5169

• The js-sys futures codegen opt-in can now also be enabled via the WASM_BINDGEN_USE_JS_SYS=1 environment variable, in addition to --cfg=wasm_bindgen_use_js_sys. This works on stable when --target is in use, where Cargo does not propagate the cfg to host proc-macros. #5164

Changed

• JsOption<T> now treats only undefined as empty, aligning it with TypeScript's strict T | undefined semantics and with Option<T>'s wire shape (None ↔ undefined). Previously is_empty, as_option, into_option, unwrap, expect, unwrap_or_default, and unwrap_or_else treated both null and undefined as absent; JS null is now a distinct present value. The impl<T> UpcastFrom<Null> for JsOption<T> is removed (Undefined still models absence), and the Debug/Display absent placeholder changed from "null" to "undefined". Code relying on null → None should return undefined from the JS side, or check explicitly with val.as_option().filter(|v| !v.is_null()). #5170

Fixed

• Removed invalid js_sys::Array<T> to js_sys::ArrayTuple<(...)> upcasts. ArrayTuple encodes a fixed tuple arity, while a plain JavaScript array does not prove that arity statically.

• Fixed incorrect variance in &mut reference upcasting. &mut T upcasts were covariant in the pointee, so a &mut T could be widened to a &mut of a supertype and used to write back a value the original type would not accept, leaving a reference whose static type no longer matches the value it points to. Mutable references are now invariant in their pointee: &mut T only upcasts to &mut Target when both Target: UpcastFrom<T> and T: UpcastFrom<Target> hold. This rejects the invalid widening but is a breaking change for callers that relied on widening &mut references. #5176

• Fixed WASI targets (wasm32-wasip1/wasm32-wasip2) emitting unresolved __wbindgen_placeholder__ imports, which broke component linking. The codegen and runtime gates now exclude target_os = "wasi" (restoring the pre-0.2.115 stub behavior), including the panic = "unwind" paths in wasm-bindgen-futures. #5175

• Fixed a panic ("Unhandled load width 8") in the descriptor interpreter when processing -Cinstrument-coverage-instrumented modules, unblocking cargo llvm-cov --target wasm32-unknown-unknown for crates whose describe helpers get instrumented. #5179

• Fixed main silently never running on wasm64 for bin crates. #5181