Stream trait and related issues

[nikomatsakis]

Summary

In the context of the Async Foundations group, @nellshamrell has been drafting an RFC to stabilize the Stream trait. See e.g. rust-lang/wg-async#15 for the latest round of edits. While the actual content of the RFC is perhaps more libs than lang (introducing a trait), the choice of whether or not to introduce this trait touches on a number of lang issues, particularly around forwards compatibility, and I thought it would be good to discuss as a group.

Some of the issues I thought particularly relevant:

• Method dispatch ambiguity issues around migrating extension methods from futures crate to the stdlib (a common scenario that also applies to e.g. itertools for iterators)
• Coherence issues if we attempted to bridge a Stream trait with a future LendingStream (a.k.a., "streaming stream" or "attached stream") trait
• The possibility of generator syntax and potential compatibility issues that may arise there

cc @rust-lang/wg-async-foundations @sfackler

Background reading

Draft RFC: rust-lang/wg-async#15

About this issue

This issue corresponds to a lang-team design meeting proposal. It corresponds
to a possible topic of discussion that may be scheduled for deeper discussion
during one of our design meetings.

[nikomatsakis]

We were thinking of scheduling this for Aug 12 -- cc @withoutboats @nellshamrell @cramertj and @yoshuawuyts are y'all available on that date for the lang team design slot? (And others, those are folks who expressed interest to me in the past...)

[yoshuawuyts]

@nikomatsakis yes, that works for me!

[nellshamrell]

Works for me!

[nikomatsakis]

Scheduled: calendar event

[cramertj]

Yes, I'll be there!

[nikomatsakis]

Hmm, so I think we ought to postpone this by a week. In light of the Mozilla layoffs there is an important meeting that I have to attend that conflicts with this slot.

[nikomatsakis]

I took the liberty of moving calendar invite to Aug 19.

[LucioFranco]

That cal event shows may 13th? Just to confirm this is aug 18 at 1p eastern time?

[tmandry]

Looks like this was bumped again to next week.

[nikomatsakis]

Minutes posted: https://github.com/rust-lang/lang-team/blob/master/design-meeting-minutes/2020-08-26-stream-trait.md