feat(ops): op2 support for buffers in async ops

[mmastrac]

Supports owned buffers in and out:

#[op2] #[buffer] async fn(#[buffer] input: JsSlice) -> JsSlice {}
#[op2] #[buffer] async fn(#[buffer] input: JsSlice) -> Vec<u8> {}
#[op2] #[buffer] async fn(#[buffer] input: JsSlice) -> Box<[u8]> {}

[bartlomieju]

I know it's late, but... it's somewhat strange that we put #[buffer] before function definition. I'm sure it would be now a lot of work to change, but this would be lovely:

#[op2(async, core)]
async fn op_async_buffer(#[buffer] input: JsBuffer) ->   #[buffer] JsBuffer {
    input
  }

Similarly for serde:

#[op2(core)]
fn op_foo(#[smi] rid: ResourceId) -> #[serde] SomeStruct {}

[mmastrac]

I think this is just an unfortunate side-effect of Rust syntax. There are no return-position attributes (I'll double-check).

[mmastrac]

Yeah, so there are no attributes supported in the return position. What about this?

#[returns(buffer)] fn op...

[bartlomieju]

Alright, not a big deal. It's more of a nitpick. We can revisit it some time in the future. Let's keep pushing with the current impl

[bartlomieju]

LGTM!