RPC: Simple objects with only value types as keys and values should stay as value types

[tv42]

What versions & operating system are you using?

wrangler 4.25.0, node v24.3.0, Linux NixOS 25.05

Please provide a link to a minimal reproduction

No response

Describe the Bug

I would have expected this RPC method:

  hello(): { greeting: string } {
    return { greeting: "Hello" };
  }

to result in a signature of Promise<{ greeting: string }>.

Instead, it becomes Promise<{ greeting: string }> & Disposable.

There's nothing to dispose there! This seems like unnecessary overhead, and complicating what should have been a simple case.

Please provide any relevant error logs

No response

[tv42]

This seems overly simplistic:

https://github.com/cloudflare/workerd/blob/ae1225b767704ecd5dd63593b6a56c0f47693e3d/types/defines/rpc.d.ts#L115

type MaybeDisposable<T> = T extends object ? Disposable : unknown;

[kentonv]

No, this is correct. Any time an RPC method returns an object, the system automatically adds a disposer to it.

This is necessary because the RPC system does not know the types, so it does not know if the RPC might sometimes return an object containing stubs. It can only see whether the result actually contains stubs, for any particular call. But you might have an RPC that sometimes returns an object containing stubs, and sometimes doesn't. It's bad if the result is only sometimes disposable, because if you store the result into a using-declared variable, and it isn't disposable, an exception will be thrown.

So we are stuck with the rule that results always get a disposer added (unless it's a primitive, in which case that's not possible).