[experiment] Consider WF of coroutine witness when proving outlives assumptions #143545

compiler-errors · 2025-07-06T21:58:20Z

This needs to be majorly cleaned up

Consider, for example:

use std::future::Future;

trait Client {
    type Connecting<'a>: Future + Send
    where
        Self: 'a;
    fn connect(&'_ self) -> Self::Connecting<'_>;
}

fn call_connect<C>(c: &'_ C) -> impl Future + Send
where
    C: Client + Send + Sync,
{
    async move { c.connect().await }
}

rustbot · 2025-07-06T21:58:24Z

r? @spastorino

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rustbot · 2025-07-06T21:58:27Z

Some changes occurred to the core trait solver

cc @rust-lang/initiative-trait-system-refactor

compiler-errors · 2025-07-06T21:58:36Z

@bors2 try @rust-timer queue

rust-bors · 2025-07-06T21:58:39Z

⌛ Trying commit 9613c58 with merge c9e8f2f…

To cancel the try build, run the command @bors2 try cancel.

[experiment] Consider WF of coroutine witness when proving outlives assumptions This needs to be majorly cleaned up --- cc #110338 Consider, for example: ```rust use std::future::Future; trait Client { type Connecting<'a>: Future + Send where Self: 'a; fn connect(&'_ self) -> Self::Connecting<'_>; } fn call_connect<C>(c: &'_ C) -> impl Future + Send where C: Client + Send + Sync, { async move { c.connect().await } } ```

compiler-errors · 2025-07-06T22:54:51Z

compiler/rustc_traits/src/coroutine_witnesses.rs

+        let region_assumptions = infcx.take_registered_region_assumptions();
+        let region_constraints = infcx.take_and_reset_region_constraints();
+        tcx.mk_outlives_from_iter(
+            make_query_region_constraints(


I need to eagerly resolve the assumptions here.

rust-bors · 2025-07-07T00:14:20Z

☀️ Try build successful (CI)
Build commit: c9e8f2f (c9e8f2fc63f9e854f5dc2b7f8dbffc5523b3138d, parent: de031bbcb161b0b7fc0eb16f77b02ce9fbdf4c9e)

rust-timer · 2025-07-07T09:28:28Z

Finished benchmarking commit (c9e8f2f): comparison URL.

Overall result: ❌✅ regressions and improvements - please read the text below

Benchmarking this pull request means it may be perf-sensitive – we'll automatically label it not fit for rolling up. You can override this, but we strongly advise not to, due to possible changes in compiler perf.

Next Steps: If you can justify the regressions found in this try perf run, please do so in sufficient writing along with @rustbot label: +perf-regression-triaged. If not, please fix the regressions and do another perf run. If its results are neutral or positive, the label will be automatically removed.

@bors rollup=never
@rustbot label: -S-waiting-on-perf +perf-regression

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	0.2%	[0.1%, 0.5%]	57
Regressions ❌ (secondary)	0.2%	[0.0%, 0.4%]	32
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.4%	[-1.0%, -0.0%]	8
All ❌✅ (primary)	0.2%	[0.1%, 0.5%]	57

Max RSS (memory usage)

Results (primary 1.1%, secondary -0.2%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	1.1%	[0.7%, 1.7%]	3
Regressions ❌ (secondary)	2.6%	[1.1%, 3.4%]	4
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-4.0%	[-4.7%, -2.8%]	3
All ❌✅ (primary)	1.1%	[0.7%, 1.7%]	3

Cycles

Results (primary 2.2%, secondary 0.7%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	2.2%	[2.2%, 2.2%]	1
Regressions ❌ (secondary)	2.7%	[2.1%, 3.0%]	6
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-5.4%	[-5.6%, -5.3%]	2
All ❌✅ (primary)	2.2%	[2.2%, 2.2%]	1

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 460.528s -> 463.281s (0.60%)
Artifact size: 372.13 MiB -> 371.71 MiB (-0.11%)

bors · 2025-07-09T23:41:13Z

☔ The latest upstream changes (presumably #143538) made this pull request unmergeable. Please resolve the merge conflicts.

compiler-errors · 2025-07-10T00:33:19Z

@bors2 try

rust-bors · 2025-07-10T00:33:23Z

⌛ Trying commit a7ec91c with merge 3c75d58…

To cancel the try build, run the command @bors2 try cancel.

