Make slice iterator constructors unstably const #137738

Daniel-Aaron-Bloom · 2025-02-27T16:41:11Z

See tracking issue for justification.

try-job: aarch64-apple
try-job: x86_64-gnu

rustbot · 2025-02-27T16:41:16Z

rustbot has assigned @thomcc.
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Daniel-Aaron-Bloom · 2025-02-27T16:43:17Z

@rustbot label -T-libs +T-libs-api

Daniel-Aaron-Bloom · 2025-02-27T16:43:48Z

r? libs-api

scottmcm · 2025-02-27T23:28:22Z

It's not obvious that these are desirable yet, since other could-trivially-be-const things like https://doc.rust-lang.org/nightly/std/iter/fn.once.html aren't. Probably worth a team decision on the broader question, then the reviews would be simple.

bors · 2025-03-16T06:09:37Z

☔ The latest upstream changes (presumably #138548) made this pull request unmergeable. Please resolve the merge conflicts.

dtolnay · 2025-03-28T02:31:13Z

This line from the tracking issue is spot on: "having unnecessary const limitations is preventing code reuse between const and non-const functions." I have personally experienced this much more often than I might have guessed. Writing some const fn gets stuck on some trivial standard library function not being const, look into the history of whether that function has been proposed to be const and why it isn't, and there is someone explaining why 'theoretically' nobody should ever want that function to be const because it would be useless. (Like for these iterator constructors, something like "because you can't call next on them in const anyway.") And yet…

So I buy the justification. This PR looks good to me as soon as you rebase to solve the merge conflict.

Daniel-Aaron-Bloom · 2025-04-01T05:09:15Z

@rustbot ready

tgross35 · 2025-04-01T06:27:38Z

Crosslinking the zulip discussion #t-libs-api/api-changes > const slice iterator constructors

…e_iter, r=dtolnay Make slice iterator constructors unstably const See [tracking issue](rust-lang#137737) for justification.

Rollup of 12 pull requests Successful merges: - rust-lang#110406 (rustdoc-json: Add test for #[automatically_derived] attribute) - rust-lang#137738 (Make slice iterator constructors unstably const) - rust-lang#138492 (remove `feature(inline_const_pat)`) - rust-lang#138928 (Fix UWP reparse point check) - rust-lang#138950 (replace extra_filename with strict version hash in metrics file names) - rust-lang#139002 (Add release notes for 1.86.0) - rust-lang#139022 (increment depth of nested obligations) - rust-lang#139060 (replace commit placeholder in vendor status with actual commit) - rust-lang#139102 (coverage: Avoid splitting spans during span extraction/refinement) - rust-lang#139129 (Add tests for slice bounds check optimization) - rust-lang#139188 (PassWrapper: adapt for llvm/llvm-project@94122d58fc77079a291a3d008914…) - rust-lang#139193 (Feed HIR for by-move coroutine body def, since the inliner tries to read its attrs) r? `@ghost` `@rustbot` modify labels: rollup

…iter, r=dtolnay Make slice iterator constructors unstably const See [tracking issue](rust-lang#137737) for justification.

bors · 2025-04-01T13:44:32Z

⌛ Testing commit beb8e9e with merge 88dae5c...

bors · 2025-04-01T14:19:39Z

💔 Test failed - checks-actions

tgross35 · 2025-04-02T17:33:52Z

@bors try

@Daniel-Aaron-Bloom could you squash? Also FYI those are MIR tests (the IR), nor Miri (the interpreter).

…iter, r=<try> Make slice iterator constructors unstably const See [tracking issue](rust-lang#137737) for justification. try-job: aarch64-apple try-job: x86_64-gnu

bors · 2025-04-02T17:35:06Z

⌛ Trying commit 7e4cbc4 with merge bddf132...

tgross35 · 2025-04-02T19:34:05Z

@bors r=dtolnay

bors · 2025-04-02T19:34:08Z

📌 Commit 20417a9 has been approved by dtolnay

It is now in the queue for this repository.

bors · 2025-04-03T08:57:49Z

⌛ Testing commit 20417a9 with merge e0883a2...

bors · 2025-04-03T12:04:22Z

☀️ Test successful - checks-actions
Approved by: dtolnay
Pushing e0883a2 to master...

github-actions · 2025-04-03T12:06:39Z

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 b6d74b5 (parent) -> e0883a2 (this PR)

Test differences

Show 485 test diffs

Stage 2

[run-make] tests/run-make/compressed-debuginfo-zstd: ignore (ignored if LLVM wasn't build with zstd for ELF section compression (we want LLVM/LLD to be built with zstd support)) -> pass (J0)

Additionally, 484 doctest diffs were found. These are ignored, as they are noisy.

