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Add some extra information to opaque type cycle errors
1 parent 66ae999 commit 9e98feb

16 files changed

+421
-24
lines changed

‎compiler/rustc_middle/src/traits/mod.rs

+4
Original file line numberDiff line numberDiff line change
@@ -588,6 +588,10 @@ pub enum SelectionError<'tcx> {
588588
/// Signaling that an error has already been emitted, to avoid
589589
/// multiple errors being shown.
590590
ErrorReporting,
591+
/// Computing an opaque type's hidden type caused an error (e.g. a cycle error).
592+
/// We can thus not know whether the hidden type implements an auto trait, so
593+
/// we should not presume anything about it.
594+
OpaqueTypeAutoTraitLeakageUnknown(DefId),
591595
}
592596

593597
#[derive(Clone, Debug, TypeVisitable, Lift)]

‎compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs

+45-1
Original file line numberDiff line numberDiff line change
@@ -30,7 +30,7 @@ use rustc_infer::infer::error_reporting::TypeErrCtxt;
3030
use rustc_infer::infer::{InferOk, TypeTrace};
3131
use rustc_middle::traits::select::OverflowError;
3232
use rustc_middle::traits::solve::Goal;
33-
use rustc_middle::traits::SelectionOutputTypeParameterMismatch;
33+
use rustc_middle::traits::{DefiningAnchor, SelectionOutputTypeParameterMismatch};
3434
use rustc_middle::ty::abstract_const::NotConstEvaluatable;
3535
use rustc_middle::ty::error::{ExpectedFound, TypeError};
3636
use rustc_middle::ty::fold::{TypeFolder, TypeSuperFoldable};
@@ -1152,6 +1152,11 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
11521152
}
11531153
}
11541154

1155+
SelectionError::OpaqueTypeAutoTraitLeakageUnknown(def_id) => self.report_opaque_type_auto_trait_leakage(
1156+
&obligation,
1157+
def_id,
1158+
),
1159+
11551160
TraitNotObjectSafe(did) => {
11561161
let violations = self.tcx.object_safety_violations(did);
11571162
report_object_safety_error(self.tcx, span, did, violations)
@@ -1465,6 +1470,12 @@ trait InferCtxtPrivExt<'tcx> {
14651470
terr: TypeError<'tcx>,
14661471
) -> DiagnosticBuilder<'tcx, ErrorGuaranteed>;
14671472

1473+
fn report_opaque_type_auto_trait_leakage(
1474+
&self,
1475+
obligation: &PredicateObligation<'tcx>,
1476+
def_id: DefId,
1477+
) -> DiagnosticBuilder<'tcx, ErrorGuaranteed>;
1478+
14681479
fn report_type_parameter_mismatch_error(
14691480
&self,
14701481
obligation: &PredicateObligation<'tcx>,
@@ -3186,6 +3197,39 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
31863197
)
31873198
}
31883199

3200+
fn report_opaque_type_auto_trait_leakage(
3201+
&self,
3202+
obligation: &PredicateObligation<'tcx>,
3203+
def_id: DefId,
3204+
) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
3205+
let name = match self.tcx.opaque_type_origin(def_id.expect_local()) {
3206+
hir::OpaqueTyOrigin::FnReturn(_) | hir::OpaqueTyOrigin::AsyncFn(_) => {
3207+
format!("opaque type")
3208+
}
3209+
hir::OpaqueTyOrigin::TyAlias { .. } => {
3210+
format!("`{}`", self.tcx.def_path_debug_str(def_id))
3211+
}
3212+
};
3213+
let mut err = self.tcx.sess.struct_span_err(
3214+
obligation.cause.span,
3215+
format!("cannot check whether the hidden type of {name} satisfies auto traits"),
3216+
);
3217+
err.span_note(self.tcx.def_span(def_id), "opaque type is declared here");
3218+
match self.defining_use_anchor {
3219+
DefiningAnchor::Bubble | DefiningAnchor::Error => {}
3220+
DefiningAnchor::Bind(bind) => {
3221+
err.span_note(
3222+
self.tcx.def_ident_span(bind).unwrap_or_else(|| self.tcx.def_span(bind)),
3223+
"this item depends on auto traits of the hidden type, \
3224+
but may also be registering the hidden type. \
3225+
This is not supported right now. \
3226+
You can try moving the opaque type and the item that actually registers a hidden type into a new submodule".to_string(),
3227+
);
3228+
}
3229+
};
3230+
err
3231+
}
3232+
31893233
fn report_type_parameter_mismatch_error(
31903234
&self,
31913235
obligation: &PredicateObligation<'tcx>,

