Only compute `specializes` query if (min)specialization is enabled in the crate of the specializing impl #126139

compiler-errors · 2024-06-07T20:13:48Z

Fixes (after backport) #125197

What

#122791 makes it so that inductive cycles are no longer hard errors. That means that when we are testing, for example, whether these impls overlap:

impl PartialEq<Self> for AnyId {
    fn eq(&self, _: &Self) -> bool {
        todo!()
    }
}

impl<T: Identifier> PartialEq<T> for AnyId {
    fn eq(&self, _: &T) -> bool {
        todo!()
    }
}

...given...

pub trait Identifier: Display   'static {}

impl<T> Identifier for T where T: PartialEq   Display   'static {}

Then we try to see if the second impl holds given T = AnyId. That requires AnyId: Identifier, which requires that AnyId: PartialEq, which is satisfied by these two impl candidates... The PartialEq<T> impl is a cycle, and we used to winnow it when we used to treat inductive cycles as errors.

However, now that we don't winnow it, this means that we now try calling candidate_should_be_dropped_in_favor_of, which tries to check whether one of the impls specializes the other: the specializes query. In that query, we currently bail early if the impl is local.

However, in a foreign crate, we try to compute if the two impls specialize each other by doing trait solving. This may itself lead to the same situation where we call specializes, which will lead to a query cycle.

How does this fix the problem

We now record whether specialization is enabled in foreign crates, and extend this early-return behavior to foreign impls too. This means that we can only encounter these cycles if we truly have a specializing impl from a crate with specialization enabled.

r? @oli-obk or @lcnr

…ate of the specialized impl

compiler-errors · 2024-06-07T20:14:04Z

@bors try @rust-timer queue

Only compute `specializes` query if (min)specialization is enabled in the crate of the specializing impl Fixes (after backport) rust-lang#125197 ### What rust-lang#122791 makes it so that inductive cycles are no longer hard errors. That means that when we are testing, for example, whether these impls overlap: ```rust impl PartialEq<Self> for AnyId { fn eq(&self, _: &Self) -> bool { todo!() } } impl<T: Identifier> PartialEq<T> for AnyId { fn eq(&self, _: &T) -> bool { todo!() } } ``` ...given... ```rust pub trait Identifier: Display 'static {} impl<T> Identifier for T where T: PartialEq Display 'static {} ``` Then we try to see if the second impl holds given `T = AnyId`. That requires `AnyId: Identifier`, which requires that `AnyId: PartialEq`, which is satisfied by these two impl candidates... The `PartialEq<T>` impl is a cycle, and we used to winnow it when we used to treat inductive cycles as errors. However, now that we don't winnow it, this means that we *now* try calling `candidate_should_be_dropped_in_favor_of`, which tries to check whether one of the impls specializes the other: the `specializes` query. In that query, we currently bail early if the impl is local: However, in a foreign crate, we try to compute if the two impls specialize each other by doing trait solving. This may itself lead to the same situation where we call `specializes`, which will lead to a query cycle. ### How does this fix the problem We now record whether specialization is enabled in foreign crates, and extend this early-return behavior to foreign impls too. This means that we can only encounter these cycles if we truly have a specializing impl from a crate with specialization enabled. ----- r? `@oli-obk` or `@lcnr`

bors · 2024-06-07T20:15:15Z

⌛ Trying commit 4b188d9 with merge 20182a9...

bors · 2024-06-07T21:48:22Z

☀️ Try build successful - checks-actions
Build commit: 20182a9 (20182a9ce3a4c9bba5a4d4df53c3b8777f2006cc)

rust-timer · 2024-06-07T22:50:47Z

Finished benchmarking commit (20182a9): comparison URL.

Overall result: ❌ regressions - no action needed

Benchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up. While you can manually mark this PR as fit for rollup, we strongly recommend not doing so since this PR may lead to changes in compiler perf.

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

Instruction count

This is a highly reliable metric that was used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	0.1%	[0.1%, 0.1%]	3
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

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

Cycles

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

Binary size

Results (secondary 0.0%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	0.0%	[0.0%, 0.0%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Bootstrap: missing data
Artifact size: 319.56 MiB -> 318.87 MiB (-0.21%)

lcnr · 2024-06-10T08:25:38Z

@bors r

bors · 2024-06-10T08:25:41Z

📌 Commit 4b188d9 has been approved by lcnr

It is now in the queue for this repository.

lqd · 2024-06-10T09:05:42Z

As 1.79 artifacts are being prepared right now, this PR could be stable-nominated in the future. Maybe we'll just keep a look at open issues to see whether people encounter #125197 or similar in the wild. There wasn't many crater regressions (nor did it seem issues were opened about this on nightly?), and maybe a stable backport won't be needed.

bors · 2024-06-11T07:01:21Z

⌛ Testing commit 4b188d9 with merge 336e6ab...

bors · 2024-06-11T09:10:26Z

☀️ Test successful - checks-actions
Approved by: lcnr
Pushing 336e6ab to master...

rust-timer · 2024-06-11T10:26:20Z

Finished benchmarking commit (336e6ab): comparison URL.

