Improve source code for `highlight.rs` by GuillaumeGomez · Pull Request #146992 · rust-lang/rust

GuillaumeGomez · 2025-09-24T16:34:12Z

I was very bothered by the complexity of this file, in particular the handling of pending_elems which was very tricky to follow.

So instead, here comes a more sane approach: the content is store in a stack-like type which handles "levels" of HTML (ie, a macro expansion can contain other HTML tags which can themselves contain other, etc). Making it much simpler to keep track of what's going on.

r? @lolbinarycat

GuillaumeGomez · 2025-09-24T16:34:52Z

Also need to check the impact on performance (likely slower).

@bors try @rust-timer queue

Improve source code for `highlight.rs`

rust-bors · 2025-09-24T18:48:51Z

☀️ Try build successful (CI)
Build commit: 6020c97 (6020c97e3046a35e53fd9885eda164c570010a6c, parent: 15283f6fe95e5b604273d13a428bab5fc0788f5a)

src/librustdoc/html/highlight.rs

yotamofek · 2025-09-24T19:44:11Z

Code reads much better IMHO!

rust-timer · 2025-09-24T19:59:22Z

Finished benchmarking commit (6020c97): 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)	2.2%	[0.7%, 6.6%]	19
Regressions ❌ (secondary)	3.2%	[0.1%, 13.3%]	17
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	2.2%	[0.7%, 6.6%]	19

Max RSS (memory usage)

Results (primary 0.4%, secondary 12.0%)

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

	mean	range	count
Regressions ❌ (primary)	6.2%	[6.2%, 6.2%]	1
Regressions ❌ (secondary)	12.0%	[2.6%, 31.9%]	6
Improvements ✅ (primary)	-2.5%	[-2.8%, -2.2%]	2
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.4%	[-2.8%, 6.2%]	3

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)	4.3%	[3.2%, 6.5%]	3
Regressions ❌ (secondary)	8.3%	[3.6%, 12.8%]	6
Improvements ✅ (primary)	-1.6%	[-1.6%, -1.6%]	1
Improvements ✅ (secondary)	-1.5%	[-1.5%, -1.4%]	2
All ❌✅ (primary)	2.8%	[-1.6%, 6.5%]	4

Binary size

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

Bootstrap: 471.213s -> 470.794s (-0.09%)
Artifact size: 387.83 MiB -> 387.93 MiB (0.03%)

GuillaumeGomez · 2025-09-24T22:39:50Z

Code reads much better IMHO!

Agreed (unsurprisingly 😆), but sadly I think this solution is unlikely to get much better performance-wise so unlikely it'll be merged.

However I now have a much cleaner code, so I think I'll go back to the original "streaming content" but with a much cleaner approach.

lolbinarycat · 2025-09-25T16:31:24Z

If I had to guess the reason for the perf regression, I would say it probably has to do with all the extra intermediate string allocations. I feel like if we had a way to delay formatting (maybe using an enum, or with dyn Display, or just make it so the final writer is given up front), this would have a lot less overhead.

GuillaumeGomez · 2025-09-25T16:46:33Z

Possibly. Want to give a try pushing it even further before I try to turn this back into a streaming algorithm? Same question for you @yotamofek. 😉

Start from my branch and open PRs with your commits so we can run perf check on them.

yotamofek · 2025-09-25T17:07:32Z

I'll give it a go, but my gut says the extra string allocations aren't causing the lion's share of the regressions. Worth a shot though

bors · 2025-09-26T01:17:09Z

☔ The latest upstream changes (presumably #147037) made this pull request unmergeable. Please resolve the merge conflicts.

bors · 2025-10-06T16:52:19Z

☔ The latest upstream changes (presumably #147397) made this pull request unmergeable. Please resolve the merge conflicts.

GuillaumeGomez · 2025-10-07T13:05:38Z

So I realized that there are some bugs in the existing code which are fixed by this PR:

In the example above, only self should be underlined, not the whitespace. Anyway, looking a bit more into this performance issue.

rustbot · 2025-10-23T16:10:19Z

This PR was rebased onto a different master commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

GuillaumeGomez · 2025-10-23T16:10:25Z

Applied suggestions and rebased.

… `closing_tags` Improve documentation Improve code

GuillaumeGomez · 2025-10-23T19:48:01Z

Arf, english typo, my nemesis. Convenient check. Anyway, the typo checker should be happy now. :)

yotamofek

Approving, but see this comment: #146992 (comment)
Nothing I can think of other than that.

Really cool change!

View changes since this review

GuillaumeGomez · 2025-10-26T14:36:22Z

Thanks for the review. Considering it's fixing bugs, gonna improve the code in a follow-up.

@bors r=yotamofek,lolbinarycat rollup

bors · 2025-10-26T14:36:25Z

📌 Commit ab1dcee has been approved by yotamofek,lolbinarycat

It is now in the queue for this repository.

bors · 2025-10-26T17:31:25Z

⌛ Testing commit ab1dcee with merge f977dfc...

bors · 2025-10-26T20:35:55Z

☀️ Test successful - checks-actions
Approved by: yotamofek,lolbinarycat
Pushing f977dfc to master...

github-actions · 2025-10-26T20:39:20Z

What is this?

This is an experimental post-merge analysis report that shows differences in test outcomes between the merged PR and its parent PR.

Comparing 2888098 (parent) -> f977dfc (this PR)

Test differences

Show 5 test diffs

5 doctest diffs were found. These are ignored, as they are noisy.

Test dashboard

Run

cargo run --manifest-path src/ci/citool/Cargo.toml -- \
    test-dashboard f977dfc388ea39c9886b7f8c49abce26e6918df6 --output-dir test-dashboard

And then open test-dashboard/index.html in your browser to see an overview of all executed tests.

