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Do not use effective_visibilities query for Adt types of a local trait while proving a where-clause #145642

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Merged
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Aug 21, 2025
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Do not use effective_visibilities query for Adt types of a local trait while proving a where-clause #145642

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2 changes: 1 addition & 1 deletion compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs
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Expand Up @@ -2878,7 +2878,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
// we check if `TraitB` can be reachable from `S`
// to determine whether to note `TraitA` is sealed trait.
if let ty::Adt(adt, _) = ty.kind() {
let visibilities = tcx.effective_visibilities(());
let visibilities = &tcx.resolutions(()).effective_visibilities;
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okay 🤔 what does the effective_visibilities query actually do with the effective_visibilities computed by by nameres? I generally feel like it should have some more comments somewhere.

cc @petrochenkov maybe?

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@xizheyin xizheyin Aug 20, 2025 •
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I noticed that in versions prior to #143431, &tcx.resolutions(()).effective_visibilities was used in this way. As for what exactly it does, I'm not quite sure. At the time, I used this API as suggested.🤔

https://github.com/rust-lang/rust/pull/143431/files#diff-c712eee556d0df70dfc5c8c66c34fa13fc94a30853854f632f5dd84acfd9c973L2778

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okay 🤔 what does the effective_visibilities query actually do with the effective_visibilities computed by by nameres?

Actually calculates them.
Name resolutions can only fill the "directly public" and "exported" levels, based on modules, reexports and nominal visibility.
The query uses type information and calculates the remaining "reachable" levels too.

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Here we are only checking Level::Reexported so it's ok to use the incomplete effective visibilities from name resolver.

visibilities.effective_vis(local).is_none_or(|v| {
v.at_level(Level::Reexported)
.is_accessible_from(adt.did(), tcx)
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11 changes: 11 additions & 0 deletions tests/ui/trait-bounds/trait-bound-adt-issue-145611.rs
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@@ -0,0 +1,11 @@
// This test is for regression of issue #145611
// There should not be cycle error in effective_visibilities query.

trait LocalTrait {}
struct SomeType;
fn impls_trait<T: LocalTrait>() {}
fn foo() -> impl Sized {
impls_trait::<SomeType>(); //~ ERROR the trait bound `SomeType: LocalTrait` is not satisfied [E0277]
}

fn main() {}
20 changes: 20 additions & 0 deletions tests/ui/trait-bounds/trait-bound-adt-issue-145611.stderr
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@@ -0,0 +1,20 @@
error[E0277]: the trait bound `SomeType: LocalTrait` is not satisfied
--> $DIR/trait-bound-adt-issue-145611.rs:8:19
|
LL | impls_trait::<SomeType>();
| ^^^^^^^^ the trait `LocalTrait` is not implemented for `SomeType`
|
help: this trait has no implementations, consider adding one
--> $DIR/trait-bound-adt-issue-145611.rs:4:1
|
LL | trait LocalTrait {}
| ^^^^^^^^^^^^^^^^
note: required by a bound in `impls_trait`
--> $DIR/trait-bound-adt-issue-145611.rs:6:19
|
LL | fn impls_trait<T: LocalTrait>() {}
| ^^^^^^^^^^ required by this bound in `impls_trait`

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0277`.
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