[CRATER] Require equality for symmetric LUB coercion #150408

jackh726 · 2025-12-26T21:29:10Z

Ensures that these both error:

struct Wrap3<T: ?Sized>(T);

impl<'b, T: ?Sized + std::marker::Unsize<U> + std::ops::CoerceUnsized<U>, U: ?Sized>
    std::ops::CoerceUnsized<Wrap3<U>> for Wrap3<T> {}

type I = Wrap3<Inner>;
type J = Wrap3<dyn Dynable + Send>;
type K = Wrap3<dyn Dynable>;

// LUB is `J` on nightly
match 0 {
    0 => &Wrap3(Inner)      as &I,
    1 => &Wrap3(Inner)      as &J,
    2 => &Wrap3(Inner)      as &K,
    _ => loop {},
}

// LUB is `K` on nightly
match 0 {
    0 => &Wrap3(Inner)      as &I,
    1 => &Wrap3(Inner)      as &K,
    2 => &Wrap3(Inner)      as &J,
    _ => loop {},
}

r? ghost

jackh726 · 2025-12-26T21:40:10Z

@bors try @rust-timer queue

[CRATER] Require equality for symmetric LUB coercion

rust-bors · 2025-12-26T23:52:18Z

☀️ Try build successful (CI)
Build commit: bac5816 (bac5816c5f3d02cebd0599070af62d1782530294, parent: 82dd3cb008233bfe50ba6b8d6618e6bbd6054eb1)

rust-timer · 2025-12-27T00:33:03Z

Finished benchmarking commit (bac5816): comparison URL.

Overall result: ❌ regressions - 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)	0.4%	[0.1%, 0.9%]	22
Regressions ❌ (secondary)	3.8%	[0.1%, 9.6%]	31
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.4%	[0.1%, 0.9%]	22

Max RSS (memory usage)

Results (primary 0.8%, secondary 1.5%)

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

	mean	range	count
Regressions ❌ (primary)	3.7%	[1.3%, 9.1%]	4
Regressions ❌ (secondary)	2.2%	[1.1%, 2.8%]	3
Improvements ✅ (primary)	-5.1%	[-5.4%, -4.8%]	2
Improvements ✅ (secondary)	-0.7%	[-0.7%, -0.7%]	1
All ❌✅ (primary)	0.8%	[-5.4%, 9.1%]	6

Cycles

Results (primary -2.8%, secondary 5.9%)

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

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	5.9%	[4.4%, 7.7%]	8
Improvements ✅ (primary)	-2.8%	[-3.8%, -1.4%]	12
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-2.8%	[-3.8%, -1.4%]	12

Binary size

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

Bootstrap: 492.292s -> 484.36s (-1.61%)
Artifact size: 392.38 MiB -> 392.44 MiB (0.02%)

jackh726 · 2025-12-27T00:44:20Z

@craterbot check

craterbot · 2025-12-27T00:44:47Z

👌 Experiment pr-150408 created and queued.
🤖 Automatically detected try build bac5816
🔍 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 · 2026-01-02T21:52:38Z

🚧 Experiment pr-150408 is now running

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

craterbot · 2026-01-04T13:39:18Z

🎉 Experiment pr-150408 is completed!
📊 519 regressed and 4 fixed (768548 total)
📊 2039 spurious results on the retry-regressed-list.txt, consider a retry¹ if this is a significant amount.
📰 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

re-run the experiment with crates=https://crater-reports.s3.amazonaws.com/pr-150408/retry-regressed-list.txt ↩

jackh726 · 2026-01-10T21:53:49Z

@bors try

[CRATER] Require equality for symmetric LUB coercion

rust-bors · 2026-01-11T00:16:59Z

☀️ Try build successful (CI)
Build commit: 9bb5641 (9bb5641bfa3e7e0c9ede079ad0a1d43b1b7422bc, parent: f57eac1bf98cb5d578e3364b64365ec398c137df)

jackh726 · 2026-01-11T17:33:47Z

@craterbot run name=require-direct mode=check-only start=master#f57eac1bf98cb5d578e3364b64365ec398c137df end=try#9bb5641bfa3e7e0c9ede079ad0a1d43b1b7422bc crates=https://crater-reports.s3.amazonaws.com/pr-150408/retry-regressed-list.txt

craterbot · 2026-01-11T17:33:56Z

👌 Experiment require-direct created and queued.
🔍 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 · 2026-01-11T17:33:58Z

