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Do not assemble candidates for auto traits of opaque types in their defining scope
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9 files changed

+76
-11
lines changed

9 files changed

+76
-11
lines changed

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

Lines changed: 6 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -777,7 +777,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
777777
);
778778
}
779779

780-
ty::Alias(ty::Opaque, _) => {
780+
ty::Alias(ty::Opaque, alias) => {
781781
if candidates.vec.iter().any(|c| matches!(c, ProjectionCandidate(_))) {
782782
// We do not generate an auto impl candidate for `impl Trait`s which already
783783
// reference our auto trait.
@@ -792,6 +792,11 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
792792
// We do not emit auto trait candidates for opaque types in coherence.
793793
// Doing so can result in weird dependency cycles.
794794
candidates.ambiguous = true;
795+
} else if self.infcx.can_define_opaque_ty(alias.def_id) {
796+
// We do not emit auto trait candidates for opaque types in their defining scope, as
797+
// we need to know the hidden type first, which we can't reliably know within the defining
798+
// scope.
799+
candidates.ambiguous = true;
795800
} else {
796801
candidates.vec.push(AutoImplCandidate)
797802
}

‎tests/ui/impl-trait/auto-trait-selection-freeze.next.stderr‎

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -1,5 +1,5 @@
11
error[E0283]: type annotations needed
2-
--> $DIR/auto-trait-selection-freeze.rs:20:16
2+
--> $DIR/auto-trait-selection-freeze.rs:19:16
33
|
44
LL | if false { is_trait(foo()) } else { Default::default() }
55
| ^^^^^^^^ ----- type must be known at this point
@@ -8,7 +8,7 @@ LL | if false { is_trait(foo()) } else { Default::default() }
88
|
99
= note: cannot satisfy `_: Trait<_>`
1010
note: required by a bound in `is_trait`
11-
--> $DIR/auto-trait-selection-freeze.rs:12:16
11+
--> $DIR/auto-trait-selection-freeze.rs:11:16
1212
|
1313
LL | fn is_trait<T: Trait<U>, U: Default>(_: T) -> U {
1414
| ^^^^^^^^ required by this bound in `is_trait`

‎tests/ui/impl-trait/auto-trait-selection-freeze.old.stderr‎

Lines changed: 26 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,26 @@
1+
error[E0283]: type annotations needed
2+
--> $DIR/auto-trait-selection-freeze.rs:19:16
3+
|
4+
LL | if false { is_trait(foo()) } else { Default::default() }
5+
| ^^^^^^^^ cannot infer type of the type parameter `U` declared on the function `is_trait`
6+
|
7+
note: multiple `impl`s satisfying `impl Sized: Trait<_>` found
8+
--> $DIR/auto-trait-selection-freeze.rs:16:1
9+
|
10+
LL | impl<T: Freeze> Trait<u32> for T {}
11+
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
12+
LL | impl<T> Trait<i32> for T {}
13+
| ^^^^^^^^^^^^^^^^^^^^^^^^
14+
note: required by a bound in `is_trait`
15+
--> $DIR/auto-trait-selection-freeze.rs:11:16
16+
|
17+
LL | fn is_trait<T: Trait<U>, U: Default>(_: T) -> U {
18+
| ^^^^^^^^ required by this bound in `is_trait`
19+
help: consider specifying the generic arguments
20+
|
21+
LL | if false { is_trait::<_, U>(foo()) } else { Default::default() }
22+
| ++++++++
23+
24+
error: aborting due to 1 previous error
25+
26+
For more information about this error, try `rustc --explain E0283`.

‎tests/ui/impl-trait/auto-trait-selection-freeze.rs‎

Lines changed: 1 addition & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -3,7 +3,6 @@
33
44
//@ revisions: next old
55
//@[next] compile-flags: -Znext-solver
6-
//@[old]check-pass
76

87
#![feature(freeze)]
98

@@ -18,7 +17,7 @@ impl<T: Freeze> Trait<u32> for T {}
1817
impl<T> Trait<i32> for T {}
1918
fn foo() -> impl Sized {
2019
if false { is_trait(foo()) } else { Default::default() }
21-
//[next]~^ ERROR: type annotations needed
20+
//~^ ERROR: type annotations needed
2221
}
2322

