[dianne]

Followup to #163958 that restores the functionality it removed it removed from #163200 and clarifies/fixes some of their comments. The following variant of #161621 is now accepted again:

trait HasAssoc {
    type Assoc;
}

trait Parent<T> {}

// We need to assume `<(RustaceansAreAwesome,) as HasAssoc>::Assoc == str`
// in order to prove `<(RustaceansAreAwesome,) as HasAssoc>::Assoc: ToOwned`

trait NeedProjectionNotInExpansion
where
    // The projection clause `<(Self,) as HasAssoc>::Assoc == str` isn't written
    // as part of a supertrait bound, so the expansion of `RustaceansAreAwesome:
    // NeedProjectionNotInExpansion` done by param-env normalization won't
    // include a version of it for `RustaceansAreAwesome`.
    (Self,): HasAssoc<Assoc = str>,
    Self: Parent<<<(Self,) as HasAssoc>::Assoc as ToOwned>::Owned>,
{
    fn f(&self);
}

It's unfortunate how tightly coupled this all is to particulars of param-env normalization. I'd love to remove these hacks eventually.

[dianne]

there's some room for optimization at the expense of clarity, but hopefully this isn't enough of a perf bottleneck that it's needed. let's see: @bors try @rust-timer queue

[rust-bors]

☀️ Try build successful (CI)
Build commit: 13ec746 (13ec7465f912c616165d45f16011ea5ae0af17d0)
Base parent: 39b126b (39b126b8e227197c688fed9f9962658bdd89a761)

[rust-timer]

Finished benchmarking commit (13ec746): comparison URL.

Overall result: no relevant changes - no action needed

Benchmarking means the PR may be perf-sensitive. Consider adding rollup=never if this change is not fit for rolling up.

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

Instruction count

This perf run didn't have relevant results for this metric.

Max RSS (memory usage)

This perf run didn't have relevant results for this metric.

Cycles

Results (primary -1.2%, secondary -1.3%)

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

	mean	range	count
Regressions ❌ (primary)	1.6%	[1.6%, 1.6%]	1
Regressions ❌ (secondary)	1.0%	[0.5%, 2.1%]	5
Improvements ✅ (primary)	-2.2%	[-2.3%, -2.1%]	3
Improvements ✅ (secondary)	-2.5%	[-6.6%, -0.4%]	9
All ❌✅ (primary)	-1.2%	[-2.3%, 1.6%]	4

Binary size

Results (primary -0.0%, secondary -0.0%)

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)	-0.0%	[-0.0%, -0.0%]	1
Improvements ✅ (secondary)	-0.0%	[-0.0%, -0.0%]	1
All ❌✅ (primary)	-0.0%	[-0.0%, -0.0%]	1

Bootstrap: 488.638s -> 489.098s (0.09%)
Artifact size: 409.06 MiB -> 409.11 MiB (0.01%)

[dianne]

r? oli-obk or reassign

[oli-obk]

@bors r+ rollup

View changes since this review

[rust-bors]

📌 Commit e712498 has been approved by oli-obk

It is now in the queue for this repository.

[rust-timer]

Note

This PR was benchmarked as part of triage of its containing rollup: triage URL.

Finished benchmarking commit (f98307f): comparison URL.

Overall result: ❌ regressions - please read:

Our benchmarks found a performance regression caused by this PR.
This might be an actual regression, but it can also be just noise.

Next Steps:

• If the regression was expected or you think it can be justified,
  please write a comment with sufficient written justification, and add
  @rustbot label: +perf-regression-triaged to it, to mark the regression as triaged.
• If you think that you know of a way to resolve the regression, try to create
  a new PR with a fix for the regression.
• If you do not understand the regression or you think that it is just noise,
  you can ask the @rust-lang/wg-compiler-performance working group for help (members of this group
  were already notified of this PR).

@rustbot label: +perf-regression
cc @rust-lang/wg-compiler-performance

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
Regressions ❌ (secondary)	0.3%	[0.0%, 0.5%]	11
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results (secondary -3.8%)

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)	-3.8%	[-5.9%, -1.8%]	2
All ❌✅ (primary)	-	-	0

Cycles

This perf run didn't have relevant results for this metric.

Binary size

This perf run didn't have relevant results for this metric.

Artifact size: 406.42 MiB -> 406.60 MiB (0.05%)