Re: [whatwg/streams] Piping to writable streams with HWM 0? (#1158)

> Is this different from just making HWM 0 equivalent to HWM 1?

I believe it's different in the case where the queue total size is between 0 and 1. But the fundamental issue where it causes a chunk to end up in the queue remains; see below.

> Okay, then it's back to the explicit controller.releaseBackpressure(). 

I was hoping there'd be some way to get the benefit here, without a new API, and with some way of "fixing" HWM = 0 so that it's less of a footgun and more useful.

But going back to the description of the desired behavior,

> With HWM = 0, the stream is asking not to put anything its queue, except for the case where it wants a chunk. Here, most of the time writer.ready will be pending. When the sink eventually wants a chunk, writer.ready temporarily becomes resolved and waits for a chunk to be written. Once that happens, writer.ready becomes pending again.

I guess we might need something different after all. If we try to use the HWM, we're intricately tied to the queue; the only way to switch between "not ready" and "wants a chunk" mode is by manipulating the contents of the queue, presumably by dropping it from containing a chunk to not containing a chunk. But that means the queue must contain a chunk during the "not ready" state, which is what we want to avoid!

So I am convinced that we cannot do anything just by tweaking the HWM/queue comparison mechanism.

That leaves two options:

- Explicit method; or
- `readyWhenNotWriting`

How do these compare in expressiveness? At first I thought the explicit method was more expressive, since you could combine it with any arbitrary HWM. But I wonder if that's actually true... does it make sense to use it with non-0 HWMs? How do each compare for realistic use cases?

It almost feels like `readyWhenNotWriting` is just a totally alternate kind of queuing strategy, separate from a size-based one?

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