🚧 Experiment require-direct is now running

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

craterbot · 2026-01-11T21:05:33Z

🎉 Experiment require-direct is completed!
📊 0 regressed and 0 fixed (2455 total)
📊 159 spurious results on the retry-regressed-list.txt, consider a retry¹ if this is a significant amount.
📰 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

re-run the experiment with crates=https://crater-reports.s3.amazonaws.com/require-direct/retry-regressed-list.txt ↩

jackh726 · 2026-01-11T21:19:57Z

@rust-timer build 9bb5641

rust-timer · 2026-01-11T22:01:03Z

Finished benchmarking commit (9bb5641): 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)	0.3%	[0.3%, 0.4%]	3
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.2%	[-0.2%, -0.2%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.2%	[-0.2%, 0.4%]	4

Max RSS (memory usage)

Results (primary 0.8%, secondary -0.1%)

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

	mean	range	count
Regressions ❌ (primary)	2.4%	[2.4%, 2.4%]	1
Regressions ❌ (secondary)	2.1%	[1.8%, 2.5%]	4
Improvements ✅ (primary)	-0.9%	[-0.9%, -0.9%]	1
Improvements ✅ (secondary)	-1.8%	[-2.3%, -0.6%]	5
All ❌✅ (primary)	0.8%	[-0.9%, 2.4%]	2

Cycles

Results (secondary -2.4%)

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

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.4%	[-2.4%, -2.4%]	1
All ❌✅ (primary)	-	-	0

Binary size

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

Bootstrap: 473.812s -> 473.223s (-0.12%)
Artifact size: 391.34 MiB -> 391.33 MiB (-0.00%)

jackh726 · 2026-01-11T22:02:28Z

@bors try

[CRATER] Require equality for symmetric LUB coercion

rust-bors · 2026-01-12T00:18:58Z

☀️ Try build successful (CI)
Build commit: 94382f3 (94382f34384023f3d2062a34ccf0bb6b4d44a75a, parent: 7c41ee66db9d08e3989858acaefa1c72a6a88518)

jackh726 · 2026-01-12T03:38:50Z

@craterbot run name=mutual-coercion mode=check-only start=master#7c41ee66db9d08e3989858acaefa1c72a6a88518 end=try#94382f34384023f3d2062a34ccf0bb6b4d44a75a crates=https://crater-reports.s3.amazonaws.com/pr-150408/retry-regressed-list.txt

craterbot · 2026-01-12T03:38:54Z

👌 Experiment mutual-coercion created and queued.
🔍 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 · 2026-01-12T03:39:38Z

🚧 Experiment mutual-coercion is now running

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

jackh726 · 2026-01-12T03:39:56Z

@rust-timer build 94382f3

rust-timer · 2026-01-12T04:21:03Z

Finished benchmarking commit (94382f3): comparison URL.

Overall result: ❌ regressions - 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)	0.3%	[0.2%, 0.5%]	14
Regressions ❌ (secondary)	4.0%	[0.2%, 9.7%]	28
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.3%	[0.2%, 0.5%]	14

Max RSS (memory usage)

Results (primary 2.7%)

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

	mean	range	count
Regressions ❌ (primary)	2.7%	[2.3%, 3.0%]	2
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	2.7%	[2.3%, 3.0%]	2

Cycles

Results (primary -2.4%, secondary 4.7%)

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

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	4.7%	[3.9%, 5.4%]	12
Improvements ✅ (primary)	-2.4%	[-2.5%, -2.3%]	2
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-2.4%	[-2.5%, -2.3%]	2

Binary size

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

Bootstrap: 473.762s -> 472.906s (-0.18%)
Artifact size: 391.43 MiB -> 391.44 MiB (0.00%)

craterbot · 2026-01-12T08:16:51Z

🎉 Experiment mutual-coercion is completed!
📊 464 regressed and 0 fixed (2455 total)
📊 153 spurious results on the retry-regressed-list.txt, consider a retry¹ if this is a significant amount.
📰 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

re-run the experiment with crates=https://crater-reports.s3.amazonaws.com/mutual-coercion/retry-regressed-list.txt ↩

rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Dec 26, 2025