rustc_expand: improve diagnostics for non-repeatable metavars by Unique-Usman · Pull Request #152679 · rust-lang/rust

Unique-Usman · 2026-02-15T20:35:24Z

rustbot · 2026-02-15T20:35:29Z

rustbot has assigned @BoxyUwU.
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Unique-Usman · 2026-02-15T20:37:09Z

r? @estebank

Unique-Usman · 2026-02-15T20:37:30Z

This is rebased on top of ->791ee34

rustbot · 2026-02-20T14:59:55Z

This PR was rebased onto a different main 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.

compiler/rustc_expand/src/mbe/diagnostics.rs

compiler/rustc_expand/src/mbe/macro_rules.rs

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

Unique-Usman · 2026-02-23T21:02:34Z

@estebank - this is ready to land. Thank you for the review.

estebank · 2026-02-24T16:06:44Z

@bors r+

rust-bors · 2026-02-24T16:06:47Z

📌 Commit 93b9973 has been approved by estebank

It is now in the queue for this repository.

Unique-Usman · 2026-02-24T16:20:07Z

this #47452 should be closed now ?

estebank · 2026-02-24T17:04:35Z

Updated the description so that when the PR merges the ticket gets autoclosed.

…le, r=estebank rustc_expand: improve diagnostics for non-repeatable metavars Fix rust-lang#47452.

Rollup of 8 pull requests Successful merges: - #149169 (ptr::replace: make calls on ZST null ptr not UB) - #150562 (Fix doc link used in suggestion for pinning self) - #152679 (rustc_expand: improve diagnostics for non-repeatable metavars) - #153017 (Implement debuginfo for unsafe binder types) - #152868 (delete some very old trivial `Box` tests) - #152922 (rustc_public: Make fields that shouldn't be exposed visible only in `rustc_public`) - #153029 (Rename `rustc::pass_by_value` lint as `rustc::disallowed_pass_by_ref`.) - #153051 (Migration of `LintDiagnostic` - part 3)

Rollup of 12 pull requests Successful merges: - #149169 (ptr::replace: make calls on ZST null ptr not UB) - #150562 (Fix doc link used in suggestion for pinning self) - #152418 (`BTreeMap::merge` optimized) - #152679 (rustc_expand: improve diagnostics for non-repeatable metavars) - #152952 (mGCA: improve ogca diagnostic message ) - #152977 (Fix relative path handling for --extern-html-root-url) - #153017 (Implement debuginfo for unsafe binder types) - #152868 (delete some very old trivial `Box` tests) - #152922 (rustc_public: Make fields that shouldn't be exposed visible only in `rustc_public`) - #153032 (Fix attribute parser and kind names.) - #153051 (Migration of `LintDiagnostic` - part 3) - #153060 (Give a better error when updating a submodule fails)

Rollup merge of #152679 - Unique-Usman:ua/decmacrounrepeatable, r=estebank rustc_expand: improve diagnostics for non-repeatable metavars Fix #47452.

Kobzol · 2026-02-25T11:23:51Z

@rust-timer build 2f7d51a

For #153074.

rust-timer · 2026-02-25T11:23:54Z

Missing artifact for sha 2f7d51a313739380dbe5fa7a71454821a3a8df04 (https://ci-artifacts.rust-lang.org/rustc-builds/2f7d51a313739380dbe5fa7a71454821a3a8df04/rustc-nightly-x86_64-unknown-linux-gnu.tar.xz); not built yet, try again later.

JonathanBrouwer · 2026-02-25T12:21:43Z

@rust-timer build 2f7d51a

rust-timer · 2026-02-25T16:07:27Z

Finished benchmarking commit (2f7d51a): 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)	2.0%	[0.2%, 4.9%]	43
Regressions ❌ (secondary)	0.9%	[0.2%, 3.3%]	25
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	2.0%	[0.2%, 4.9%]	43

Max RSS (memory usage)

Results (primary 1.7%, secondary -4.0%)

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

	mean	range	count
Regressions ❌ (primary)	1.7%	[1.7%, 1.7%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-4.0%	[-4.0%, -4.0%]	1
All ❌✅ (primary)	1.7%	[1.7%, 1.7%]	1

Cycles

Results (primary 2.2%, secondary -1.6%)

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

	mean	range	count
Regressions ❌ (primary)	2.2%	[2.0%, 2.5%]	5
Regressions ❌ (secondary)	2.0%	[2.0%, 2.0%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-3.4%	[-3.9%, -2.8%]	2
All ❌✅ (primary)	2.2%	[2.0%, 2.5%]	5

Binary size

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

Bootstrap: 482.035s -> 479.929s (-0.44%)
Artifact size: 397.81 MiB -> 397.73 MiB (-0.02%)

JonathanBrouwer · 2026-02-25T16:11:37Z

Oof, that's a significant regression :c
What is the best way forward? Revert?