2423
fn main() {}

‎tests/ui/impl-trait/auto-trait-selection.next.stderr‎

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -1,5 +1,5 @@
11
error[E0283]: type annotations needed
2-
--> $DIR/auto-trait-selection.rs:16:16
2+
--> $DIR/auto-trait-selection.rs:15:16
33
|
44
LL | if false { is_trait(foo()) } else { Default::default() }
55
| ^^^^^^^^ ----- type must be known at this point
@@ -8,7 +8,7 @@ LL | if false { is_trait(foo()) } else { Default::default() }
88
|
99
= note: cannot satisfy `_: Trait<_>`
1010
note: required by a bound in `is_trait`
11-
--> $DIR/auto-trait-selection.rs:8:16
11+
--> $DIR/auto-trait-selection.rs:7:16
1212
|
1313
LL | fn is_trait<T: Trait<U>, U: Default>(_: T) -> U {
1414
| ^^^^^^^^ required by this bound in `is_trait`

‎tests/ui/impl-trait/auto-trait-selection.old.stderr‎

Lines changed: 26 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,26 @@
1+
error[E0283]: type annotations needed
2+
--> $DIR/auto-trait-selection.rs:15:16
3+
|
4+
LL | if false { is_trait(foo()) } else { Default::default() }
5+
| ^^^^^^^^ cannot infer type of the type parameter `U` declared on the function `is_trait`
6+
|
7+
note: multiple `impl`s satisfying `impl Sized: Trait<_>` found
8+
--> $DIR/auto-trait-selection.rs:12:1
9+
|
10+
LL | impl<T: Send> Trait<u32> for T {}
11+
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
12+
LL | impl<T> Trait<i32> for T {}
13+
| ^^^^^^^^^^^^^^^^^^^^^^^^
14+
note: required by a bound in `is_trait`
15+
--> $DIR/auto-trait-selection.rs:7:16
16+
|
17+
LL | fn is_trait<T: Trait<U>, U: Default>(_: T) -> U {
18+
| ^^^^^^^^ required by this bound in `is_trait`
19+
help: consider specifying the generic arguments
20+
|
21+
LL | if false { is_trait::<_, U>(foo()) } else { Default::default() }
22+
| ++++++++
23+
24+
error: aborting due to 1 previous error
25+
26+
For more information about this error, try `rustc --explain E0283`.

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

Lines changed: 1 addition & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -3,7 +3,6 @@
33
44
//@ revisions: next old
55
//@[next] compile-flags: -Znext-solver
6-
//@[old]check-pass
76

87
fn is_trait<T: Trait<U>, U: Default>(_: T) -> U {
98
Default::default()
@@ -14,7 +13,7 @@ impl<T: Send> Trait<u32> for T {}
1413
impl<T> Trait<i32> for T {}
1514
fn foo() -> impl Sized {
1615
if false { is_trait(foo()) } else { Default::default() }
17-
//[next]~^ ERROR: type annotations needed
16+
//~^ ERROR: type annotations needed
1817
}
1918

2019
fn main() {}

‎tests/ui/type-alias-impl-trait/in-where-clause.rs‎

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -8,6 +8,7 @@ type Bar = impl Sized;
88
fn foo() -> Bar
99
where
1010
Bar: Send,
11+
//~^ ERROR: type annotations needed
1112
{
1213
[0; 1 + 2]
1314
}

‎tests/ui/type-alias-impl-trait/in-where-clause.stderr‎

Lines changed: 11 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -25,6 +25,15 @@ LL | type Bar = impl Sized;
2525
| ^^^^^^^^^^
2626
= note: see https://rustc-dev-guide.rust-lang.org/overview.html#queries and https://rustc-dev-guide.rust-lang.org/query.html for more information
2727

28-
error: aborting due to 1 previous error
28+
error[E0283]: type annotations needed: cannot satisfy `Bar: Send`
29+
--> $DIR/in-where-clause.rs:10:10
30+
|
31+
LL | Bar: Send,
32+
| ^^^^
33+
|
34+
= note: cannot satisfy `Bar: Send`
35+
36+
error: aborting due to 2 previous errors
2937

30-
For more information about this error, try `rustc --explain E0391`.
38+
Some errors have detailed explanations: E0283, E0391.
39+
For more information about an error, try `rustc --explain E0283`.

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