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use RegionNameHighlight for async fn and closure returns
1 parent 5042dbd commit 61b52a3

7 files changed

+173
-39
lines changed

‎compiler/rustc_mir/src/borrow_check/diagnostics/region_name.rs

+118-34
Original file line numberDiff line numberDiff line change
@@ -6,8 +6,8 @@ use rustc_hir::def::{DefKind, Res};
66
use rustc_middle::ty::print::RegionHighlightMode;
77
use rustc_middle::ty::subst::{GenericArgKind, SubstsRef};
88
use rustc_middle::ty::{self, RegionVid, Ty};
9-
use rustc_span::symbol::kw;
10-
use rustc_span::{symbol::Symbol, Span, DUMMY_SP};
9+
use rustc_span::symbol::{kw, sym, Ident, Symbol};
10+
use rustc_span::{Span, DUMMY_SP};
1111

1212
use crate::borrow_check::{nll::ToRegionVid, universal_regions::DefiningTy, MirBorrowckCtxt};
1313

@@ -39,7 +39,7 @@ crate enum RegionNameSource {
3939
/// The region corresponding to a closure upvar.
4040
AnonRegionFromUpvar(Span, String),
4141
/// The region corresponding to the return type of a closure.
42-
AnonRegionFromOutput(Span, String, String),
42+
AnonRegionFromOutput(RegionNameHighlight, String),
4343
/// The region from a type yielded by a generator.
4444
AnonRegionFromYieldTy(Span, String),
4545
/// An anonymous region from an async fn.
@@ -85,10 +85,10 @@ impl RegionName {
8585
| RegionNameSource::NamedFreeRegion(span)
8686
| RegionNameSource::SynthesizedFreeEnvRegion(span, _)
8787
| RegionNameSource::AnonRegionFromUpvar(span, _)
88-
| RegionNameSource::AnonRegionFromOutput(span, _, _)
8988
| RegionNameSource::AnonRegionFromYieldTy(span, _)
9089
| RegionNameSource::AnonRegionFromAsyncFn(span) => Some(span),
91-
RegionNameSource::AnonRegionFromArgument(ref highlight) => match *highlight {
90+
RegionNameSource::AnonRegionFromArgument(ref highlight)
91+
| RegionNameSource::AnonRegionFromOutput(ref highlight, _) => match *highlight {
9292
RegionNameHighlight::MatchedHirTy(span)
9393
| RegionNameHighlight::MatchedAdtAndSegment(span)
9494
| RegionNameHighlight::CannotMatchHirTy(span, _)
@@ -117,6 +117,7 @@ impl RegionName {
117117
diag.span_label(*span, format!("has type `{}`", type_name));
118118
}
119119
RegionNameSource::AnonRegionFromArgument(RegionNameHighlight::MatchedHirTy(span))
120+
| RegionNameSource::AnonRegionFromOutput(RegionNameHighlight::MatchedHirTy(span), _)
120121
| RegionNameSource::AnonRegionFromAsyncFn(span) => {
121122
diag.span_label(
122123
*span,
@@ -125,6 +126,10 @@ impl RegionName {
125126
}
126127
RegionNameSource::AnonRegionFromArgument(
127128
RegionNameHighlight::MatchedAdtAndSegment(span),
129+
)
130+
| RegionNameSource::AnonRegionFromOutput(
131+
RegionNameHighlight::MatchedAdtAndSegment(span),
132+
_,
128133
) => {
129134
diag.span_label(*span, format!("let's call this `{}`", self));
130135
}
@@ -137,13 +142,28 @@ impl RegionName {
137142
format!("lifetime `{}` appears in the type {}", self, type_name),
138143
);
139144
}
145+
RegionNameSource::AnonRegionFromOutput(
146+
RegionNameHighlight::Occluded(span, type_name),
147+
mir_description,
148+
) => {
149+
diag.span_label(
150+
*span,
151+
format!(
152+
"return type{} `{}` contains a lifetime `{}`",
153+
mir_description, type_name, self
154+
),
155+
);
156+
}
140157
RegionNameSource::AnonRegionFromUpvar(span, upvar_name) => {
141158
diag.span_label(
142159
*span,
143160
format!("lifetime `{}` appears in the type of `{}`", self, upvar_name),
144161
);
145162
}
146-
RegionNameSource::AnonRegionFromOutput(span, mir_description, type_name) => {
163+
RegionNameSource::AnonRegionFromOutput(
164+
RegionNameHighlight::CannotMatchHirTy(span, type_name),
165+
mir_description,
166+
) => {
147167
diag.span_label(*span, format!("return type{} is {}", mir_description, type_name));
148168
}
149169
RegionNameSource::AnonRegionFromYieldTy(span, type_name) => {
@@ -659,67 +679,131 @@ impl<'tcx> MirBorrowckCtxt<'_, 'tcx> {
659679
/// or be early bound (named, not in argument).
660680
fn give_name_if_anonymous_region_appears_in_output(&self, fr: RegionVid) -> Option<RegionName> {
661681
let tcx = self.infcx.tcx;
682+
let hir = tcx.hir();
662683

