10BC0 fix(needless_closure): don't lint on `AsyncFn*`s by ada4a · Pull Request #15649 · rust-lang/rust-clippy · GitHub
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fix(needless_closure): don't lint on AsyncFn*s #15649

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Merged
merged 1 commit into from
Sep 11, 2025
Merged

fix(needless_closure): don't lint on AsyncFn*s #15649

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27 changes: 15 additions & 12 deletions clippy_lints/src/eta_reduction.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -197,6 +197,18 @@ fn check_closure<'tcx>(cx: &LateContext<'tcx>, outer_receiver: Option<&Expr<'tcx
// in a type which is `'static`.
// For now ignore all callee types which reference a type parameter.
&& !generic_args.types().any(|t| matches!(t.kind(), ty::Param(_)))
// Rule out `AsyncFn*`s, because while they can be called as `|x| f(x)`,
// they can't be passed directly into a place expecting an `Fn*` (#13892)
&& let Ok((closure_kind, _)) = cx
.tcx
.infer_ctxt()
.build(cx.typing_mode())
.err_ctxt()
.type_implements_fn_trait(
cx.param_env,
Binder::bind_with_vars(callee_ty_adjusted, List::empty()),
ty::PredicatePolarity::Positive,
)
{
span_lint_hir_and_then(
cx,
10BC0 Expand All @@ -213,19 +225,10 @@ fn check_closure<'tcx>(cx: &LateContext<'tcx>, outer_receiver: Option<&Expr<'tcx
// 'cuz currently nothing changes after deleting this check.
local_used_in(cx, l, args) || local_used_after_expr(cx, l, expr)
}) {
match cx
.tcx
.infer_ctxt()
.build(cx.typing_mode())
.err_ctxt()
.type_implements_fn_trait(
cx.param_env,
Binder::bind_with_vars(callee_ty_adjusted, List::empty()),
ty::PredicatePolarity::Positive,
) {
match closure_kind {
// Mutable closure is used after current expr; we cannot consume it.
Ok((ClosureKind::FnMut, _)) => snippet = format!("&mut {snippet}"),
Ok((ClosureKind::Fn, _)) if !callee_ty_raw.is_ref() => {
ClosureKind::FnMut => snippet = format!("&mut {snippet}"),
ClosureKind::Fn if !callee_ty_raw.is_ref() => {
snippet = format!("&{snippet}");
},
_ => (),
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8 changes: 8 additions & 0 deletions tests/ui/eta.fixed
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Expand Up @@ -635,3 +635,11 @@ fn issue8817() {
//~| HELP: replace the closure with the tuple variant itself
.unwrap(); // just for nicer formatting
}

async fn issue13892<'a, T, F>(maybe: Option<&'a T>, visitor: F)
where
F: AsyncFn(&'a T),
T: 'a,
{
maybe.map(|x| visitor(x));
}
8 changes: 8 additions & 0 deletions tests/ui/eta.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -635,3 +635,11 @@ fn issue8817() {
//~| HELP: replace the closure with the tuple variant itself
.unwrap(); // just for nicer formatting
}

async fn issue13892<'a, T, F>(maybe: Option<&'a T>, visitor: F)
where
F: AsyncFn(&'a T),
T: 'a,
{
maybe.map(|x| visitor(x));
}
0