‎compiler/rustc_trait_selection/src/traits/select/confirmation.rs

+4-4
Original file line numberDiff line numberDiff line change
@@ -67,7 +67,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
6767
}
6868

6969
AutoImplCandidate => {
70-
let data = self.confirm_auto_impl_candidate(obligation);
70+
let data = self.confirm_auto_impl_candidate(obligation)?;
7171
ImplSource::Builtin(data)
7272
}
7373

@@ -376,12 +376,12 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
376376
fn confirm_auto_impl_candidate(
377377
&mut self,
378378
obligation: &TraitObligation<'tcx>,
379-
) -> Vec<PredicateObligation<'tcx>> {
379+
) -> Result<Vec<PredicateObligation<'tcx>>, SelectionError<'tcx>> {
380380
debug!(?obligation, "confirm_auto_impl_candidate");
381381

382382
let self_ty = self.infcx.shallow_resolve(obligation.predicate.self_ty());
383-
let types = self.constituent_types_for_ty(self_ty);
384-
self.vtable_auto_impl(obligation, obligation.predicate.def_id(), types)
383+
let types = self.constituent_types_for_ty(self_ty)?;
384+
Ok(self.vtable_auto_impl(obligation, obligation.predicate.def_id(), types))
385385
}
386386

387387
/// See `confirm_auto_impl_candidate`.

‎compiler/rustc_trait_selection/src/traits/select/mod.rs

+8-4
Original file line numberDiff line numberDiff line change
@@ -2294,8 +2294,8 @@ impl<'tcx> SelectionContext<'_, 'tcx> {
22942294
fn constituent_types_for_ty(
22952295
&self,
22962296
t: ty::Binder<'tcx, Ty<'tcx>>,
2297-
) -> ty::Binder<'tcx, Vec<Ty<'tcx>>> {
2298-
match *t.skip_binder().kind() {
2297+
) -> Result<ty::Binder<'tcx, Vec<Ty<'tcx>>>, SelectionError<'tcx>> {
2298+
Ok(match *t.skip_binder().kind() {
22992299
ty::Uint(_)
23002300
| ty::Int(_)
23012301
| ty::Bool
@@ -2359,12 +2359,16 @@ impl<'tcx> SelectionContext<'_, 'tcx> {
23592359
}
23602360

23612361
ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs, .. }) => {
2362+
let ty = self.tcx().type_of(def_id);
2363+
if ty.skip_binder().references_error() {
2364+
return Err(SelectionError::OpaqueTypeAutoTraitLeakageUnknown(def_id));
2365+
}
23622366
// We can resolve the `impl Trait` to its concrete type,
23632367
// which enforces a DAG between the functions requiring
23642368
// the auto trait bounds in question.
2365-
t.rebind(vec![self.tcx().type_of(def_id).subst(self.tcx(), substs)])
2369+
t.rebind(vec![ty.subst(self.tcx(), substs)])
23662370
}
2367-
}
2371+
})
23682372
}
23692373

23702374
fn collect_predicates_for_types(

‎tests/ui/generator/layout-error.rs

+1
Original file line numberDiff line numberDiff line change
@@ -24,5 +24,6 @@ fn main() {
2424
type F = impl Future;
2525
// Check that statics are inhabited computes they layout.
2626
static POOL: Task<F> = Task::new();
27+
//~^ ERROR: cannot check whether the hidden type of `layout_error[b009]::main::F::{opaque#0}` satisfies auto traits
2728
Task::spawn(&POOL, || cb());
2829
}