663684
let return_ty = self.regioncx.universal_regions().unnormalized_output_ty;
664685
debug!("give_name_if_anonymous_region_appears_in_output: return_ty = {:?}", return_ty);
665686
if !tcx.any_free_region_meets(&return_ty, |r| r.to_region_vid() == fr) {
666687
return None;
667688
}
668689

669-
let mut highlight = RegionHighlightMode::default();
670-
highlight.highlighting_region_vid(fr, *self.next_region_name.try_borrow().unwrap());
671-
let type_name =
672-
self.infcx.extract_inference_diagnostics_data(return_ty.into(), Some(highlight)).name;
690+
let mir_hir_id = self.mir_hir_id();
673691

674-
let (return_span, mir_description) = match tcx.hir().get(self.mir_hir_id()) {
692+
let (return_span, mir_description, hir_ty) = match hir.get(mir_hir_id) {
675693
hir::Node::Expr(hir::Expr {
676694
kind: hir::ExprKind::Closure(_, return_ty, body_id, span, _),
677695
..
678696
}) => {
679-
let mut span = match return_ty.output {
680-
hir::FnRetTy::DefaultReturn(_) => tcx.sess.source_map().end_point(*span),
681-
hir::FnRetTy::Return(_) => return_ty.output.span(),
697+
let (mut span, mut hir_ty) = match return_ty.output {
698+
hir::FnRetTy::DefaultReturn(_) => {
699+
(tcx.sess.source_map().end_point(*span), None)
700+
}
701+
hir::FnRetTy::Return(hir_ty) => (return_ty.output.span(), Some(hir_ty)),
682702
};
683-
let mir_description = match tcx.hir().body(*body_id).generator_kind {
703+
let mir_description = match hir.body(*body_id).generator_kind {
684704
Some(hir::GeneratorKind::Async(gen)) => match gen {
685705
hir::AsyncGeneratorKind::Block => " of async block",
686706
hir::AsyncGeneratorKind::Closure => " of async closure",
687707
hir::AsyncGeneratorKind::Fn => {
688-
span = tcx
689-
.hir()
690-
.get(tcx.hir().get_parent_item(mir_hir_id))
708+
let parent_item = hir.get(hir.get_parent_item(mir_hir_id));
709+
let output = &parent_item
691710
.fn_decl()
692711
.expect("generator lowered from async fn should be in fn")
693-
.output
694-
.span();
712+
.output;
713+
span = output.span();
714+
if let hir::FnRetTy::Return(ret) = output {
715+
hir_ty = Some(self.get_future_inner_return_ty(*ret));
716+
}
695717
" of async function"
696718
}
697719
},
698720
Some(hir::GeneratorKind::Gen) => " of generator",
699721
None => " of closure",
700722
};
701-
(span, mir_description)
723+
(span, mir_description, hir_ty)
702724
}
703-
hir::Node::ImplItem(hir::ImplItem {
704-
kind: hir::ImplItemKind::Fn(method_sig, _),
705-
..
706-
}) => (method_sig.decl.output.span(), ""),
707-
_ => (self.body.span, ""),
725+
node => match node.fn_decl() {
726+
Some(fn_decl) => {
727+
let hir_ty = match fn_decl.output {
728+
hir::FnRetTy::DefaultReturn(_) => None,
729+
hir::FnRetTy::Return(ty) => Some(ty),
730+
};
731+
(fn_decl.output.span(), "", hir_ty)
732+
}
733+
None => (self.body.span, "", None),
734+
},
708735
};
709736

