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Fix false positive for unused_unit #14962

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Merged
merged 2 commits into from
Jun 5, 2025
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Fix false positive for unused_unit #14962

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ed226d2
Fix false positive for unused_unit
Jun 3, 2025
1e96456
Reference correct PR
Jun 3, 2025
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1 change: 1 addition & 0 deletions clippy_lints/src/unused_unit.rs
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Expand Up @@ -109,6 +109,7 @@ impl<'tcx> LateLintPass<'tcx> for UnusedUnit {
&& let AssocItemConstraintKind::Equality { term: Term::Ty(hir_ty) } = constraints[0].kind
&& args.span_ext.hi() != poly.span.hi()
&& !hir_ty.span.from_expansion()
&& args.span_ext.hi() != hir_ty.span.hi()
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@benschulz benschulz Jun 3, 2025 •
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Perhaps this should have been covered by !hir_ty.span.from_expansion(). Certainly, there are no explicit -> () tokens in the source. If this is the case, I'm happy to close this PR and file an issue upstream.

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Those expansion checks are quite finicky; sometimes you have an expression without expansion but a subexpression expanded, etc. So as long as this appears to fix the issue, it's better than nothing.

&& is_unit_ty(hir_ty)
{
lint_unneeded_unit_return(cx, hir_ty.span, poly.span);
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8 changes: 7 additions & 1 deletion tests/ui/unused_unit.edition2021.fixed
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Expand Up @@ -143,4 +143,10 @@ mod issue14577 {
todo!()
}
}
}
}

mod pr14962 {
#[allow(unused_parens)]
type UnusedParensButNoUnit = Box<dyn (Fn())>;
}

8 changes: 7 additions & 1 deletion tests/ui/unused_unit.edition2024.fixed
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Expand Up @@ -143,4 +143,10 @@ mod issue14577 {
todo!()
}
}
}
}

mod pr14962 {
#[allow(unused_parens)]
type UnusedParensButNoUnit = Box<dyn (Fn())>;
}

8 changes: 7 additions & 1 deletion tests/ui/unused_unit.rs
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Expand Up @@ -143,4 +143,10 @@ mod issue14577 {
todo!()
}
}
}
}

mod pr14962 {
#[allow(unused_parens)]
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Since this is a targeted lint, could you please use #[expect(unused_parens)] instead? That doubles as an extra free test for unused_parens that would force us to think about it if its behavior changes.

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This does not actually emit a warning by rustc yet. I'm currently looking into why that is exactly. I can remove the attribute and change the name of the type alias if you want.

type UnusedParensButNoUnit = Box<dyn (Fn())>;
}