‎tests/ui/generator/layout-error.stderr

+19-1
Original file line numberDiff line numberDiff line change
@@ -4,6 +4,24 @@ error[E0425]: cannot find value `Foo` in this scope
44
LL | let a = Foo;
55
| ^^^ not found in this scope
66

7-
error: aborting due to previous error
7+
error: cannot check whether the hidden type of `layout_error[b009]::main::F::{opaque#0}` satisfies auto traits
8+
--> $DIR/layout-error.rs:26:18
9+
|
10+
LL | static POOL: Task<F> = Task::new();
11+
| ^^^^^^^
12+
|
13+
note: opaque type is declared here
14+
--> $DIR/layout-error.rs:24:14
15+
|
16+
LL | type F = impl Future;
17+
| ^^^^^^^^^^^
18+
note: required because it appears within the type `Task<F>`
19+
--> $DIR/layout-error.rs:9:12
20+
|
21+
LL | pub struct Task<F: Future>(F);
22+
| ^^^^
23+
= note: shared static variables must have a type that implements `Sync`
24+
25+
error: aborting due to 2 previous errors
826

927
For more information about this error, try `rustc --explain E0425`.

‎tests/ui/impl-trait/auto-trait-leak.rs

+4-2
Original file line numberDiff line numberDiff line change
@@ -3,21 +3,23 @@ use std::rc::Rc;
33

44
fn send<T: Send>(_: T) {}
55

6-
fn main() {
7-
}
6+
fn main() {}
87

98
// Cycles should work as the deferred obligations are
109
// independently resolved and only require the concrete
1110
// return type, which can't depend on the obligation.
1211
fn cycle1() -> impl Clone {
1312
//~^ ERROR cycle detected
13+
//~| ERROR cycle detected
1414
send(cycle2().clone());
15+
//~^ ERROR: cannot check whether the hidden type of opaque type satisfies auto traits
1516

1617
Rc::new(Cell::new(5))
1718
}
1819

1920
fn cycle2() -> impl Clone {
2021
send(cycle1().clone());
22+
//~^ ERROR: cannot check whether the hidden type of opaque type satisfies auto traits
2123

2224
Rc::new(String::from("foo"))
2325
}

‎tests/ui/impl-trait/auto-trait-leak.stderr

+87-4
Original file line numberDiff line numberDiff line change
@@ -1,5 +1,5 @@
11
error[E0391]: cycle detected when computing type of `cycle1::{opaque#0}`
2-
--> $DIR/auto-trait-leak.rs:12:16
2+
--> $DIR/auto-trait-leak.rs:11:16
33
|
44
LL | fn cycle1() -> impl Clone {
55
| ^^^^^^^^^^
@@ -11,12 +11,12 @@ LL | send(cycle2().clone());
1111
| ^^^^
1212
= note: ...which requires evaluating trait selection obligation `cycle2::{opaque#0}: core::marker::Send`...
1313
note: ...which requires computing type of `cycle2::{opaque#0}`...
14-
--> $DIR/auto-trait-leak.rs:19:16
14+
--> $DIR/auto-trait-leak.rs:20:16
1515
|
1616
LL | fn cycle2() -> impl Clone {
1717
| ^^^^^^^^^^
1818
note: ...which requires type-checking `cycle2`...
19-
--> $DIR/auto-trait-leak.rs:20:5
19+
--> $DIR/auto-trait-leak.rs:21:5
2020
|
2121
LL | send(cycle1().clone());
2222
| ^^^^
@@ -34,6 +34,89 @@ LL | | Rc::new(String::from("foo"))
3434
LL | | }
3535
| |_^
3636

