Remove `Ident::empty` #140252

nnethercote · 2025-04-24T12:37:42Z

All uses have been removed. And it's nonsensical: an identifier by definition has at least one char.

r? @oli-obk

nnethercote · 2025-04-24T12:41:05Z

Helps with #137978.

rustbot · 2025-04-25T05:26:08Z

fmease is on vacation.

Please choose another assignee.

rustbot · 2025-04-25T05:26:10Z

Some changes occurred in compiler/rustc_attr_parsing

cc @jdonszelmann

nnethercote · 2025-04-25T05:27:33Z

Oh, the first commit here is from #140095 and doesn't need to be reviewed; this PR shouldn't be merged until that one has been.

compiler/rustc_resolve/src/lib.rs

oli-obk · 2025-04-28T09:46:38Z

r=me when the other PR landed

@bors reviewed

bors · 2025-04-28T21:32:20Z

☔ The latest upstream changes (presumably #140388) made this pull request unmergeable. Please resolve the merge conflicts.

bors · 2025-05-09T01:41:02Z

☔ The latest upstream changes (presumably #140818) made this pull request unmergeable. Please resolve the merge conflicts.

All uses have been removed. And it's nonsensical: an identifier by definition has at least one char. The commits adds an is-non-empty assertion to `Ident::new` to enforce this, and converts some `Ident` constructions to use `Ident::new`. Adding the assertion requires making `Ident::new` and `Ident::with_dummy_span` non-const, which is no great loss. The commit amends a couple of places that do path splitting to ensure no empty identifiers are created.

nnethercote · 2025-05-09T04:10:18Z

#140095 has been merged and I have updated.

@bors r=oli-obk

bors · 2025-05-09T04:10:20Z

📌 Commit 0984db5 has been approved by oli-obk

It is now in the queue for this repository.

bors · 2025-05-09T05:16:47Z

⌛ Testing commit 0984db5 with merge a7b1b24...

bors · 2025-05-09T08:30:12Z

☀️ Test successful - checks-actions
Approved by: oli-obk
Pushing a7b1b24 to master...

github-actions · 2025-05-09T08:33:32Z

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 c8b7f32 (parent) -> a7b1b24 (this PR)

Test differences

No test diffs found

Test dashboard

Run

cargo run --manifest-path src/ci/citool/Cargo.toml -- \
    test-dashboard a7b1b24587dcbebf12455c41ed828d9b486487be --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-apple-various: 8598.3s -> 6205.5s (-27.8%)
x86_64-apple-2: 7352.0s -> 5902.6s (-19.7%)
dist-x86_64-apple: 9239.2s -> 7714.9s (-16.5%)
dist-arm-linux: 4512.7s -> 5004.9s (10.9%)
dist-loongarch64-linux: 6603.6s -> 6049.9s (-8.4%)
dist-x86_64-mingw: 7519.9s -> 7920.4s (5.3%)
dist-x86_64-netbsd: 5169.5s -> 4948.5s (-4.3%)
dist-i686-msvc: 6811.7s -> 7091.8s (4.1%)
dist-i686-mingw: 7664.6s -> 7974.8s (4.0%)
dist-aarch64-apple: 5540.7s -> 5319.2s (-4.0%)

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 · 2025-05-09T10:05:04Z

Finished benchmarking commit (a7b1b24): comparison URL.

Overall result: ❌ regressions - 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

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)	0.3%	[0.1%, 1.1%]	115
Regressions ❌ (secondary)	0.4%	[0.2%, 0.7%]	41
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.3%	[0.1%, 1.1%]	115

Max RSS (memory usage)

Results (primary 0.5%, secondary -2.6%)

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)	1.4%	[0.4%, 5.1%]	9
Regressions ❌ (secondary)	1.2%	[1.2%, 1.2%]	1
Improvements ✅ (primary)	-1.6%	[-3.0%, -0.4%]	4
Improvements ✅ (secondary)	-4.6%	[-5.2%, -4.0%]	2
All ❌✅ (primary)	0.5%	[-3.0%, 5.1%]	13

Cycles

Results (primary 0.5%, secondary 2.6%)

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)	0.6%	[0.4%, 0.9%]	13
Regressions ❌ (secondary)	2.6%	[2.4%, 2.7%]	2
Improvements ✅ (primary)	-0.5%	[-0.5%, -0.4%]	2
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.5%	[-0.5%, 0.9%]	15

Binary size

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

Bootstrap: 771.811s -> 772.392s (0.08%)
Artifact size: 365.31 MiB -> 365.74 MiB (0.12%)

nnethercote · 2025-05-09T11:19:54Z

Ugh, perf regressions were not expected. I'll take a look, though I might not get to it until after RustWeek.