737+
let highlight = hir_ty
738+
.and_then(|hir_ty| self.highlight_if_we_can_match_hir_ty(fr, return_ty, hir_ty))
739+
.unwrap_or_else(|| {
740+
// `highlight_if_we_cannot_match_hir_ty` needs to know the number we will give to
741+
// the anonymous region. If it succeeds, the `synthesize_region_name` call below
742+
// will increment the counter, "reserving" the number we just used.
743+
let counter = *self.next_region_name.try_borrow().unwrap();
744+
self.highlight_if_we_cannot_match_hir_ty(fr, return_ty, return_span, counter)
745+
});
746+
710747
Some(RegionName {
711-
// This counter value will already have been used, so this function will increment it
712-
// so the next value will be used next and return the region name that would have been
713-
// used.
714748
name: self.synthesize_region_name(),
715-
source: RegionNameSource::AnonRegionFromOutput(
716-
return_span,
717-
mir_description.to_string(),
718-
type_name,
719-
),
749+
source: RegionNameSource::AnonRegionFromOutput(highlight, mir_description.to_string()),
720750
})
721751
}
722752

753+
/// From the [`hir::Ty`] of an async function's lowered return type,
754+
/// retrieve the `hir::Ty` representing the type the user originally wrote.
755+
///
756+
/// e.g. given the function:
757+
///
758+
/// ```
759+
/// async fn foo() -> i32 {}
760+
/// ```
761+
///
762+
/// this function, given the lowered return type of `foo`, an [`OpaqueDef`] that implements `Future<Output=i32>`,
763+
/// returns the `i32`.
764+
///
765+
/// [`OpaqueDef`]: hir::TyKind::OpaqueDef
766+
fn get_future_inner_return_ty(&self, hir_ty: &'tcx hir::Ty<'tcx>) -> &'tcx hir::Ty<'tcx> {
767+
let hir = self.infcx.tcx.hir();
768+
769+
if let hir::TyKind::OpaqueDef(id, _) = hir_ty.kind {
770+
let opaque_ty = hir.item(id.id);
771+
if let hir::ItemKind::OpaqueTy(hir::OpaqueTy {
772+
bounds:
773+
[hir::GenericBound::LangItemTrait(
774+
hir::LangItem::Future,
775+
_,
776+
_,
777+
hir::GenericArgs {
778+
bindings:
779+
[hir::TypeBinding {
780+
ident: Ident { name: sym::Output, .. },
781+
kind: hir::TypeBindingKind::Equality { ty },
782+
..
783+
}],
784+
..
785+
},
786+
)],
787+
..
788+
}) = opaque_ty.kind
789+
{
790+
ty
791+
} else {
792+
span_bug!(
793+
hir_ty.span,
794+
"bounds from lowered return type of async fn did not match expected format: {:?}",
795+
opaque_ty
796+
);
797+
}
798+
} else {
799+
span_bug!(
800+
hir_ty.span,
801+
"lowered return type of async fn is not OpaqueDef: {:?}",
802+
hir_ty
803+
);
804+
}
805+
}
806+
723807
fn give_name_if_anonymous_region_appears_in_yield_ty(
724808
&self,
725809
fr: RegionVid,

‎src/test/ui/async-await/issue-74072-lifetime-name-annotations.rs

+8
Original file line numberDiff line numberDiff line change
@@ -18,6 +18,14 @@ pub fn async_closure(x: &mut i32) -> impl Future<Output=&i32> {
1818
})()
1919
}
2020

21+
pub fn async_closure_explicit_return_type(x: &mut i32) -> impl Future<Output=&i32> {
22+
(async move || -> &i32 {
23+
let y = &*x;
24+
*x += 1; //~ ERROR cannot assign to `*x` because it is borrowed
25+
y
26+
})()
27+
}
28+
2129
pub fn async_block(x: &mut i32) -> impl Future<Output=&i32> {
2230
async move {
2331
let y = &*x;

