Fix vec iter zst alignment #149272

DrAsu33 · 2025-11-24T15:05:24Z

rustbot · 2025-11-24T15:05:27Z

This PR modifies tests/ui/issues/. If this PR is adding new tests to tests/ui/issues/,
please refrain from doing so, and instead add it to more descriptive subdirectories.

rustbot · 2025-11-24T15:05:29Z

r? @fee1-dead

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reddevilmidzy · 2025-11-24T16:39:47Z

tests/ui/issues/issue-zst-nthback-148682.rs

It looks like the file name needs to be changed.

https://rustc-dev-guide.rust-lang.org/tests/best-practices.html#test-naming

Instead of using the issues directory, please refer to this and choose a more appropriate location.

reddevilmidzy · 2025-11-24T16:46:03Z

tests/ui/issues/issue-148682.rs

@@ -0,0 +1,9 @@
+// check-pass


Suggested change

// check-pass

//@ check-pass

Kivooeo · 2025-11-24T23:44:55Z

r? libs

DrAsu33 · 2025-11-25T01:35:08Z

@reddevilmidzy Thanks! Updated as requested.

reddevilmidzy

and please squash

View changes since this review

reddevilmidzy · 2025-11-25T02:19:32Z

tests/ui/issues/issue-zst-nthback-148682.rs

+// @ check-pass
+//test Intolter::nth_back does not cause UB for ZSTs with high alignment


Please remove leading spaces from commands, and add a space before comments.

Suggested change

// @ check-pass

//test Intolter::nth_back does not cause UB for ZSTs with high alignment

//@ check-pass

// test Intolter::nth_back does not cause UB for ZSTs with high alignment

Thanks！It seems that all the CI tests are passed

reddevilmidzy · 2025-11-25T02:23:42Z

tests/ui/issues/issue-zst-nthback-148682.rs

Instead of using the issues directory, please refer to this and choose a more appropriate location.

library/alloc/src/vec/into_iter.rs

reddevilmidzy · 2025-11-25T15:02:39Z

Could you please add close: #148682 to the PR description?(without backtick) GitHub will then automatically close the issue.
and please squash

rustbot · 2025-11-26T00:36:29Z

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.

DrAsu33 · 2025-11-28T01:37:01Z

@rustbot ready

hkBst · 2025-11-28T13:22:20Z

tests/ui/iterators/ZST-nthback.rs

+//@ check-pass
+// test Intolter::nth_back does not cause UB for ZSTs with high alignment
+
+#[repr(align(8))]
+struct Thing;
+
+fn main() {
+    let v = vec![Thing, Thing];
+    let _ = v.into_iter().nth_back(1);
+}


The issue shows a reproduction using Miri, so I'm wondering how this test is supposed to reproduce that. IIUC this does the equivalent of "cargo check", no, while what is needed is a miri check.

workingjubilee · 2025-11-29T06:26:41Z

tests/ui/iterators/ZST-nthback.rs

@@ -0,0 +1,10 @@
+//@ run-pass


This still will not be a test we run under miri, I believe.

We do run the standard library's tests under miri, however.

rustbot · 2025-11-29T07:28:01Z

The Miri subtree was changed

cc @rust-lang/miri

RalfJung

Some comments for the Miri test. :)
I did not look at the libs part.

FWIW, we do run the standard library test suite in Miri. So maybe it would make more sense to add this there? We already have some tests in the standard library test suite that are primarily meant for Miri.

View changes since this review

RalfJung · 2025-11-29T07:39:08Z

src/tools/miri/tests/fail/unaligned_pointers/zst-nthback.rs

Please use lower-case filenames.

RalfJung · 2025-11-29T07:39:24Z

src/tools/miri/tests/fail/unaligned_pointers/ZST-nthback.rs

+//@ compile-flags: -Zmiri-symbolic-alignment-check
+//@ run-pass


Suggested change

//@ compile-flags: -Zmiri-symbolic-alignment-check

//@ run-pass

//@compile-flags: -Zmiri-symbolic-alignment-check

Please follow the conventions of surrounding files.