37-
error: aborting due to previous error
37+
error[E0391]: cycle detected when computing type of `cycle1::{opaque#0}`
38+
--> $DIR/auto-trait-leak.rs:11:16
39+
|
40+
LL | fn cycle1() -> impl Clone {
41+
| ^^^^^^^^^^
42+
|
43+
note: ...which requires type-checking `cycle1`...
44+
--> $DIR/auto-trait-leak.rs:14:5
45+
|
46+
LL | send(cycle2().clone());
47+
| ^^^^
48+
= note: ...which requires evaluating trait selection obligation `cycle2::{opaque#0}: core::marker::Send`...
49+
note: ...which requires computing type of `cycle2::{opaque#0}`...
50+
--> $DIR/auto-trait-leak.rs:20:16
51+
|
52+
LL | fn cycle2() -> impl Clone {
53+
| ^^^^^^^^^^
54+
note: ...which requires type-checking `cycle2`...
55+
--> $DIR/auto-trait-leak.rs:20:1
56+
|
57+
LL | fn cycle2() -> impl Clone {
58+
| ^^^^^^^^^^^^^^^^^^^^^^^^^
59+
= note: ...which again requires computing type of `cycle1::{opaque#0}`, completing the cycle
60+
note: cycle used when checking item types in top-level module
61+
--> $DIR/auto-trait-leak.rs:1:1
62+
|
63+
LL | / use std::cell::Cell;
64+
LL | | use std::rc::Rc;
65+
LL | |
66+
LL | | fn send<T: Send>(_: T) {}
67+
... |
68+
LL | | Rc::new(String::from("foo"))
69+
LL | | }
70+
| |_^
71+
72+
error: cannot check whether the hidden type of opaque type satisfies auto traits
73+
--> $DIR/auto-trait-leak.rs:21:10
74+
|
75+
LL | send(cycle1().clone());
76+
| ---- ^^^^^^^^^^^^^^^^
77+
| |
78+
| required by a bound introduced by this call
79+
|
80+
note: opaque type is declared here
81+
--> $DIR/auto-trait-leak.rs:11:16
82+
|
83+
LL | fn cycle1() -> impl Clone {
84+
| ^^^^^^^^^^
85+
note: this item depends on auto traits of the hidden type, but may also be registering the hidden type. This is not supported right now. You can try moving the opaque type and the item that actually registers a hidden type into a new submodule
86+
--> $DIR/auto-trait-leak.rs:20:4
87+
|
88+
LL | fn cycle2() -> impl Clone {
89+
| ^^^^^^
90+
note: required by a bound in `send`
91+
--> $DIR/auto-trait-leak.rs:4:12
92+
|
93+
LL | fn send<T: Send>(_: T) {}
94+
| ^^^^ required by this bound in `send`
95+
96+
error: cannot check whether the hidden type of opaque type satisfies auto traits
97+
--> $DIR/auto-trait-leak.rs:14:10
98+
|
99+
LL | send(cycle2().clone());
100+
| ---- ^^^^^^^^^^^^^^^^
101+
| |
102+
| required by a bound introduced by this call
103+
|
104+
note: opaque type is declared here
105+
--> $DIR/auto-trait-leak.rs:20:16
106+
|
107+
LL | fn cycle2() -> impl Clone {
108+
| ^^^^^^^^^^
109+
note: this item depends on auto traits of the hidden type, but may also be registering the hidden type. This is not supported right now. You can try moving the opaque type and the item that actually registers a hidden type into a new submodule
110+
--> $DIR/auto-trait-leak.rs:11:4
111+
|
112+
LL | fn cycle1() -> impl Clone {
113+
| ^^^^^^
114+
note: required by a bound in `send`
115+
--> $DIR/auto-trait-leak.rs:4:12
116+
|
117+
LL | fn send<T: Send>(_: T) {}
118+
| ^^^^ required by this bound in `send`
119+
120+
error: aborting due to 4 previous errors
38121

39122
For more information about this error, try `rustc --explain E0391`.

‎tests/ui/impl-trait/issue-103181-2.rs

+2
Original file line numberDiff line numberDiff line change
@@ -24,6 +24,8 @@ where
2424
B: Send, // <- a second bound
2525
{
2626
normalize(broken_fut(), ());
27+
//~^ ERROR: cannot check whether the hidden type of opaque type satisfies auto traits
28+
//~| ERROR: cannot check whether the hidden type of opaque type satisfies auto traits
2729
}
2830

