add VecDeque::splice by Qelxiros · Pull Request #147247 · rust-lang/rust

Qelxiros · 2025-10-01T22:30:47Z

Tracking issue: #146975

rustbot · 2025-10-01T22:30:51Z

rustbot has assigned @tgross35.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

antonilol · 2025-10-12T18:58:02Z

Thanks for working on this!

tgross35 · 2025-10-16T22:07:56Z

Sorry I haven't had a chance to look at this, still behind on my reviews

r? libs

bors · 2025-11-01T11:50:12Z

☔ The latest upstream changes (presumably #148337) made this pull request unmergeable. Please resolve the merge conflicts.

library/alloc/src/collections/vec_deque/splice.rs

Mark-Simulacrum · 2025-11-08T16:07:18Z

library/alloc/src/collections/vec_deque/splice.rs

+        // This will set drain.remaining to 0, so its drop won't try to read deallocated memory on
+        // drop.
+        self.drain.by_ref().for_each(drop);
+


Do we need something like

rust/library/alloc/src/vec/splice.rs

Line 62 in 87f9dcd

self.drain.iter = (&[]).iter();

here to avoid problems with Drain::drop?

As I understand it, the for_each will ensure that remaining is set to 0, so Drain::drop won't drop anything. I intentionally use Drain::drop to put the elements together again properly.

library/alloc/src/collections/vec_deque/splice.rs

library/alloc/src/collections/vec_deque/mod.rs

Mark-Simulacrum · 2025-11-08T17:00:55Z

library/alloc/src/collections/vec_deque/splice.rs

+    unsafe fn move_tail(&mut self, additional: usize) {
+        let deque = unsafe { self.deque.as_mut() };
+        let tail_start = deque.len + self.drain_len;
+        deque.buf.reserve(tail_start + self.tail_len, additional);


Do we have coverage for this reserve running? Normally growing VecDeque requires extra logic AFAICT, not just reserving the underlying buffer.

It should run anytime the new iterator (replace_with) has a different length than the removed elements, which is definitely tested. Do you have a more specific case in which this could cause issues?

Qelxiros · 2025-11-17T16:26:03Z

I'm not sure why the CI isn't running, but all the requested changes should be good
@rustbot ready

Mark-Simulacrum · 2025-12-28T18:37:39Z

r=me with a rebase

rustbot · 2025-12-29T18:31:35Z

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.

Qelxiros · 2025-12-29T18:32:48Z

@Mark-Simulacrum should be good, but I don't have permission to r=you.

Mark-Simulacrum · 2025-12-30T19:17:25Z

@bors r+

bors · 2025-12-30T19:17:28Z

📌 Commit 0763954 has been approved by Mark-Simulacrum

It is now in the queue for this repository.

bors · 2025-12-30T19:18:39Z

⌛ Testing commit 0763954 with merge 0e89999...

bors · 2025-12-30T22:39:08Z

☀️ Test successful - checks-actions
Approved by: Mark-Simulacrum
Pushing 0e89999 to main...

github-actions · 2025-12-30T22:41:42Z

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 f0864c8 (parent) -> 0e89999 (this PR)

Test differences

Show 322 test diffs

Stage 1

vec_deque::test_splice: [missing] -> pass (J0)
vec_deque::test_splice_forget: [missing] -> pass (J0)
vec_deque::test_splice_inclusive_out_of_bounds: [missing] -> pass (J0)
vec_deque::test_splice_inclusive_range: [missing] -> pass (J0)
vec_deque::test_splice_inclusive_range2: [missing] -> pass (J0)
vec_deque::test_splice_items_zero_sized: [missing] -> pass (J0)
vec_deque::test_splice_out_of_bounds: [missing] -> pass (J0)
vec_deque::test_splice_unbounded: [missing] -> pass (J0)