Job group index

J0: x86_64-gnu-nopt

Job duration changes

dist-apple-various: 7774.8s -> 8824.2s (13.5%)
x86_64-apple-2: 5874.0s -> 6600.6s (12.4%)
x86_64-gnu-llvm-18-2: 5941.6s -> 6140.3s (3.3%)
x86_64-gnu-llvm-19-2: 6009.8s -> 6110.0s (1.7%)
dist-various-1: 4402.2s -> 4439.8s (0.9%)
i686-msvc-2: 7318.7s -> 7377.3s (0.8%)
dist-x86_64-msvc-alt: 7459.3s -> 7474.4s (0.2%)
x86_64-gnu-llvm-19-1: 5357.3s -> 5365.6s (0.2%)
x86_64-msvc-2: 6910.3s -> 6781.7s (-1.9%)
x86_64-gnu-llvm-19-3: 6922.3s -> 6792.5s (-1.9%)

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 · 2025-04-03T13:44:11Z

Finished benchmarking commit (e0883a2): comparison URL.

Overall result: ❌ regressions - 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)	0.3%	[0.3%, 0.3%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.3%	[0.3%, 0.3%]	1

Max RSS (memory usage)

Results (primary -2.0%, secondary -0.1%)

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)	2.0%	[2.0%, 2.0%]	1
Improvements ✅ (primary)	-2.0%	[-2.0%, -2.0%]	1
Improvements ✅ (secondary)	-2.1%	[-2.1%, -2.1%]	1
All ❌✅ (primary)	-2.0%	[-2.0%, -2.0%]	1

Cycles

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

Binary size

Results (primary -0.1%, secondary -0.1%)

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)	-0.1%	[-0.2%, -0.0%]	55
Improvements ✅ (secondary)	-0.1%	[-0.1%, -0.1%]	4
All ❌✅ (primary)	-0.1%	[-0.2%, -0.0%]	55

Bootstrap: 778.474s -> 777.235s (-0.16%)
Artifact size: 365.89 MiB -> 365.89 MiB (0.00%)

rustbot assigned thomcc Feb 27, 2025

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Feb 27, 2025

Daniel-Aaron-Bloom mentioned this pull request Feb 27, 2025

Tracking Issue for const_slice_make_iter #137737

Open

3 tasks

rustbot added T-libs-api Relevant to the library API team, which will review and decide on the PR/issue. and removed T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Feb 27, 2025

rustbot assigned m-ou-se and unassigned thomcc Feb 27, 2025

m-ou-se assigned scottmcm and unassigned m-ou-se Mar 18, 2025

dtolnay assigned dtolnay and unassigned scottmcm Mar 28, 2025

dtolnay approved these changes Mar 28, 2025

View reviewed changes

Daniel-Aaron-Bloom force-pushed the const_slice_make_iter branch from 4ec741a to beb8e9e Compare March 28, 2025 17:43

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Apr 1, 2025

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 Apr 1, 2025

Zalathar mentioned this pull request Apr 1, 2025

Rollup of 16 pull requests #139203

Closed

Zalathar mentioned this pull request Apr 1, 2025

Rollup of 12 pull requests #139204

Closed

bors added a commit to rust-lang-ci/rust that referenced this pull request Apr 1, 2025

Auto merge of rust-lang#137738 - Daniel-Aaron-Bloom:const_slice_make_…

88dae5c

…iter, r=dtolnay Make slice iterator constructors unstably const See [tracking issue](rust-lang#137737) for justification.

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bors added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Apr 1, 2025

Make slice iterator constructors unstably const

20417a9

Daniel-Aaron-Bloom force-pushed the const_slice_make_iter branch from 7e4cbc4 to 20417a9 Compare April 2, 2025 17:40

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 Apr 2, 2025

bors added the merged-by-bors This PR was explicitly merged by bors. label Apr 3, 2025

bors merged commit e0883a2 into rust-lang:master Apr 3, 2025
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rustbot added this to the 1.88.0 milestone Apr 3, 2025

Daniel-Aaron-Bloom deleted the const_slice_make_iter branch April 3, 2025 15:48

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Make slice iterator constructors unstably const #137738

Make slice iterator constructors unstably const #137738

Daniel-Aaron-Bloom commented Feb 27, 2025 •

edited by tgross35

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Make slice iterator constructors unstably const #137738

Make slice iterator constructors unstably const #137738

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Test differences

Stage 2

Job duration changes

rust-timer commented Apr 3, 2025

Overall result: ❌ regressions - no action needed

Instruction count

Max RSS (memory usage)

Cycles

Binary size

Daniel-Aaron-Bloom commented Feb 27, 2025 •

edited by tgross35

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