Overall result: no relevant changes - no action needed

@rustbot label: -perf-regression

Instruction count

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

Max RSS (memory usage)

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

Cycles

Results (secondary -4.8%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-4.8%	[-6.4%, -2.2%]	6
All ❌✅ (primary)	-	-	0

Binary size

Results (secondary 0.0%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	0.0%	[0.0%, 0.0%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Bootstrap: 677.913s -> 675.77s (-0.32%)
Artifact size: 320.07 MiB -> 319.45 MiB (-0.19%)

apiraino · 2024-06-20T14:21:34Z

Beta backport accepted as per compiler team on Zulip. A backport PR will be authored by the release team at the end of the current development cycle.

@rustbot label beta-accepted

apiraino · 2024-06-20T14:46:52Z

Also suitable for a stable backport in case a point release is planned.

@rustbot label stable-accepted

cuviper · 2024-06-21T00:48:48Z

Adding the nomination so it comes up in our queries.

@rustbot label stable-nominated

[beta] backports - Only compute `specializes` query if (min)specialization is enabled in the crate of the specializing impl rust-lang#126139 - Add pub struct with allow(dead_code) into worklist rust-lang#126315 - ci: Update centos:7 to use vault repos rust-lang#126352 r? cuviper

cuviper · 2024-08-01T16:45:03Z

Clearing stable backport labels since we didn't ship a 1.79 point release, and this is already in current stable 1.80.0.

@rustbot label -stable-nominated -stable-accepted

compiler-errors added 2 commits June 7, 2024 14:59

Failing test

1653a2d

Only compute specializes query if specialization is enabled in the cr…

4b188d9

…ate of the specialized impl

rustbot assigned oli-obk Jun 7, 2024

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. labels Jun 7, 2024

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rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Jun 7, 2024

compiler-errors added the beta-nominated Nominated for backporting to the compiler in the beta channel. label Jun 7, 2024

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rustbot removed the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Jun 7, 2024

rust-lang deleted a comment Jun 7, 2024

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-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jun 10, 2024

bors added the merged-by-bors This PR was explicitly merged by bors. label Jun 11, 2024

bors merged commit 336e6ab into rust-lang:master Jun 11, 2024
7 checks passed

rustbot added this to the 1.81.0 milestone Jun 11, 2024

compiler-errors deleted the specializes branch June 11, 2024 12:06

rustbot added the beta-accepted Accepted for backporting to the compiler in the beta channel. label Jun 20, 2024

rustbot added the stable-accepted Accepted for backporting to the compiler in the stable channel. label Jun 20, 2024

rustbot added the stable-nominated Nominated for backporting to the compiler in the stable channel. label Jun 21, 2024

cuviper mentioned this pull request Jun 21, 2024

[beta] backports #126772

Merged

cuviper modified the milestones: 1.81.0, 1.80.0 Jun 21, 2024

cuviper removed the beta-nominated Nominated for backporting to the compiler in the beta channel. label Jun 21, 2024

rustbot removed stable-nominated Nominated for backporting to the compiler in the stable channel. stable-accepted Accepted for backporting to the compiler in the stable channel. labels Aug 1, 2024

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Only compute `specializes` query if (min)specialization is enabled in the crate of the specializing impl #126139

Only compute `specializes` query if (min)specialization is enabled in the crate of the specializing impl #126139

compiler-errors commented Jun 7, 2024 •

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cuviper commented Aug 1, 2024

Only compute specializes query if (min)specialization is enabled in the crate of the specializing impl #126139

Only compute specializes query if (min)specialization is enabled in the crate of the specializing impl #126139

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compiler-errors commented Jun 7, 2024 • edited Loading

What

How does this fix the problem

compiler-errors commented Jun 7, 2024

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rust-timer commented Jun 7, 2024

Overall result: ❌ regressions - no action needed

lcnr commented Jun 10, 2024

bors commented Jun 10, 2024

lqd commented Jun 10, 2024 • edited Loading

bors commented Jun 11, 2024

bors commented Jun 11, 2024

rust-timer commented Jun 11, 2024

Overall result: no relevant changes - no action needed

apiraino commented Jun 20, 2024

apiraino commented Jun 20, 2024

cuviper commented Jun 21, 2024

cuviper commented Aug 1, 2024

Only compute `specializes` query if (min)specialization is enabled in the crate of the specializing impl #126139

Only compute `specializes` query if (min)specialization is enabled in the crate of the specializing impl #126139

compiler-errors commented Jun 7, 2024 •

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