Re: [whatwg/streams] Interesting edge case... queueMicrotask and desiredSize in start algorithm (Issue #1362)

MattiasBuelens left a comment (whatwg/streams#1362)

Correct, the call to `reader.read()` happens first.
```javascript
const rs = new ReadableStream({
  start(c) { queueMicrotask(/* ... */) },
  pull(c) { /* ... */ }
}, { highWaterMark: 1 });

const reader = rs.getReader();
const readPromise = reader.read(); // <<< happens synchronously
console.log(await readPromise);
```
This adds a read request to `reader.[[readRequests]]`, so the first call to `controller.enqueue()` will immediately fulfill that request and bypass `stream.[[queue]]` (see [step 3 of ReadableStreamDefaultControllerEnqueue](https://streams.spec.whatwg.org/#readable-stream-default-controller-enqueue)). Hence, the desired size remains unchanged.

If you run the same code without the `queueMicrotask`, then the call to `controller.enqueue()` happens before the first `reader.read()`. Hence, the chunk ends up in the queue, and the desired size decreases. When `reader.read()` is called, it is fulfilled immediately from the queue.

I hope that explains it?

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