Job duration changes

dist-aarch64-msvc: 5386.0s -> 6290.8s (16.8%)
dist-various-1: 3687.9s -> 4219.5s (14.4%)
pr-check-1: 1294.5s -> 1463.9s (13.1%)
aarch64-apple: 7673.6s -> 6895.9s (-10.1%)
dist-apple-various: 3604.6s -> 3241.1s (-10.1%)
x86_64-gnu-gcc: 3070.7s -> 2776.9s (-9.6%)
arm-android: 5419.7s -> 5917.9s (9.2%)
x86_64-gnu-stable: 7065.9s -> 6521.7s (-7.7%)
x86_64-mingw-2: 7979.9s -> 7381.3s (-7.5%)
dist-x86_64-musl: 8340.5s -> 7762.2s (-6.9%)

How to interpret the job duration changes?

Job durations can vary a lot, based on the actual runner instance
that executed the job, system noise, invalidated caches, etc. The table above is provided
mostly for t-infra members, for simpler debugging of potential CI slow-downs.

rust-timer · 2025-10-26T21:46:51Z

Finished benchmarking commit (f977dfc): comparison URL.

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

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)	0.2%	[0.1%, 0.2%]	6
Regressions ❌ (secondary)	0.2%	[0.1%, 0.3%]	3
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.1%	[-0.1%, -0.1%]	1
All ❌✅ (primary)	0.2%	[0.1%, 0.2%]	6

Max RSS (memory usage)

Results (primary -1.2%, 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)	-	-	0
Regressions ❌ (secondary)	2.4%	[2.4%, 2.4%]	1
Improvements ✅ (primary)	-1.2%	[-1.2%, -1.2%]	1
Improvements ✅ (secondary)	-2.8%	[-2.8%, -2.8%]	1
All ❌✅ (primary)	-1.2%	[-1.2%, -1.2%]	1

Cycles

Results (secondary -2.7%)

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)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.7%	[-2.7%, -2.7%]	1
All ❌✅ (primary)	-	-	0

Binary size

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

Bootstrap: 476.488s -> 473.751s (-0.57%)
Artifact size: 390.47 MiB -> 390.43 MiB (-0.01%)

panstromek · 2025-10-27T16:51:51Z

perf triage:

Small regressions were expected base from the pre-merge run and following comment: #146992 (comment). Overall the impact is not big and looks partially like noise, since the results got better in next PR (which is unrelated).

@rustbot label: +perf-regression-triaged

…ht, r=yotamofek,lolbinarycat Simplify code to generate line numbers in highlight Follow-up of rust-lang#146992. cc `@yotamofek` r? `@lolbinarycat`

…ht, r=yotamofek,lolbinarycat Simplify code to generate line numbers in highlight Follow-up of rust-lang#146992. cc ``@yotamofek`` r? ``@lolbinarycat``

…ht, r=yotamofek,lolbinarycat Simplify code to generate line numbers in highlight Follow-up of rust-lang#146992. cc ```@yotamofek``` r? ```@lolbinarycat```

…ht, r=yotamofek,lolbinarycat Simplify code to generate line numbers in highlight Follow-up of rust-lang#146992. cc ````@yotamofek```` r? ````@lolbinarycat````

…ht, r=yotamofek,lolbinarycat Simplify code to generate line numbers in highlight Follow-up of rust-lang#146992. cc `````@yotamofek````` r? `````@lolbinarycat`````

Rollup merge of #148171 - GuillaumeGomez:line-number-highlight, r=yotamofek,lolbinarycat Simplify code to generate line numbers in highlight Follow-up of #146992. cc `````@yotamofek````` r? `````@lolbinarycat`````

rustbot assigned lolbinarycat Sep 24, 2025

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Auto merge of #146992 - GuillaumeGomez:improve-highlight, r=<try>

6020c97

Improve source code for `highlight.rs`

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rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Sep 24, 2025

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yotamofek reviewed Sep 24, 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 Sep 24, 2025

GuillaumeGomez force-pushed the improve-highlight branch from dfcb725 to 957ca47 Compare September 27, 2025 21:25

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yotamofek mentioned this pull request Sep 27, 2025

Small highlight.rs optimizations #147106

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GuillaumeGomez force-pushed the improve-highlight branch from 957ca47 to 2ae1bf4 Compare October 7, 2025 12:42

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Merge ClassInfo::open and ClassInfo::link_closing_tag fields into…

ab1dcee

… `closing_tags` Improve documentation Improve code

GuillaumeGomez force-pushed the improve-highlight branch from e8f2462 to ab1dcee Compare October 23, 2025 19:47

yotamofek approved these changes Oct 26, 2025

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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 Oct 26, 2025

bors added the merged-by-bors This PR was explicitly merged by bors. label Oct 26, 2025

bors merged commit f977dfc into rust-lang:master Oct 26, 2025
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rustbot added this to the 1.93.0 milestone Oct 26, 2025

GuillaumeGomez deleted the improve-highlight branch October 27, 2025 10:25

GuillaumeGomez mentioned this pull request Oct 27, 2025

Simplify code to generate line numbers in highlight #148171

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rustbot added the perf-regression-triaged The performance regression has been triaged. label Oct 27, 2025

dtolnay mentioned this pull request Oct 27, 2025

ICE: exit_elem called on empty class stack #148184

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fmease mentioned this pull request Oct 31, 2025

Fix invalid tag closing when leaving expansion "original code" #148213

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Overall result: ❌ regressions - please read the text below

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Test differences

Job duration changes

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

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