2931
fn main() {}

‎tests/ui/impl-trait/issue-103181-2.stderr

+56-1
Original file line numberDiff line numberDiff line change
@@ -4,6 +4,61 @@ error[E0425]: cannot find value `ident_error` in this scope
44
LL | ident_error;
55
| ^^^^^^^^^^^ not found in this scope
66

7-
error: aborting due to previous error
7+
error: cannot check whether the hidden type of opaque type satisfies auto traits
8+
--> $DIR/issue-103181-2.rs:26:15
9+
|
10+
LL | normalize(broken_fut(), ());
11+
| --------- ^^^^^^^^^^^^
12+
| |
13+
| required by a bound introduced by this call
14+
|
15+
note: opaque type is declared here
16+
--> $DIR/issue-103181-2.rs:11:23
17+
|
18+
LL | async fn broken_fut() {
19+
| ^
20+
note: this item depends on auto traits of the hidden type, but may also be registering the hidden type. This is not supported right now. You can try moving the opaque type and the item that actually registers a hidden type into a new submodule
21+
--> $DIR/issue-103181-2.rs:20:10
22+
|
23+
LL | async fn iceice<A, B>()
24+
| ^^^^^^
25+
note: required for `impl Future<Output = ()>` to implement `SendFuture`
26+
--> $DIR/issue-103181-2.rs:7:17
27+
|
28+
LL | impl<Fut: Send> SendFuture for Fut {
29+
| ---- ^^^^^^^^^^ ^^^
30+
| |
31+
| unsatisfied trait bound introduced here
32+
note: required by a bound in `normalize`
33+
--> $DIR/issue-103181-2.rs:18:19
34+
|
35+
LL | fn normalize<Fut: SendFuture>(_: Fut, _: Fut::Output) {}
36+
| ^^^^^^^^^^ required by this bound in `normalize`
37+
38+
error: cannot check whether the hidden type of opaque type satisfies auto traits
39+
--> $DIR/issue-103181-2.rs:26:5
40+
|
41+
LL | normalize(broken_fut(), ());
42+
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^
43+
|
44+
note: opaque type is declared here
45+
--> $DIR/issue-103181-2.rs:11:23
46+
|
47+
LL | async fn broken_fut() {
48+
| ^
49+
note: this item depends on auto traits of the hidden type, but may also be registering the hidden type. This is not supported right now. You can try moving the opaque type and the item that actually registers a hidden type into a new submodule
50+
--> $DIR/issue-103181-2.rs:20:10
51+
|
52+
LL | async fn iceice<A, B>()
53+
| ^^^^^^
54+
note: required for `impl Future<Output = ()>` to implement `SendFuture`
55+
--> $DIR/issue-103181-2.rs:7:17
56+
|
57+
LL | impl<Fut: Send> SendFuture for Fut {
58+
| ---- ^^^^^^^^^^ ^^^
59+
| |
60+
| unsatisfied trait bound introduced here
61+
62+
error: aborting due to 3 previous errors
863

964
For more information about this error, try `rustc --explain E0425`.

‎tests/ui/type-alias-impl-trait/auto-trait-leakage3.rs

+2
Original file line numberDiff line numberDiff line change
@@ -6,13 +6,15 @@
66
mod m {
77
pub type Foo = impl std::fmt::Debug;
88
//~^ ERROR: cycle detected when computing type of `m::Foo::{opaque#0}` [E0391]
9+
//~| ERROR: cycle detected when computing type of `m::Foo::{opaque#0}` [E0391]
910

1011
pub fn foo() -> Foo {
1112
22_u32
1213
}
1314

1415
pub fn bar() {
1516
is_send(foo());
17+
//~^ ERROR: cannot check whether the hidden type of `auto_trait_leakage3[211d]::m::Foo::{opaque#0}
1618
}
1719

1820
fn is_send<T: Send>(_: T) {}

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