‎src/test/ui/async-await/issue-74072-lifetime-name-annotations.stderr

+14-2
Original file line numberDiff line numberDiff line change
@@ -2,7 +2,7 @@ error[E0506]: cannot assign to `*x` because it is borrowed
22
--> $DIR/issue-74072-lifetime-name-annotations.rs:9:5
33
|
44
LL | pub async fn async_fn(x: &mut i32) -> &i32 {
5-
| ---- return type of async function is &'1 i32
5+
| - let's call the lifetime of this reference `'1`
66
LL | let y = &*x;
77
| --- borrow of `*x` occurs here
88
LL | *x += 1;
@@ -25,6 +25,18 @@ LL | })()
2525
error[E0506]: cannot assign to `*x` because it is borrowed
2626
--> $DIR/issue-74072-lifetime-name-annotations.rs:24:9
2727
|
28+
LL | (async move || -> &i32 {
29+
| - let's call the lifetime of this reference `'1`
30+
LL | let y = &*x;
31+
| --- borrow of `*x` occurs here
32+
LL | *x += 1;
33+
| ^^^^^^^ assignment to borrowed `*x` occurs here
34+
LL | y
35+
| - returning this value requires that `*x` is borrowed for `'1`
36+
37+
error[E0506]: cannot assign to `*x` because it is borrowed
38+
--> $DIR/issue-74072-lifetime-name-annotations.rs:32:9
39+
|
2840
LL | let y = &*x;
2941
| --- borrow of `*x` occurs here
3042
LL | *x += 1;
@@ -34,6 +46,6 @@ LL | y
3446
LL | }
3547
| - return type of async block is &'1 i32
3648

37-
error: aborting due to 3 previous errors
49+
error: aborting due to 4 previous errors
3850

3951
For more information about this error, try `rustc --explain E0506`.

‎src/test/ui/async-await/issue-74497-lifetime-in-opaque.rs

+19
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,19 @@
1+
// edition:2018
2+
3+
// test that names give to anonymous lifetimes in opaque types like `impl Future` are correctly
4+
// introduced in error messages
5+
6+
use std::future::Future;
7+
8+
pub async fn foo<F, T>(_: F)
9+
where
10+
F: Fn(&u8) -> T,
11+
T: Future<Output = ()>,
12+
{
13+
}
14+
15+
pub async fn bar(_: &u8) {}
16+
17+
fn main() {
18+
let _ = foo(|x| bar(x)); //~ ERROR lifetime may not live long enough
19+
}

‎src/test/ui/async-await/issue-74497-lifetime-in-opaque.stderr

+11
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,11 @@
1+
error: lifetime may not live long enough
2+
--> $DIR/issue-74497-lifetime-in-opaque.rs:18:21
3+
|
4+
LL | let _ = foo(|x| bar(x));
5+
| -- ^^^^^^ returning this value requires that `'1` must outlive `'2`
6+
| ||
7+
| |return type of closure `impl Future` contains a lifetime `'2`
8+
| has type `&'1 u8`
9+
10+
error: aborting due to previous error
11+

‎src/test/ui/borrowck/issue-53432-nested-closure-outlives-borrowed-value.stderr

+1-1
Original file line numberDiff line numberDiff line change
@@ -4,7 +4,7 @@ error: lifetime may not live long enough
44
LL | let _action = move || {
55
| -------
66
| | |
7-
| | return type of closure is [closure@$DIR/issue-53432-nested-closure-outlives-borrowed-value.rs:4:9: 4:15]
7+
| | return type of closure `[closure@$DIR/issue-53432-nested-closure-outlives-borrowed-value.rs:4:9: 4:15]` contains a lifetime `'2`
88
| lifetime `'1` represents this closure's body
99
LL | || f() // The `nested` closure
1010
| ^^^^^^ returning this value requires that `'1` must outlive `'2`

‎src/test/ui/nll/issue-58053.stderr

+2-2
Original file line numberDiff line numberDiff line change
@@ -2,9 +2,9 @@ error: lifetime may not live long enough
22
--> $DIR/issue-58053.rs:6:33
33
|
44
LL | let f = |x: &i32| -> &i32 { x };
5-
| - ---- ^ returning this value requires that `'1` must outlive `'2`
5+
| - - ^ returning this value requires that `'1` must outlive `'2`
66
| | |
7-
| | return type of closure is &'2 i32
7+
| | let's call the lifetime of this reference `'2`
88
| let's call the lifetime of this reference `'1`
99

1010
error: lifetime may not live long enough

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