set no_mangle_generic_items deny by default#154585

HerrCai0907 · 2026-03-30T13:02:53Z

In rust-lang/miri#4929 (comment), rustc should reject the no_mangled generic function.
This PR change the default behavior from warn to deny.

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 ↩

oli-obk · 2026-04-08T10:13:50Z

I reached out to the jni-mangle author, who used a generic function with no_mangle in a test file, but never actually called it (it wouldn't mangle anyway).

The rxdp failure is because (while there are no generics involved in the function signature) the body uses the generic parameter T from the impl block. (well the failure happens regardless of use in the body, but that's why the functions can't be free functions). I opened a PR to fix it, but the crate also has no dependents, no release in 5 years and the last change to the repo was 3 years ago.

So, let's turn this lint into a hard error. Then we need to write an explainer for T-lang and then we can nominate it.

rustbot · 2026-04-10T05:07:23Z

The Miri subtree was changed

cc @rust-lang/miri

rust-log-analyzer · 2026-04-10T05:40:55Z

The job aarch64-gnu-llvm-21-1 failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

##[endgroup]
Executing "/scripts/stage_2_test_set1.sh"
+ /scripts/stage_2_test_set1.sh
+ '[' 1 == 1 ']'
+ echo 'PR_CI_JOB set; skipping tidy'
+ SKIP_TIDY='--skip tidy'
+ ../x.py --stage 2 test --skip tidy --skip compiler --skip src
PR_CI_JOB set; skipping tidy
##[group]Building bootstrap
    Finished `dev` profile [unoptimized] target(s) in 0.04s
##[endgroup]
---
failures:

---- [ui] tests/ui/backtrace/line-tables-only.rs stdout ----

error: test did not exit with success! code=Some(101) so test would pass with `run-fail`
status: exit status: 101
command: cd "/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/backtrace/line-tables-only" && RUSTC="/checkout/obj/build/aarch64-unknown-linux-gnu/stage2/bin/rustc" RUST_TEST_THREADS="4" "/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/backtrace/line-tables-only/a"
stdout: none
--- stderr -------------------------------
Backtrace [
    { fn: "<std::backtrace::Backtrace>::create" },
    { fn: "line_tables_only_helper::capture_backtrace::{closure#0}", file: "/checkout/tests/ui/backtrace/auxiliary/line-tables-only-helper.rs", line: 17 },
    { fn: "line_tables_only_helper::baz::<line_tables_only_helper::capture_backtrace::{closure#0}>", file: "/checkout/tests/ui/backtrace/auxiliary/line-tables-only-helper.rs", line: 4 },
    { fn: "line_tables_only_helper::bar::<line_tables_only_helper::capture_backtrace::{closure#0}>", file: "/checkout/tests/ui/backtrace/auxiliary/line-tables-only-helper.rs", line: 8 },
    { fn: "line_tables_only_helper::foo::<line_tables_only_helper::capture_backtrace::{closure#0}>", file: "/checkout/tests/ui/backtrace/auxiliary/line-tables-only-helper.rs", line: 12 },
    { fn: "capture_backtrace", file: "/checkout/tests/ui/backtrace/auxiliary/line-tables-only-helper.rs", line: 17 },
    { fn: "main", file: "/checkout/tests/ui/backtrace/line-tables-only.rs", line: 43 },
    { fn: "call_once<fn(), ()>", file: "/rustc/FAKE_PREFIX/library/core/src/ops/function.rs", line: 250 },
    { fn: "__rust_begin_short_backtrace<fn(), ()>", file: "/rustc/FAKE_PREFIX/library/std/src/sys/backtrace.rs", line: 166 },
    { fn: "std::rt::lang_start::<()>::{closure#0}", file: "/rustc/FAKE_PREFIX/library/std/src/rt.rs", line: 206 },
    { fn: "std::rt::lang_start_internal" },
    { fn: "main" },
    { fn: "__libc_start_main" },
    { fn: "_start" },
]
Backtrace [
    { fn: "<std::backtrace::Backtrace>::create" },
    { fn: "line_tables_only_helper::capture_backtrace::{closure#0}", file: "/checkout/tests/ui/backtrace/auxiliary/line-tables-only-helper.rs", line: 17 },
    { fn: "line_tables_only_helper::baz::<line_tables_only_helper::capture_backtrace::{closure#0}>", file: "/checkout/tests/ui/backtrace/auxiliary/line-tables-only-helper.rs", line: 4 },
    { fn: "line_tables_only_helper::bar::<line_tables_only_helper::capture_backtrace::{closure#0}>", file: "/checkout/tests/ui/backtrace/auxiliary/line-tables-only-helper.rs", line: 8 },
    { fn: "line_tables_only_helper::foo::<line_tables_only_helper::capture_backtrace::{closure#0}>", file: "/checkout/tests/ui/backtrace/auxiliary/line-tables-only-helper.rs", line: 12 },
    { fn: "capture_backtrace", file: "/checkout/tests/ui/backtrace/auxiliary/line-tables-only-helper.rs", line: 17 },
    { fn: "main", file: "/checkout/tests/ui/backtrace/line-tables-only.rs", line: 43 },
    { fn: "call_once<fn(), ()>", file: "/rustc/FAKE_PREFIX/library/core/src/ops/function.rs", line: 250 },
    { fn: "__rust_begin_short_backtrace<fn(), ()>", file: "/rustc/FAKE_PREFIX/library/std/src/sys/backtrace.rs", line: 166 },
    { fn: "std::rt::lang_start::<()>::{closure#0}", file: "/rustc/FAKE_PREFIX/library/std/src/rt.rs", line: 206 },
    { fn: "std::rt::lang_start_internal" },
    { fn: "main" },
    { fn: "__libc_start_main" },
    { fn: "_start" },
]

thread 'main' (36099) panicked at /checkout/tests/ui/backtrace/line-tables-only.rs:38:5:
backtrace does not contain expected line 11
stack backtrace:

RalfJung · 2026-04-10T05:59:29Z

src/tools/miri/test-cargo-miri/issue-rust-86261/src/lib.rs

@@ -1,4 +1,4 @@
-#![allow(unused_imports, unused_attributes, no_mangle_generic_items)]


View changes since the review

This looks like we should keep allowing the lint here until this is a hard error.

Oh, the PR title is outdated. It is a hard error now, I see. Please update the PR title and description.

set no_mangle_generic_items deny by default

3b4b402

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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

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oli-obk mentioned this pull request Apr 8, 2026

Remove ineffective no_mangle doyshinda/rxdp#1

Merged

RalfJung reviewed Apr 10, 2026

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		@@ -1,4 +1,4 @@
		#![allow(unused_imports, unused_attributes, no_mangle_generic_items)]

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