The static method ReadableStream.from is still waiting to be merged into the spec. I wrote an implementation to evaluate the design.

My observations:

• We don't actually expose any of the Iterator functionally outside of self-hosting and mostly just do everything in bytecode. This made interacting with iterators from C++ not really possible or at least more difficult
• To implement the cancelAlgorithm we would need to additionally expose GetMethod which is currently self-hosted (except for Proxies?). It's unfortunate this this doesn't just use IteratorClose, but I think this might be related to having the return value of the return() call available?

Wow, this is a really nice piece of work. '

To your second point, looking at the contract for an underlying source cancel promise, it's weird that unlike almost all the other cancel algorithms its producing a complicated IteratorResult value; perhaps the feedback here from us ought to just be "Use {Async}IteratorClose, and either have the promise be undefined or throw."

ReadableStream.from was merged into the spec proper yesterday. I've updated the patch and we are passing everything on https://wpt.live/streams/readable-streams/from.any.html.

Nice!

https://hg.mozilla.org/mozilla-central/rev/c9d9d8e3fae1

Is this something we should call out in the Fx117 relnotes?

I wonder all dev-doc-needed should also have relnote.

Release Note Request (optional, but appreciated)
[Why is this notable]: Normally I wouldn't call this really notable, but we seem to be documenting similar stuff in e.g. 115
[Affects Firefox for Android]: yes
[Suggested wording]: The ReadableStream.from allows creating a ReadableStream from an (async) iterable.
[Links (documentation, blog post, etc)]: We probably want to link to MDN when ready.

Added to the Fx117 relnotes.

FF117 MDN docs for this can be tracked in https://github.com/mdn/content/issues/28282

FF117 MDN docs work can be tracked in https://github.com/mdn/content/issues/28282