rustc_expand: improve diagnostics for non-repeatable metavars by Unique-Usman · Pull Request #154014 · rust-lang/rust

Unique-Usman · 2026-03-17T21:03:07Z

There was an initally opened pr which solve this issue here #152679. It got merged but, there was a perf regression. And this new pr is opened to address the problem. The first did the computation of binding and matched_rule and then passed them as owned value down to diagnostics::emit_frag_parse_err( but, now this pr address the issue by passing lhs and rules as borrowed value to from_tts and the move the logic to diagnostics::emit_frag_parse_err(.

Fix #47452.

rustbot · 2026-03-17T21:03:13Z

r? @adwinwhite

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Unique-Usman · 2026-03-17T21:03:42Z

r? @estebank

estebank · 2026-03-23T17:23:10Z

@bors try @rust-timer queue

rustc_expand: improve diagnostics for non-repeatable metavars

rust-bors · 2026-03-23T19:32:22Z

☀️ Try build successful (CI)
Build commit: c7819c5 (c7819c57c7c6744e29582575ea34a29d6e8a3905, parent: 13e2abaac846b2680ae93e1b3bd9fe7fe1b9a7fe)

rust-timer · 2026-03-23T20:26:43Z

Finished benchmarking commit (c7819c5): 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)	0.2%	[0.2%, 0.2%]	6
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.2%	[0.2%, 0.2%]	6

Max RSS (memory usage)

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

Cycles

Results (secondary -0.5%)

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)	1.9%	[1.9%, 1.9%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.9%	[-2.9%, -2.9%]	1
All ❌✅ (primary)	-	-	0

Binary size

Results (primary 0.1%, 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)	0.1%	[0.0%, 0.1%]	55
Regressions ❌ (secondary)	0.1%	[0.0%, 0.2%]	24
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.1%	[0.0%, 0.1%]	55

Bootstrap: 482.731s -> 482.467s (-0.05%)
Artifact size: 396.84 MiB -> 396.93 MiB (0.02%)

estebank · 2026-03-24T02:20:45Z

The regressions here are all in html5ever. I think this should be fine.

@Unique-Usman could you provide a description, a link to the previous PR and squash the commits?

Unique-Usman · 2026-03-24T02:25:15Z

@estebank, I will do that. Thanks.

Co-authored-by: Esteban Küber <esteban@kuber.com.ar> Signed-off-by: Usman Akinyemi <usmanakinyemi202@gmail.com>

estebank · 2026-03-24T18:04:37Z

@bors try @rust-timer queue

getting some confirmation on the html5ever incr regression

rustc_expand: improve diagnostics for non-repeatable metavars

rust-bors · 2026-03-24T20:14:48Z

☀️ Try build successful (CI)
Build commit: 9837802 (983780242f7d36e76c1d0da9177445d96d292976, parent: 0312931d8c0ba1a28268a12c06202b68cbc65f76)

rust-timer · 2026-03-24T20:54:43Z

Finished benchmarking commit (9837802): 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%	[0.3%, 0.3%]	6
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.3%	[0.3%, 0.3%]	6

Max RSS (memory usage)

Results (secondary -2.5%)

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)	-2.5%	[-2.5%, -2.5%]	1
All ❌✅ (primary)	-	-	0

Cycles

Results (secondary -0.5%)

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)	3.0%	[2.9%, 3.1%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.9%	[-4.1%, -2.1%]	3
All ❌✅ (primary)	-	-	0

Binary size

Results (primary 0.1%, 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)	0.1%	[0.0%, 0.1%]	54
Regressions ❌ (secondary)	0.1%	[0.0%, 0.1%]	22
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.1%	[0.0%, 0.1%]	54

Bootstrap: 484.31s -> 483.312s (-0.21%)
Artifact size: 394.79 MiB -> 396.88 MiB (0.53%)

estebank · 2026-03-25T19:14:40Z

It consistently affects html5ever incr builds a little bit (we are doing more after all), but I think the output improvement is worth it.

@bors r+

rust-bors · 2026-03-25T19:14:44Z

📌 Commit ed4a1f8 has been approved by estebank

It is now in the queue for this repository.

rust-bors · 2026-03-26T02:20:52Z

☀️ Test successful - CI
Approved by: estebank
Duration: 3h 6m 27s
Pushing 1174f78 to main...

github-actions · 2026-03-26T02:23:52Z

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 80d0e4b (parent) -> 1174f78 (this PR)

Test differences

Show 8 test diffs

Stage 1

[ui] tests/ui/macros/typo-in-norepeat-expr-2.rs: [missing] -> pass (J2)
[ui] tests/ui/macros/typo-in-norepeat-expr.rs: [missing] -> pass (J2)

Stage 2

[ui] tests/ui/macros/typo-in-norepeat-expr-2.rs: [missing] -> pass (J0)
[ui] tests/ui/macros/typo-in-norepeat-expr.rs: [missing] -> pass (J0)
[run-make] tests/run-make/compressed-debuginfo-zstd: ignore (ignored if LLVM wasn't build with zstd for ELF section compression or LLVM is not the default codegen backend) -> pass (J1)

Additionally, 3 doctest diffs were found. These are ignored, as they are noisy.

Job group index

Test dashboard

Run

cargo run --manifest-path src/ci/citool/Cargo.toml -- \
    test-dashboard 1174f784096deb8e4ba93f7e4b5ccb7bb4ba2c55 --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

pr-check-1: 45m 27s -> 28m 4s (-38.2%)
x86_64-gnu-tools: 1h 22m -> 52m 53s (-36.2%)
pr-check-2: 56m 16s -> 38m 39s (-31.3%)
x86_64-rust-for-linux: 1h 8m -> 47m 12s (-30.8%)
x86_64-gnu-gcc: 1h 26m -> 1h 2m (-27.6%)
dist-aarch64-apple: 2h 13m -> 1h 37m (-27.0%)
dist-arm-linux-musl: 2h 11m -> 1h 37m (-25.7%)
dist-android: 36m 6s -> 27m 3s (-25.1%)
armhf-gnu: 1h 53m -> 1h 26m (-24.3%)
x86_64-gnu-miri: 1h 52m -> 1h 26m (-23.3%)

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 · 2026-03-26T03:01:21Z

Finished benchmarking commit (1174f78): 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%, 0.3%]	7
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.1%	[-0.1%, -0.1%]	1
Improvements ✅ (secondary)	-0.2%	[-0.2%, -0.2%]	1
All ❌✅ (primary)	0.2%	[-0.1%, 0.3%]	8

Max RSS (memory usage)

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

Cycles

Results (secondary -0.8%)

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)	2.2%	[2.2%, 2.2%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-3.9%	[-3.9%, -3.9%]	1
All ❌✅ (primary)	-	-	0

Binary size

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

Bootstrap: 481.885s -> 483.566s (0.35%)
Artifact size: 395.19 MiB -> 395.05 MiB (-0.04%)

rustbot assigned adwinwhite Mar 17, 2026

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 Mar 17, 2026

rustbot assigned estebank and unassigned adwinwhite Mar 17, 2026

Unique-Usman marked this pull request as draft March 17, 2026 21:04

rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Mar 17, 2026