lint ineffective #[unstable] annotations on re-exports by amirHdev · Pull Request #161178 · rust-lang/rust

amirHdev · 2026-08-16T14:49:12Z

rustbot · 2026-08-17T16:53:27Z

rustbot has assigned @mejrs.
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amirHdev · 2026-08-17T16:55:15Z

r? clarfonthey

mejrs · 2026-08-18T11:07:20Z

+        };
+
+        let (has_target, all_targets_stable) = self.classify_reexport_targets(
+            [path.res.type_ns, path.res.value_ns, path.res.macro_ns].into_iter().flatten(),


Suggested change

[path.res.type_ns, path.res.value_ns, path.res.macro_ns].into_iter().flatten(),

path.res.present_items()

View changes since the review

mejrs · 2026-08-18T11:10:30Z

+        for (span, reexport) in &self.unstable_reexports {
+            if reexport.has_target && reexport.all_targets_stable {
+                self.tcx.emit_node_span_lint(
+                    UNUSED_ATTRIBUTES,


Can you make a standalone lint for this, not reuse UNUSED_ATTRIBUTES? And make it deny by default?

It looks like this fix is just a temporary measure, but a proper fix looks hard so I suspect this will end up becoming somewhat permanent.

View changes since the review

mejrs · 2026-08-18T11:32:14Z

+                // Do not emit the lint if resolution is incomplete or the
+                // target cannot be classified.


Can "resolution being incomplete" even happen? And what does "the target cannot be classified" mean?

View changes since the review

I switched this to explicit Res handling

mejrs · 2026-08-18T11:36:54Z

+        let mut all_targets_stable = true;
+
+        for res in targets {
+            let Some(def_id) = res.opt_def_id() else {


I don't think this handles re-exports of primitives correctly. We do have modules that re-export primitives, like std::primitive.

View changes since the review

mejrs · 2026-08-18T11:48:22Z

+    fn unstable_reexport_span(&self, item: &'tcx hir::Item<'tcx>) -> Option<Span> {
+        let attrs = self.tcx.hir_attrs(item.hir_id());
+        let (stability, span) =
+            find_attr!(attrs, Stability { stability, span } => (*stability, *span))?;
+
+        matches!(stability.level, StabilityLevel::Unstable { .. }).then_some(span)
+    }


this span would be more helpful if it pointed to the item being re-exported

View changes since the review

the attribute span is only kept as the grouping key for grouped reexport for now

mejrs

I still need to understand the logic of stability gating better (both what you've added and what's already there), so I'm not done yet

View changes since this review

mejrs · 2026-08-19T11:08:35Z

+declare_lint! {
+    /// The `ineffective_unstable_reexport` lint detects `#[unstable]` attributes
+    /// on re-exports where the attribute does not make the re-exported path unstable.
+    ///
+    /// ### Example
+    ///
+    /// ```rust,compile_fail
+    /// #![feature(staged_api)]
+    /// #![stable(feature = "test", since = "1.0.0")]
+    ///
+    /// #[stable(feature = "test", since = "1.0.0")]
+    /// pub struct S;
+    ///
+    /// #[unstable(feature = "reexport", issue = "none")]
+    /// pub use crate::S as T;
+    ///
+    /// fn main() {}
+    /// ```
+    ///
+    /// {{produces}}
+    ///
+    /// ### Explanation
+    ///
+    /// Stability attributes on re-exports do not currently change the
+    /// stability of an otherwise stable re-exported item.
+    pub INEFFECTIVE_UNSTABLE_REEXPORT,
+    Deny,
+    "detects ineffective `#[unstable]` attributes on re-exports"
+}


Can you also feature gate this lint behind the staged_api feature? and add a feature gate test for it?

(If you can suppress the "use #![feature(staged_api)] .." suggestion that'd be nice - we suppress that suggestion elsewhere as well.)

petrochenkov · 2026-08-19T11:21:54Z

    slice_write_vectored, take,
 };

+pub use self::buf_read::BufRead;


I don't think having publicly reachable items without any stability annotations is a right thing.
The current stability logic is right in at least one thing - it requires stability annotations on everything reachable.
The new behavior should be the same, IMO, it just needs to make sure that the reexport's stability annotation is compatible with the stability that is actually used (stability of that reexport's ultimate definition).
cc #146028 (comment)

View changes since the review

I agree we should keep explicit stability annotations on public re-exports but one concern remains if i am correct. if the intended semantics allow a stable item to be reexported through an unstable path should this lint really reject that case? perhaps the check should only reject reexports that weaken the stability of the ultimate definition

If cases like this are rare, they can use allow(ineffective_unstable_reexport) with a comment.

petrochenkov · 2026-08-19T13:37:43Z

(Also the lint doesn't follow the lint naming conventions - https://rust-lang.github.io/rfcs/0344-conventions-galore.html#lints.)

Signed-off-by: Amirhossein Akhlaghpour <m9.akhlaghpoor@gmail.com>

clarfonthey · 2026-08-29T01:41:02Z


+#[derive(Diagnostic)]
+#[diag("stability annotation on this re-export does not match the re-exported item")]
+pub(crate) struct IncompatibleReexportStability;


It would be nice to provide the spans of the two attributes being checked, but it does appear that these spans aren't retained in the Stability type you seem to be comparing against. So, perhaps as a compromise, simply stating what the two stability attributes were (even debug-printing them) might be helpful in the output.

View changes since the review

Yeah, gonna say that debug-printing is fine for now. Since this is just an internal lint, I think it should be fine to just show raw debug output on an initial version.