Kobzol · 2026-02-25T16:14:15Z

Seems like there might be room for improvement here, e.g. merge the two Vecs together, do not always fill them, use an arena or something, or others. But given the scale of the regression, I'd suggest reverting it first.

JonathanBrouwer · 2026-02-25T16:21:13Z

Created a revert PR here: #153095

estebank · 2026-02-25T19:55:57Z

Yes, lets revert and clean up.

estebank · 2026-02-25T19:58:39Z

compiler/rustc_expand/src/mbe/macro_rules.rs

+            let mut bindings = vec![];
+            for rule in rules {
+                let MacroRule::Func { lhs, .. } = rule else { continue };
+                for param in lhs {
+                    let MatcherLoc::MetaVarDecl { bind, .. } = param else { continue };
+                    bindings.push(*bind);
+                }
+            }
+
+            let mut matched_rule_bindings = vec![];
+            for param in lhs {
+                let MatcherLoc::MetaVarDecl { bind, .. } = param else { continue };
+                matched_rule_bindings.push(*bind);
+            }


Without closely looking at the lifetimes, it might be that we can pass lhs and rules to from_tts and move this logic to the error code path.

rustbot assigned BoxyUwU Feb 15, 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 Feb 15, 2026

rustbot assigned estebank and unassigned BoxyUwU Feb 15, 2026

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Unique-Usman force-pushed the ua/decmacrounrepeatable branch from 0fbe120 to 81f68bb Compare February 15, 2026 21:33

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Unique-Usman force-pushed the ua/decmacrounrepeatable branch from 81f68bb to 60060dd Compare February 20, 2026 14:59

estebank approved these changes Feb 23, 2026

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Unique-Usman force-pushed the ua/decmacrounrepeatable branch from 9704509 to d4e8858 Compare February 23, 2026 20:17

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rustc_expand: improve diagnostics for non-repeatable metavars

93b9973

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

Unique-Usman force-pushed the ua/decmacrounrepeatable branch from d4e8858 to 93b9973 Compare February 23, 2026 21:01

Unique-Usman requested a review from estebank February 23, 2026 21:01

rust-bors bot 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 Feb 24, 2026

GuillaumeGomez added a commit to GuillaumeGomez/rust that referenced this pull request Feb 24, 2026

Rollup merge of rust-lang#152679 - Unique-Usman:ua/decmacrounrepeatab…

0e14061

…le, r=estebank rustc_expand: improve diagnostics for non-repeatable metavars Fix rust-lang#47452.

GuillaumeGomez mentioned this pull request Feb 24, 2026

Rollup of 8 pull requests #153059

Closed

jhpratt mentioned this pull request Feb 25, 2026

Rollup of 12 pull requests #153074

Merged

rust-bors bot merged commit 35391c8 into rust-lang:main Feb 25, 2026
11 checks passed

rustbot added this to the 1.95.0 milestone Feb 25, 2026

rust-timer added a commit that referenced this pull request Feb 25, 2026

Unrolled build for #152679

2f7d51a

Rollup merge of #152679 - Unique-Usman:ua/decmacrounrepeatable, r=estebank rustc_expand: improve diagnostics for non-repeatable metavars Fix #47452.

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rustbot added the perf-regression Performance regression. label Feb 25, 2026

JonathanBrouwer mentioned this pull request Feb 25, 2026

Revert "rustc_expand: improve diagnostics for non-repeatable metavars" #153095

Open

estebank reviewed Feb 25, 2026

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rust-timer commented Feb 25, 2026

Overall result: ❌ regressions - please read the text below

Instruction count

Max RSS (memory usage)

Cycles

Binary size

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JonathanBrouwer commented Feb 25, 2026

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Unique-Usman commented Feb 15, 2026 •

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