librustdoc: create a helper for separating elements of an iterator instead of implementing it multiple times

[yotamofek]

This implements something similar to Itertools::format, but on Fns returning iterators instead of directly on iterators, to allow implementing Display without the use of a Cell (to handle the possibility of fmt being called multiple times while receiving &self).

This is WIP, I just want to get a perf run first to see if the regression I saw in #135494 is fixed

This was originally part of #135494 , but originally caused a perf regression that was since fixed:

rust/src/librustdoc/html/format.rs

Line 507 in 7d5ae18

// NOTE: using `Joined::joined` here causes a noticeable perf regression

[rustbot]

r? @GuillaumeGomez

rustbot has assigned @GuillaumeGomez.
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[GuillaumeGomez]

Seems very promising, thanks! Please tell me when you want to start the perf run.

[yotamofek]

Thanks! I'll ping you once CI checks are done (or can it be queued before they're finished? if so - go ahead please)

[GuillaumeGomez]

Unfortunately it's not queue, it's done on a separate server. So waiting for your ping then!

[yotamofek]

@GuillaumeGomez ping 😁

[GuillaumeGomez]

Let's go!

@bors try @rust-timer queue

[bors]

⌛ Trying commit 66e29e0 with merge f5cefbb...

[bors]

☀️ Try build successful - checks-actions
Build commit: f5cefbb (f5cefbbc06874f3ca9f2ce11fa5610b2fd97780c)

[rust-timer]

Finished benchmarking commit (f5cefbb): comparison URL.

Overall result: ❌ regressions - please read the text below

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.

Next Steps: If you can justify the regressions found in this try perf run, please indicate this with @rustbot label: +perf-regression-triaged along with sufficient written justification. If you cannot justify the regressions please fix the regressions and do another perf run. If the next run shows neutral or positive results, the label will be automatically removed.

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

Instruction count

This is the most reliable metric that we have; it was used to determine the overall result at the top of this comment. However, even this metric can sometimes exhibit noise.

	mean	range	count
Regressions ❌ (primary)	0.8%	[0.2%, 1.7%]	6
Regressions ❌ (secondary)	0.2%	[0.2%, 0.2%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.8%	[0.2%, 1.7%]	6

Max RSS (memory usage)

Results (secondary -1.3%)

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)	-1.3%	[-1.5%, -1.1%]	2
All ❌✅ (primary)	-	-	0

Cycles

Results (secondary -2.3%)

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)	-2.3%	[-2.3%, -2.3%]	1
All ❌✅ (primary)	-	-	0

Binary size

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

Bootstrap: 775.532s -> 776.62s (0.14%)
Artifact size: 328.40 MiB -> 328.46 MiB (0.02%)

[yotamofek]

Still regresses 😓
Back to the drawing board...

[GuillaumeGomez]

Please ping me whenever you want to give it another try. 😉

[yotamofek]

Ping 🙏

[GuillaumeGomez]

@bors try @rust-timer queue

[bors]

⌛ Trying commit 63abcb0 with merge e38cd65...

[bors]

☀️ Try build successful - checks-actions
Build commit: e38cd65 (e38cd65d26f9fb9c2e492cc9752f0b6fccffff0f)

[rust-timer]

Finished benchmarking commit (e38cd65): comparison URL.

Overall result: ❌ regressions - please read the text below

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.

Next Steps: If you can justify the regressions found in this try perf run, please indicate this with @rustbot label: +perf-regression-triaged along with sufficient written justification. If you cannot justify the regressions please fix the regressions and do another perf run. If the next run shows neutral or positive results, the label will be automatically removed.

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

Instruction count

This is the most reliable metric that we have; it was used to determine the overall result at the top of this comment. However, even this metric can sometimes exhibit noise.

	mean	range	count
Regressions ❌ (primary)	0.8%	[0.2%, 1.6%]	5
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.8%	[0.2%, 1.6%]	5

Max RSS (memory usage)

Results (primary 2.8%, secondary -1.3%)

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)	7.6%	[7.6%, 7.6%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-2.0%	[-2.0%, -2.0%]	1
Improvements ✅ (secondary)	-1.3%	[-1.3%, -1.3%]	1
All ❌✅ (primary)	2.8%	[-2.0%, 7.6%]	2

Cycles

Results (secondary 9.2%)

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)	9.2%	[9.2%, 9.2%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Binary size

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

Bootstrap: 776.896s -> 776.333s (-0.07%)
Artifact size: 328.47 MiB -> 328.48 MiB (0.00%)

[GuillaumeGomez]

Thanks!

@bors r+ rollup=iffy

[bors]

📌 Commit eb2635e has been approved by GuillaumeGomez

It is now in the queue for this repository.

[bors]

☔ The latest upstream changes (presumably #136507) made this pull request unmergeable. Please resolve the merge conflicts.

[yotamofek]

@rustbot review

[fmease]

Lol, oops. @bors r=GuillaumeGomez

[bors]

📌 Commit cb028dc has been approved by GuillaumeGomez

It is now in the queue for this repository.

[bors]

⌛ Testing commit cb028dc with merge 8df89d1...

[bors]

☀️ Test successful - checks-actions
Approved by: GuillaumeGomez
Pushing 8df89d1 to master...

[rust-timer]

Finished benchmarking commit (8df89d1): comparison URL.

Overall result: ✅ improvements - no action needed

@rustbot label: -perf-regression

Instruction count

This is the most reliable metric that we have; it was used to determine the overall result at the top of this comment. However, even this metric can sometimes exhibit noise.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.7%	[-0.8%, -0.6%]	2
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.7%	[-0.8%, -0.6%]	2

Max RSS (memory usage)

Results (primary 0.2%)

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)	3.5%	[3.5%, 3.5%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-3.2%	[-3.2%, -3.2%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.2%	[-3.2%, 3.5%]	2

Cycles

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

Binary size

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

Bootstrap: 777.31s -> 776.632s (-0.09%)
Artifact size: 328.75 MiB -> 328.78 MiB (0.01%)