RalfJung · 2025-11-29T07:40:06Z

src/tools/miri/tests/fail/unaligned_pointers/ZST-nthback.rs

+
+    // The main assertion is that the program runs to completion without Miri reporting UB.


Suggested change

// The main assertion is that the program runs to completion without Miri reporting UB.

This doesn't need to be explicitly stated.

RalfJung · 2025-11-29T07:40:44Z

src/tools/miri/tests/fail/unaligned_pointers/ZST-nthback.rs

+//@ compile-flags: -Zmiri-symbolic-alignment-check
+//@ run-pass
+
+use std::ptr;


What are you importing std::ptr for?

DrAsu33 · 2025-11-29T07:57:58Z

Hello @RalfJung .Thanks for the guidance！But I'm still wondering about where I should place test file. Could you please confirm the exact directory path you'd like me to place the new test file (zst_nth_back.rs)?

RalfJung · 2025-11-29T08:01:41Z

library/alloctests/tests/vec.rs seems like the right place. It's not going to be a new file, just a new test function.

RalfJung · 2025-11-29T09:12:42Z

library/alloctests/tests/vec.rs

+// Regression test for Undefined Behavior (UB) caused by IntoIter::nth_back (#148682)
+// when dealing with high-aligned Zero-Sized Types (ZSTs).
 #[test] 
 #[cfg(miri)] 


Why do you only enable this test in Miri?

Sorry, I thought that the UB could only be detected by miri. I have modified that.

Yeah, only Miri will detect UB. But the test should still pass without Miri, and in particular this enures it gets type-checked.

RalfJung · 2025-11-29T09:20:07Z

Also, please run ./x test tidy --bless before committing. No need to wait for CI for simple tidy issues. :)

This commit consolidates all changes, including the core logic fix for IntoIter::nth_back and the addition of the Miri regression test in `library/alloctests/tests/vec.rs`, to prevent Undefined Behavior (UB) when dealing with highly-aligned Zero-Sized Types.

DrAsu33 · 2025-12-03T07:22:21Z

Builds are green and I've addressed all feedback (moved test to library/alloc/tests/vec.rs).

@rustbot ready

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library/alloc/src/vec/into_iter.rs Outdated Show resolved Hide resolved

Kivooeo changed the title ~~Fix vec iter zst alignment 148682~~ Fix vec iter zst alignment Nov 25, 2025

DrAsu33 force-pushed the fix-vec-iter-zst-alignment-148682 branch from ceb3c6f to 069f53f Compare November 26, 2025 00:36

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DrAsu33 force-pushed the fix-vec-iter-zst-alignment-148682 branch from 069f53f to d94bb76 Compare November 26, 2025 00:39

DrAsu33 requested a review from chenyukang November 26, 2025 01:51

rustbot removed the S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. label Nov 28, 2025

rustbot added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Nov 28, 2025

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DrAsu33 force-pushed the fix-vec-iter-zst-alignment-148682 branch 2 times, most recently from 580eef1 to 1a055d7 Compare November 29, 2025 06:22

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rustbot added has-merge-commits PR has merge commits, merge with caution. S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Nov 29, 2025

DrAsu33 force-pushed the fix-vec-iter-zst-alignment-148682 branch from fd0b327 to 8ef3419 Compare November 29, 2025 07:14

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DrAsu33 force-pushed the fix-vec-iter-zst-alignment-148682 branch from e608b3a to ef2ceec Compare November 29, 2025 11:38

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DrAsu33 force-pushed the fix-vec-iter-zst-alignment-148682 branch from ef2ceec to 89b4b30 Compare November 29, 2025 11:44

DrAsu33 requested a review from hkBst December 4, 2025 14:23

		// @ check-pass
		//test Intolter::nth_back does not cause UB for ZSTs with high alignment

		//@ compile-flags: -Zmiri-symbolic-alignment-check
		//@ run-pass

	//@ compile-flags: -Zmiri-symbolic-alignment-check
	//@ run-pass
	//@compile-flags: -Zmiri-symbolic-alignment-check


		// The main assertion is that the program runs to completion without Miri reporting UB.

Fix vec iter zst alignment #149272

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Fix vec iter zst alignment #149272

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