I wonder if reference types could lift our requirement to manage references to JS closures manually?

With externrefs, the host gives Wasm limited access to host objects, but the host also needs to know when Wasm is finished with those objects, so it can clean them up. That clean up might involve closing a file handle or simply deallocating memory.

This means that JS closures should be passed to the Swift code as externref. Deallocating all references to externref would deallocate the closure on the JS side.

Reference types are now available in all browsers except Safari, and in the latter case they seem to only be hidden behind JSC_useWebAssemblyReferences flag. The only question is externref support in our toolchain...

Doesn't look like LLVM had much progress in that direction? 🤔 Also see WebAssembly/tool-conventions#122