One small concern is that storing the format string directly might affect perf, but will run perf before merging anyway.

Sounds good thanks. it works for me and we can revisit the representation if the perf run shows anything concerning

Looks like it's fine

Signed-off-by: Amirhossein Akhlaghpour <m9.akhlaghpoor@gmail.com>

clarfonthey · 2026-08-29T13:27:42Z

@bors try @rust-timer queue

lint ineffective #[unstable] annotations on re-exports

clarfonthey · 2026-08-29T13:29:14Z

Side note: will code review the whole thing, but will probably pass off to compiler for a final review after verifying the functionality is good for libs, since I'm not familiar enough with the lint code to be able to say it's doing things "the right way" in that sense.

rust-bors · 2026-08-29T14:26:56Z

☀️ Try build successful (CI)
Build commit: f3482bf (f3482bfb4828183bd9977b4799330b8c188fc5b6)
Base parent: 6bb812b (6bb812b714cce8e08864b7b569303f25ab08eaad)

rust-timer · 2026-08-29T15:10:14Z

Finished benchmarking commit (f3482bf): comparison URL.

Overall result: ❌✅ regressions and improvements - no action needed

Benchmarking means the PR may be perf-sensitive. Consider adding rollup=never if this change is not fit for rolling up.

@rustbot label: -S-waiting-on-perf -perf-regression

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	0.2%	[0.1%, 0.2%]	5
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.5%	[-0.5%, -0.5%]	1
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results (secondary -4.2%)

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

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-4.2%	[-5.2%, -3.2%]	2
All ❌✅ (primary)	-	-	0

Cycles

Results (secondary 5.6%)

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

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	13.8%	[8.3%, 17.4%]	3
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.6%	[-2.7%, -2.5%]	3
All ❌✅ (primary)	-	-	0

Binary size

This perf run didn't have relevant results for this metric.

Bootstrap: 475.357s -> 474.541s (-0.17%)
Artifact size: 402.87 MiB -> 402.80 MiB (-0.02%)

rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Aug 16, 2026

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amirHdev force-pushed the unstable-reexport branch from 8dd3a1f to 13f91d6 Compare August 16, 2026 14:58

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amirHdev marked this pull request as ready for review August 17, 2026 16:53

rustbot added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Aug 17, 2026

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rustbot assigned clarfonthey and unassigned mejrs Aug 17, 2026

mejrs reviewed Aug 18, 2026

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amirHdev requested a review from mejrs August 18, 2026 14:34

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amirHdev force-pushed the unstable-reexport branch from c1b5930 to 17f1859 Compare August 18, 2026 15:19

mejrs reviewed Aug 19, 2026

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petrochenkov reviewed Aug 19, 2026

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amirHdev requested review from mejrs and petrochenkov August 20, 2026 10:47

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amirHdev added 5 commits August 21, 2026 14:59

lint ineffective #[unstable] annotations on re-exports

79d5626

Signed-off-by: Amirhossein Akhlaghpour <m9.akhlaghpoor@gmail.com>

handle std fallout from unstable re-export lint

7b7695d

Signed-off-by: Amirhossein Akhlaghpour <m9.akhlaghpoor@gmail.com>

allow clippy on unstable re-export suppressions

7249fbc

Signed-off-by: Amirhossein Akhlaghpour <m9.akhlaghpoor@gmail.com>

add dedicated lint for ineffective unstable re-exports

e22c3c2

Signed-off-by: Amirhossein Akhlaghpour <m9.akhlaghpoor@gmail.com>

refine unstable reexport lint

fbec8a6

Signed-off-by: Amirhossein Akhlaghpour <m9.akhlaghpoor@gmail.com>

amirHdev force-pushed the unstable-reexport branch from 790a8ab to fbec8a6 Compare August 21, 2026 12:06

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 Aug 27, 2026

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amirHdev force-pushed the unstable-reexport branch from a78fc29 to 973af67 Compare August 27, 2026 14:33

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amirHdev force-pushed the unstable-reexport branch from 973af67 to 54ae450 Compare August 27, 2026 14:35

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amirHdev force-pushed the unstable-reexport branch from 54ae450 to ef7850c Compare August 27, 2026 18:11

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generalize re-export stability checks

b91102a

Signed-off-by: Amirhossein Akhlaghpour <m9.akhlaghpoor@gmail.com>

amirHdev force-pushed the unstable-reexport branch from ef7850c to b91102a Compare August 28, 2026 10:11

rustbot added O-wasi Operating system: Wasi, Webassembly System Interface O-wasm Target: WASM (WebAssembly), http://webassembly.org/ labels Aug 28, 2026

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fix s390x re-export stability metadata

73e6922

Signed-off-by: Amirhossein Akhlaghpour <m9.akhlaghpoor@gmail.com>

clarfonthey reviewed Aug 29, 2026

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Comment thread compiler/rustc_lint_defs/src/builtin.rs Outdated

clarfonthey reviewed Aug 29, 2026

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fix incompatible reexport stability diagnostics

a246018

Signed-off-by: Amirhossein Akhlaghpour <m9.akhlaghpoor@gmail.com>

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rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Aug 29, 2026

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rust-bors Bot pushed a commit that referenced this pull request Aug 29, 2026

Auto merge of #161178 - amirHdev:unstable-reexport, r=<try>

f3482bf

lint ineffective #[unstable] annotations on re-exports

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	[path.res.type_ns, path.res.value_ns, path.res.macro_ns].into_iter().flatten(),
	path.res.present_items()

		// Do not emit the lint if resolution is incomplete or the
		// target cannot be classified.

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