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Fix unused_parens false positive #143698

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Merged
merged 3 commits into from
Jul 26, 2025
Merged

Fix unused_parens false positive #143698

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e958b20
Fix unused_parens false positive
benschulz Jul 9, 2025
6fc68c1
Add test case for single bound
benschulz Jul 10, 2025
307f664
Replace unwrap_or with explicit match
benschulz Jul 24, 2025
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Fix unused_parens false positive
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@benschulz
benschulz committed Jul 24, 2025
commit e958b20af7ad3e3a053070a9c45389fe463ccc0c
7 changes: 6 additions & 1 deletion compiler/rustc_lint/src/unused.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1062,6 +1062,7 @@ pub(crate) struct UnusedParens {
/// ```
/// type Example = Box<dyn Fn() -> &'static dyn Send>;
/// ```
#[derive(Copy, Clone)]
enum NoBoundsException {
/// The type must be parenthesized.
None,
Expand Down Expand Up @@ -1340,7 +1341,11 @@ impl EarlyLintPass for UnusedParens {
self.with_self_ty_parens = false;
}
ast::TyKind::Ref(_, mut_ty) | ast::TyKind::Ptr(mut_ty) => {
self.in_no_bounds_pos.insert(mut_ty.ty.id, NoBoundsException::OneBound);
// If this type itself appears in no-bounds position, we propagate its
// potentially tighter constraint or risk a false posive (issue 143653).
let own_constraint = self.in_no_bounds_pos.get(&ty.id).copied();
let constraint = own_constraint.unwrap_or(NoBoundsException::OneBound);
self.in_no_bounds_pos.insert(mut_ty.ty.id, constraint);
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in a sense we want tis to be constraint = own_constraint.max(NoBoundsException::OneBound) where as NoBoundsException::OneBound is currently the minimal value this is correct?

I would feel safer if we were to make this a match on own_constraint or add a NoBoundsException.merge function or sth 🤔

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in a sense we want tis to be constraint = own_constraint.max(NoBoundsException::OneBound) where as NoBoundsException::OneBound is currently the minimal value this is correct?

Correct.

I would feel safer if we were to make this a match on own_constraint or add a NoBoundsException.merge function or sth 🤔

I see where you're coming from. I went with the match because 1) I don't see this sprawling and 2) the Option makes the alternatives a bit "messy". Happy to take this any other direction though. 🙂

}
ast::TyKind::TraitObject(bounds, _) | ast::TyKind::ImplTrait(_, bounds) => {
for i in 0..bounds.len() {
Expand Down
9 changes: 9 additions & 0 deletions tests/ui/lint/unused/unused-parens-false-positive-issue-143653.rs
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@@ -0,0 +1,9 @@
//@ check-pass

#![deny(unused_parens)]
#![allow(warnings)]
trait MyTrait {}

fn foo(_: Box<dyn FnMut(&mut u32) -> &mut (dyn MyTrait) + Send + Sync>) {}
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@compiler-errors compiler-errors Jul 9, 2025 •
edited
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How does this behave with dyn FnMut(&()) -> &(dyn Trait) (i.e. one bound that is parenthesized)?

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I've added that case to the test: We continue to emit a warning.


fn main() {}