Free RustCallStatus pointer after every Rust call

[LautaroPetaccio]

Summary

Every synchronous call into Rust through makeRustCall leaks the call-status struct that gets passed in. Wrap the call site in try/finally and reclaim the pointer with freePointer.

Why this is a leak

createCallStatus calls ffi-rs's createPointer({ paramsType: [DataType_UniffiRustCallStatus], ... }). DataType_UniffiRustCallStatus does not set ffiTypeTag: DataType.StackStruct (only the inner error_buf field does), so ffi-rs takes the heap-allocation branch in get_value_pointer:

RsArgsValue::Object(val) => {
  if is_stack_struct {
    generate_c_struct(...)
  } else {
    Box::into_raw(Box::new(generate_c_struct(...))) as *mut c_void
  }
}

That produces two heap allocations: the struct itself (via generate_c_struct) and a wrapper Box<*mut c_void>. Neither is owned by JS. From the ffi-rs README: "JsExternal objects do NOT automatically free memory upon garbage collection. Use freePointer to free the pointer when it is no longer in use." restorePointer is read-only, and unwrapPointer only produces a new external around the inner pointer — neither reclaims the original allocation.

Net effect: every sync FFI call leaks roughly the size of UniffiRustCallStatus plus a pointer-sized wrapper. Method calls leak it twice (once for clonePointer, once for the actual call). Constructors, uniffiDestroy, and the FinalizationRegistry-driven free path each leak it once. For long-running or high-throughput consumers this is unbounded growth.

How the fix works

makeRustCall now wraps the call site in try/finally and calls freePointer on $callStatus in the finally block, using the same DataType_UniffiRustCallStatus paramsType and PointerType.RsPointer so ffi-rs takes the matching free path (free_rs_pointer_memory Object branch: dealloc the struct memory and reclaim the wrapper). The finally ensures the pointer is freed whether the Rust call returned normally, the call status indicated an error and uniffiCheckCallStatus threw, or any other exception propagated through the body.

[1egoman]

Makes sense, thanks!