Stage 2

vec_deque::test_splice: [missing] -> pass (J1)
vec_deque::test_splice_forget: [missing] -> pass (J1)
vec_deque::test_splice_inclusive_out_of_bounds: [missing] -> pass (J1)
vec_deque::test_splice_inclusive_range: [missing] -> pass (J1)
vec_deque::test_splice_inclusive_range2: [missing] -> pass (J1)
vec_deque::test_splice_items_zero_sized: [missing] -> pass (J1)
vec_deque::test_splice_out_of_bounds: [missing] -> pass (J1)
vec_deque::test_splice_unbounded: [missing] -> pass (J1)

Additionally, 306 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 0e8999942552691afc20495af6227eca8ab0af05 --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-linux: 8820.3s -> 6358.7s (-27.9%)
dist-aarch64-apple: 5676.9s -> 6825.5s (+20.2%)
dist-ohos-armv7: 4115.0s -> 4568.8s (+11.0%)
dist-powerpc64le-linux-musl: 5227.4s -> 5798.1s (+10.9%)
aarch64-msvc-2: 6349.0s -> 5658.2s (-10.9%)
dist-loongarch64-linux: 5321.4s -> 5889.0s (+10.7%)
dist-x86_64-apple: 8164.4s -> 7396.3s (-9.4%)
dist-loongarch64-musl: 5221.9s -> 5703.9s (+9.2%)
dist-apple-various: 4641.9s -> 4246.5s (-8.5%)
x86_64-gnu-llvm-20-1: 4002.2s -> 4324.5s (+8.1%)

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 · 2025-12-30T23:20:35Z

Finished benchmarking commit (0e89999): comparison URL.

Overall result: no relevant changes - no action needed

@rustbot label: -perf-regression

Instruction count

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

Max RSS (memory usage)

Results (primary 4.8%)

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

	mean	range	count
Regressions ❌ (primary)	4.8%	[2.3%, 7.3%]	2
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	4.8%	[2.3%, 7.3%]	2

Cycles

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

Binary size

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

Bootstrap: 481.996s -> 480.336s (-0.34%)
Artifact size: 390.85 MiB -> 390.83 MiB (-0.01%)

rustbot assigned tgross35 Oct 1, 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 Oct 1, 2025

antonilol mentioned this pull request Oct 12, 2025

Tracking Issue for new VecDeque methods prepend, extend_front, splice, extend_from_within and prepend_from_within #146975

Open

9 tasks

rustbot assigned Mark-Simulacrum and unassigned tgross35 Oct 16, 2025

Mark-Simulacrum requested changes Nov 8, 2025

View reviewed changes

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 Nov 8, 2025

Qelxiros force-pushed the vecdeque_splice branch from a9f20e3 to 003ebda Compare November 17, 2025 16:16

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Qelxiros force-pushed the vecdeque_splice branch from 003ebda to f01287c Compare November 17, 2025 16:23

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Qelxiros requested a review from Mark-Simulacrum November 17, 2025 16:25

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 Nov 17, 2025

add VecDeque::splice

0763954

Qelxiros force-pushed the vecdeque_splice branch from f01287c to 0763954 Compare December 29, 2025 18:31

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 Dec 30, 2025

bors added the merged-by-bors This PR was explicitly merged by bors. label Dec 30, 2025

bors merged commit 0e89999 into rust-lang:main Dec 30, 2025
12 checks passed

rustbot added this to the 1.94.0 milestone Dec 30, 2025

This was referenced Dec 30, 2025

Vec::push in consts MVP #147893

Merged

Stabilize alloc_layout_extra #148769

Merged

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Qelxiros commented Nov 17, 2025

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Mark-Simulacrum commented Dec 28, 2025

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Mark-Simulacrum commented Dec 30, 2025

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bors commented Dec 30, 2025

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github-actions bot commented Dec 30, 2025

Test differences

Stage 1

Stage 2

Job duration changes

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rust-timer commented Dec 30, 2025

Overall result: no relevant changes - no action needed

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Qelxiros commented Oct 1, 2025 •

edited by rustbot

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