[experiment] Consider WF of coroutine witness when proving outlives assumptions This needs to be majorly cleaned up --- cc #110338 Consider, for example: ```rust use std::future::Future; trait Client { type Connecting<'a>: Future + Send where Self: 'a; fn connect(&'_ self) -> Self::Connecting<'_>; } fn call_connect<C>(c: &'_ C) -> impl Future + Send where C: Client + Send + Sync, { async move { c.connect().await } } ```

rust-bors · 2025-07-10T02:50:05Z

☀️ Try build successful (CI)
Build commit: 3c75d58 (3c75d5844aa65b4aa19243ac44ceda49fe4e61ca, parent: e43d139a82620a268d3828a73e12a8679339e8f8)

compiler-errors · 2025-07-10T02:52:33Z

Don't expect this to fix any code, but I want to see whether it causes new issues.

@craterbot check

craterbot · 2025-07-10T02:53:03Z

👌 Experiment pr-143545 created and queued.
🤖 Automatically detected try build 3c75d58
🔍 You can check out the queue and this experiment's details.

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

craterbot · 2025-07-10T02:53:26Z

🚧 Experiment pr-143545 is now running

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

craterbot · 2025-07-11T05:20:46Z

🎉 Experiment pr-143545 is completed!
📊 6 regressed and 5 fixed (662328 total)
📰 Open the summary report.

⚠️ If you notice any spurious failure please add them to the denylist!
ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

rustbot · 2025-07-13T21:02:20Z

There are changes to the tidy tool.

cc @jieyouxu

…interiors

compiler-errors · 2025-07-14T01:33:56Z

@bors2 try @rust-timer queue

rust-timer · 2025-07-14T01:33:58Z

Awaiting bors try build completion.

@rustbot label: +S-waiting-on-perf

[experiment] Consider WF of coroutine witness when proving outlives assumptions This needs to be majorly cleaned up --- cc #110338 Consider, for example: ```rust use std::future::Future; trait Client { type Connecting<'a>: Future + Send where Self: 'a; fn connect(&'_ self) -> Self::Connecting<'_>; } fn call_connect<C>(c: &'_ C) -> impl Future + Send where C: Client + Send + Sync, { async move { c.connect().await } } ```

rust-bors · 2025-07-14T01:34:00Z

⌛ Trying commit 6999485 with merge fd967a6…

To cancel the try build, run the command @bors2 try cancel.

rustbot assigned spastorino Jul 6, 2025

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. WG-trait-system-refactor The Rustc Trait System Refactor Initiative (-Znext-solver) labels Jul 6, 2025

compiler-errors unassigned spastorino Jul 6, 2025

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rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Jul 6, 2025

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compiler-errors commented Jul 6, 2025

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rustbot added perf-regression Performance regression. and removed S-waiting-on-perf Status: Waiting on a perf run to be completed. labels Jul 7, 2025

compiler-errors force-pushed the coroutine-obl branch 2 times, most recently from 69dda47 to a7ec91c Compare July 10, 2025 00:33

craterbot added S-waiting-on-crater Status: Waiting on a crater run to be completed. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jul 10, 2025

craterbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-crater Status: Waiting on a crater run to be completed. labels Jul 11, 2025

compiler-errors mentioned this pull request Jul 13, 2025

Region constraint nits #143901

Open

compiler-errors force-pushed the coroutine-obl branch from a7ec91c to b5d740d Compare July 13, 2025 21:02

rustbot added A-tidy Area: The tidy tool T-bootstrap Relevant to the bootstrap subteam: Rust's build system (x.py and src/bootstrap) labels Jul 13, 2025

compiler-errors added 5 commits July 13, 2025 23:21

Add outlives to CoroutineWitnessTypes

0de911a

Deduce outlives obligations from WF of coroutine interior types

f370519

Consider outlives assumptions when proving auto traits for coroutine …

35e11ea

…interiors

Gate things properly

e5c394b

Add tests, some of them fail...

6999485

compiler-errors force-pushed the coroutine-obl branch from b5d740d to 6999485 Compare July 13, 2025 23:27

rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Jul 14, 2025

[experiment] Consider WF of coroutine witness when proving outlives assumptions #143545

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[experiment] Consider WF of coroutine witness when proving outlives assumptions #143545

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rust-timer commented Jul 7, 2025

Overall result: ❌✅ regressions and improvements - please read the text below

Instruction count

Max RSS (memory usage)

Cycles

Binary size

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