treat no_mangle_generic_items as hard error instead of lint warning by HerrCai0907 · Pull Request #154585 · rust-lang/rust

HerrCai0907 · 2026-03-30T13:02:53Z

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In rust-lang/miri#4929 (comment), rustc should reject the no_mangled generic function.
This PR treat is as a hard error

HerrCai0907 · 2026-03-30T13:03:12Z

r? @oli-obk

rustbot · 2026-03-30T13:03:18Z

oli-obk is not on the review rotation at the moment.
They may take a while to respond.

oli-obk · 2026-03-30T13:29:40Z

Please make it a hard error and not a lint at all if crater doesn't show any significant regressions.

For crater purposes this works.

oli-obk · 2026-03-30T13:30:08Z

@bors try

set no_mangle_generic_items deny by default

rust-bors · 2026-03-30T15:42:41Z

☀️ Try build successful (CI)
Build commit: ac4c361 (ac4c3613be2acd5395b65d85e5657b81e3c982f0, parent: 4cf5f9580233c36f6bc8db76e282ba8a1c1ea491)

oli-obk · 2026-03-30T17:02:38Z

@craterbot check

craterbot · 2026-03-30T17:03:01Z

👌 Experiment pr-154585 created and queued.
🤖 Automatically detected try build ac4c361
🔍 You can check out the queue and this experiment's details.

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

craterbot · 2026-04-04T18:55:30Z

🚧 Experiment pr-154585 is now running

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

craterbot · 2026-04-06T17:23:19Z

🎉 Experiment pr-154585 is completed!
📊 5 regressed and 2 fixed (871888 total)
📊 5110 spurious results on the retry-regressed-list.txt, consider a retry¹ if this is a significant amount.
📰 Open the summary report.

⚠️ If you notice any spurious failure please add them to the denylist!
ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

re-run the experiment with crates=https://crater-reports.s3.amazonaws.com/pr-154585/retry-regressed-list.txt ↩

RalfJung · 2026-06-24T16:00:21Z

+        assert_contains(&backtrace, "foo", "line-tables-only-helper.rs", 6);
    }
-    assert_contains(&backtrace, "bar", "line-tables-only-helper.rs", 10);
-    assert_contains(&backtrace, "baz", "line-tables-only-helper.rs", 5);
+    assert_contains(&backtrace, "bar", "line-tables-only-helper.rs", 11);
+    assert_contains(&backtrace, "baz", "line-tables-only-helper.rs", 6);


Suggested change

assert_contains(&backtrace, "foo", "line-tables-only-helper.rs", 6);

}

assert_contains(&backtrace, "bar", "line-tables-only-helper.rs", 10);

assert_contains(&backtrace, "baz", "line-tables-only-helper.rs", 5);

assert_contains(&backtrace, "bar", "line-tables-only-helper.rs", 11);

assert_contains(&backtrace, "baz", "line-tables-only-helper.rs", 6);

assert_contains(&backtrace, "foo", "line-tables-only-helper.rs", 12);

}

assert_contains(&backtrace, "bar", "line-tables-only-helper.rs", 8);

assert_contains(&backtrace, "baz", "line-tables-only-helper.rs", 4);

That's based on the CI messages, I'd suggest running the tests locally though.

View changes since the review

traviscross · 2026-06-25T06:05:48Z

Makes sense to me. Thanks @HerrCai0907, @oli-obk, and @RalfJung. I propose we make this a hard error and accept this (minimal) observed breakage.

@rfcbot fcp merge lang

rust-rfcbot · 2026-06-25T06:05:51Z

@traviscross has proposed to merge this. The next step is review by the rest of the tagged team members:

No concerns currently listed.

Once a majority of reviewers approve (and at most 2 approvals are outstanding), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!

cc @rust-lang/lang-advisors: FCP proposed for lang, please feel free to register concerns.
See this document for info about what commands tagged team members can give me.

ehuss · 2026-06-25T13:57:31Z

There is a waiting docs PR at rust-lang/reference#1904. Am I correct that the new rule should state the following?

r[abi.no_mangle.generic]
It is an error to use `no_mangle` on an item with generic type or constant parameters.

RalfJung · 2026-06-25T14:10:00Z

Yes that sounds right. (Though IMO the reference should list where the attribute is allowed, not where it is forbidden.)

tmandry · 2026-07-01T15:10:51Z

@rfcbot reviewed

scottmcm · 2026-07-01T15:11:33Z

Agreed. Obviously can't work and easy to describe the error rule -- easier than giving it a meaning -- so 👍

@rfcbot reviewed

rust-rfcbot · 2026-07-01T15:11:40Z

🔔 This is now entering its final comment period, as per the review above. 🔔

nikomatsakis · 2026-07-01T15:12:28Z

@rfcbot reviewed

rust-rfcbot · 2026-07-11T15:15:23Z

The final comment period, with a disposition to merge, as per the review above, is now complete.

As the automated representative of the governance process, I would like to thank the author for their work and everyone else who contributed.

RalfJung · 2026-07-11T15:36:00Z

@HerrCai0907 could you please rebase, and deal with the CI failures?
All the paperwork for this PR is done, we just have to get the implementation in shape. :)

set no_mangle_generic_items deny by default

3b4b402

rustbot assigned fmease Mar 30, 2026

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rustbot assigned oli-obk and unassigned fmease Mar 30, 2026

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rust-bors Bot pushed a commit that referenced this pull request Mar 30, 2026

Auto merge of #154585 - HerrCai0907:fix/no_mangle_generic_items, r=<try>

ac4c361

set no_mangle_generic_items deny by default

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craterbot added S-waiting-on-crater Status: Waiting on a crater run to be completed. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Mar 30, 2026

fix review

40a9cfe

craterbot removed the S-waiting-on-crater Status: Waiting on a crater run to be completed. label Apr 6, 2026

RalfJung added I-lang-nominated Nominated for discussion during a lang team meeting. S-waiting-on-t-lang Status: Awaiting decision from T-lang labels Jun 24, 2026

RalfJung reviewed Jun 24, 2026

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traviscross added the needs-reference-pr This language change needs an approved Reference PR to proceed. label Jun 25, 2026

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rust-rfcbot added the final-comment-period In the final comment period and will be merged soon unless new substantive objections are raised. label Jul 1, 2026

rust-rfcbot removed the proposed-final-comment-period Proposed to merge/close by relevant subteam, see T-<team> label. Will enter FCP once signed off. label Jul 1, 2026

rustbot mentioned this pull request Jul 11, 2026

Tracking issue for release notes of #154585: treat no_mangle_generic_items as hard error instead of lint warning #159136

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HerrCai0907 commented Mar 30, 2026 •

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