add IntoFuture trait and support for await #65244

seanmonstar · 2019-10-09T17:22:14Z

The async-await RFC mentions being able to await anything implementing IntoFuture. Somewhere along the way, it was left out.

Centril · 2019-10-09T17:26:54Z

r? @nikomatsakis cc @cramertj

seanmonstar · 2019-10-09T17:30:32Z

(My machine dies trying to compile rustc, so I'll be needing CI to tell me if I goofed a small thing. And I can add a tracking issue if accepted.)

src/librustc/hir/lowering/expr.rs

nikomatsakis

The code generally looks good to me -- though I feel like the test ought not to be passing. Let's see what travis says.

Anyway, the other question is whether we want to enable this. It'd be good to capture some of the motivation. The main thing I've heard (which I find persuasive) came from the async-finalizers blog post by @yoshuawuyts. The main reason I've heard for removing IntoFuture was basically "YAGNI" -- not sure if there were more motivations than that? (Maybe @withoutboats remembers?)

src/test/ui/async-await/await-into-future.rs

nikomatsakis · 2019-10-09T17:51:58Z

src/libcore/future/future.rs

@@ -99,6 +99,18 @@ pub trait Future {
    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output>;
 }

+/// Conversion into a `Future`.
+#[unstable(feature = "into_future", issue = "0")]


We should file a tracking issue, but let's hold off just a bit.

There should be a tracking issue before this gets merged, though, I think.

cramertj · 2019-10-09T17:56:19Z

I don't think it was forgotten about-- IntoFuture was intentionally removed from futures-rs a while back because the only things left that implemented it were tuple types. I'm not opposed to this PR at all; I don't know of any serious downsides to providing this functionality, aside from potentially yet another layer of indirection for error messages. However, I am curious to see what use-cases you have in mind for it!

nikomatsakis · 2019-10-09T17:58:38Z

@cramertj did you see the async-finalizers (since renamed to async-builders, I think) blog post I was referring to? That's at least one use case.

(I'd like to know if @seanmonstar had another use case in mind, though!)

seanmonstar · 2019-10-09T18:07:10Z

Yes, I've long had various builders in reqwest and hyper that I've previously felt would be nice if they could easily become futures, but they themselves aren't futures.

(My office internet is flaking hard, so might take a bit to update the PR.)

seanmonstar · 2019-12-27T21:56:56Z

@bors r+

bors · 2019-12-27T21:56:57Z

📌 Commit f35517e has been approved by seanmonstar

add IntoFuture trait and support for await The [async-await RFC](https://rust-lang.github.io/rfcs/2394-async_await.html#the-await-compiler-built-in) mentions being able to `await` anything implementing `IntoFuture`. Somewhere along the way, it was left out.

@ghost

Rollup of 15 pull requests Successful merges: - #65244 (add IntoFuture trait and support for await) - #67576 (reuse `capacity` variable in slice::repeat) - #67588 (Use NonNull in slice::Iter and slice::IterMut.) - #67594 (Update libc to 0.2.66) - #67602 (Use issue = "none" instead of "0" in intrinsics) - #67604 (Add Scalar::to_(u|i)16 methods) - #67617 (Remove `compiler_builtins_lib` documentation) - #67621 (Use the correct type for static qualifs) - #67629 (Remove redundant link texts) - #67632 (Convert collapsed to shortcut reference links) - #67633 (Update .mailmap) - #67635 (Document safety of Path casting) - #67654 (Add regression test for old NLL ICE) - #67659 (Stabilize the `matches!` macro) - #67664 (Fix some mailmap entries) Failed merges: r? @ghost

bors · 2019-12-28T03:37:00Z

⌛ Testing commit f35517e with merge 3a087ad...

bors · 2019-12-28T03:37:29Z

☔ The latest upstream changes (presumably #67670) made this pull request unmergeable. Please resolve the merge conflicts.

…crum Revert #65244 for performance reasons This reverts commit f35517e. Revert #65244 so we can see if it is the cause of the performance issue in #67706 cc #67644

@seanmonstar

Re-land "add IntoFuture trait and support for await" Testing the code from #65244 to see if the performance regressions are still there. #68606 and #68672 made perf optimizations that might interact with this change. If this lands, fixes #67982. cc @seanmonstar @jonas-schievink r? @cramertj

…akis Add core::future::IntoFuture This patch reintroduces the `core::future::IntoFuture` trait. However unlike earlier PRs this patch does not integrate it into the `async/.await` lowering since that lead to performance regressions. By introducing the trait separately from the integration, the integration PR can be more narrowly scoped, and people can start trying out the `IntoFuture` trait today. Thanks heaps! cc/ @rust-lang/wg-async-foundations ## References - Original PR adding `IntoFuture` rust-lang#65244 - Open issue to re-land `IntoFuture` (assigned to me) rust-lang#67982 - Tracking issue for `IntoFuture` rust-lang#67644

This is a reintroduction of the remaining parts from rust-lang#65244 that have not been relanded yet. Issues rust-langGH-67644, rust-langGH-67982

Reintroduce `into_future` in `.await` desugaring This is a reintroduction of the remaining parts from rust-lang#65244 that have not been relanded yet. This isn't quite ready to merge yet. The last attempt was reverting due to performance regressions, so we need to make sure this does not introduce those issues again. Issues rust-lang#67644, rust-lang#67982 /cc `@yoshuawuyts`

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add IntoFuture async-rs/async-std#259

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Prepare for 0.3.0 release in conjunction with Rust 1.39 rust-lang/futures-rs#1893

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seanmonstar force-pushed the into-future branch from a39ad71 to ad8c47c Compare October 9, 2019 18:52

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seanmonstar force-pushed the into-future branch from ad8c47c to 4b7100f Compare October 9, 2019 20:12

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seanmonstar force-pushed the into-future branch 2 times, most recently from bd3eb16 to 5e3d3bb Compare October 9, 2019 21:59

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seanmonstar force-pushed the into-future branch from 0b62bbe to 3ecc4f7 Compare December 27, 2019 19:49

core: add IntoFuture trait and support for await

f35517e

seanmonstar force-pushed the into-future branch from 3ecc4f7 to f35517e Compare December 27, 2019 19:56

bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-blocked Status: Marked as blocked ❌ on something else such as an RFC or other implementation work. labels Dec 27, 2019

oli-obk mentioned this pull request Dec 27, 2019

Rollup of 15 pull requests #67670

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bors added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Dec 28, 2019

bors merged commit f35517e into rust-lang:master Dec 28, 2019

Mark-Simulacrum mentioned this pull request Dec 29, 2019

Major async/await compiler performance regression #67706

Closed

jonas-schievink mentioned this pull request Dec 31, 2019

Nightly 2019-12-29 causes reached the type-length limit error in previously working code #67757

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wesleywiser mentioned this pull request Jan 1, 2020

Revert #65244 for performance reasons #67768

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tmandry mentioned this pull request Jan 7, 2020

Re-land "add IntoFuture trait and support for await" #67982

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tmandry mentioned this pull request Feb 3, 2020

Re-land "add IntoFuture trait and support for await" #68811

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yoshuawuyts mentioned this pull request May 22, 2020

Add core::future::IntoFuture #72459

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eholk mentioned this pull request Nov 9, 2021

Reintroduce into_future in .await desugaring #90737

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eholk added a commit to eholk/rust that referenced this pull request Nov 22, 2021

Reintroduce into_future in .await desugaring

dfa0db5

This is a reintroduction of the remaining parts from rust-lang#65244 that have not been relanded yet. Issues rust-langGH-67644, rust-langGH-67982

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add IntoFuture trait and support for await #65244

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