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Merged
rust-bors merged 1 commit into from
Jul 15, 2026
Merged

Account for async closures when pointing at lifetime in return type #159256

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8 changes: 7 additions & 1 deletion compiler/rustc_borrowck/src/diagnostics/region_name.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -791,12 +791,18 @@ impl<'tcx> MirBorrowckCtxt<'_, '_, 'tcx> {
fn give_name_if_anonymous_region_appears_in_output(&self, fr: RegionVid) -> Option<RegionName> {
let tcx = self.infcx.tcx;

let return_ty = self.regioncx.universal_regions().unnormalized_output_ty;
let mut return_ty = self.regioncx.universal_regions().unnormalized_output_ty;
debug!("give_name_if_anonymous_region_appears_in_output: return_ty = {:?}", return_ty);
if !tcx.any_free_region_meets(&return_ty, |r| r.as_var() == fr) {
return None;
}

if let ty::Coroutine(_, args) = return_ty.kind() {
// When the return type is identified to be `{async closure body}`, we instead care
// about the actual return type of that coroutine.
return_ty = args.as_coroutine().return_ty();
}

let mir_hir_id = self.mir_hir_id();

let (return_span, mir_description, hir_ty) = match tcx.hir_node(mir_hir_id) {
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4 changes: 2 additions & 2 deletions tests/ui/async-await/async-closures/higher-ranked-return.stderr
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Expand Up @@ -2,9 +2,9 @@ error: lifetime may not live long enough
--> $DIR/higher-ranked-return.rs:11:46
|
LL | let x = async move |x: &str| -> &str {
| ________________________________-________----_^
| ________________________________-________-____^
| | | |
| | | return type of async closure `{async closure body@$DIR/higher-ranked-return.rs:11:46: 13:10}` contains a lifetime `'2`
| | | let's call the lifetime of this reference `'2`
| | let's call the lifetime of this reference `'1`
LL | | x
LL | | };
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4 changes: 2 additions & 2 deletions tests/ui/async-await/async-closures/not-lending.stderr
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Expand Up @@ -4,7 +4,7 @@ error: lifetime may not live long enough
LL | let x = async move || -> &String { &s };
| ------------------------ ^^^^^^ returning this value requires that `'1` must outlive `'2`
| | |
| | return type of async closure `{async closure body@$DIR/not-lending.rs:12:42: 12:48}` contains a lifetime `'2`
| | let's call the lifetime of this reference `'2`
| lifetime `'1` represents this closure's body
|
= note: closure implements `AsyncFn`, so references to captured variables can't escape the closure
Expand All @@ -15,7 +15,7 @@ error: lifetime may not live long enough
LL | let x = async move || { &s };
| ------------- ^^^^^^ returning this value requires that `'1` must outlive `'2`
| | |
| | return type of async closure `{async closure body@$DIR/not-lending.rs:16:31: 16:37}` contains a lifetime `'2`
| | return type of async closure is &'2 String
| lifetime `'1` represents this closure's body
|
= note: closure implements `AsyncFn`, so references to captured variables can't escape the closure
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4 changes: 2 additions & 2 deletions tests/ui/async-await/issue-74072-lifetime-name-annotations.stderr
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Expand Up @@ -29,7 +29,7 @@ error: lifetime may not live long enough
LL | (async move || {
| ______-------------_^
| | | |
| | | return type of async closure `{async closure body@$DIR/issue-74072-lifetime-name-annotations.rs:13:20: 19:6}` contains a lifetime `'2`
| | | return type of async closure is &'2 i32
| | lifetime `'1` represents this closure's body
LL | |
LL | |
Expand Down Expand Up @@ -78,7 +78,7 @@ error: lifetime may not live long enough
LL | (async move || -> &i32 {
| ______---------------------_^
| | | |
| | | return type of async closure `{async closure body@$DIR/issue-74072-lifetime-name-annotations.rs:23:28: 29:6}` contains a lifetime `'2`
| | | let's call the lifetime of this reference `'2`
| | lifetime `'1` represents this closure's body
LL | |
LL | |
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