This fixes a perf regression introduced in rust-lang#140252.

nnethercote · 2025-05-09T23:41:11Z

#140880 should fix the perf regressions.

…r=<try> Make the assertion in `Ident::new` debug-only. This fixes a perf regression introduced in rust-lang#140252. r? `@oli-obk`

…r=oli-obk Make the assertion in `Ident::new` debug-only. This fixes a perf regression introduced in rust-lang#140252. r? `@oli-obk`

nnethercote · 2025-05-10T22:53:21Z

#140880 has merged.

@rustbot label: +perf-regression-triaged

It was added in rust-lang#140052, but the subsequent changes in rust-lang#140252 means it is no longer necessary. (Indeed, `Ident`s cannot be empty any more.)

This fixes a perf regression introduced in rust-lang#140252. (cherry picked from commit 4cb9f03)

nnethercote force-pushed the rm-Ident-empty branch from ccb01ef to 3e46e7b Compare April 24, 2025 12:40

nnethercote force-pushed the rm-Ident-empty branch from 3e46e7b to 889e4c6 Compare April 25, 2025 05:25

nnethercote marked this pull request as ready for review April 25, 2025 05:26

rustbot assigned oli-obk Apr 25, 2025

oli-obk approved these changes Apr 28, 2025

View reviewed changes

compiler/rustc_resolve/src/lib.rs Outdated Show resolved Hide resolved

oli-obk 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 Apr 28, 2025

nnethercote force-pushed the rm-Ident-empty branch from 889e4c6 to e7efeff Compare April 28, 2025 20:20

nnethercote force-pushed the rm-Ident-empty branch from e7efeff to 40952d7 Compare April 28, 2025 22:35

nnethercote force-pushed the rm-Ident-empty branch from 40952d7 to 0984db5 Compare May 9, 2025 04:09

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-author Status: This is awaiting some action (such as code changes or more information) from the author. labels May 9, 2025

bors added the merged-by-bors This PR was explicitly merged by bors. label May 9, 2025

bors merged commit a7b1b24 into rust-lang:master May 9, 2025
7 checks passed

rustbot added this to the 1.88.0 milestone May 9, 2025

rustbot added the perf-regression Performance regression. label May 9, 2025

nnethercote deleted the rm-Ident-empty branch May 9, 2025 23:17

nnethercote added a commit to nnethercote/rust that referenced this pull request May 9, 2025

Make the assertion in Ident::new debug-only.

4cb9f03

This fixes a perf regression introduced in rust-lang#140252.

nnethercote mentioned this pull request May 9, 2025

Make the assertion in Ident::new debug-only. #140880

Merged

matthiaskrgr mentioned this pull request May 10, 2025

ICE: symbol: assertion left != right failed #140884

Closed

rustbot added the perf-regression-triaged The performance regression has been triaged. label May 10, 2025

nnethercote mentioned this pull request May 22, 2025

Remove unnecessary is_empty checks #141377

Merged

cuviper pushed a commit to cuviper/rust that referenced this pull request Jun 20, 2025

Make the assertion in Ident::new debug-only.

281a202

This fixes a perf regression introduced in rust-lang#140252. (cherry picked from commit 4cb9f03)

Remove Ident::empty #140252

Remove Ident::empty #140252

Uh oh!

Conversation

nnethercote commented Apr 24, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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nnethercote commented Apr 24, 2025

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rustbot commented Apr 25, 2025

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rustbot commented Apr 25, 2025

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nnethercote commented Apr 25, 2025

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oli-obk commented Apr 28, 2025

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bors commented Apr 28, 2025

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bors commented May 9, 2025

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nnethercote commented May 9, 2025

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bors commented May 9, 2025

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bors commented May 9, 2025

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bors commented May 9, 2025

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github-actions bot commented May 9, 2025

Test differences

Job duration changes

Uh oh!

rust-timer commented May 9, 2025

Overall result: ❌ regressions - please read the text below

Instruction count

Max RSS (memory usage)

Cycles

Binary size

Uh oh!

nnethercote commented May 9, 2025

Uh oh!

nnethercote commented May 9, 2025

Uh oh!

nnethercote commented May 10, 2025

Uh oh!

Uh oh!

Remove `Ident::empty` #140252

Remove `Ident::empty` #140252

nnethercote commented Apr 24, 2025 •

edited

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