Change:
No response No response This code is originally extracted from a reduction of a problem found hit on a . I reduced the code down to something that, confusingly, provides an incorrect diagnostics message. Originally, the dynamic dispatch were , I just substituted them. The nightly toolchain as of today behaves the same. As a note, the correct output is provided if the statement is commented out, which is why I think this is related to , but maybe not the same.
This is a duplicate of , so I'll close this in favor of that. I do agree that it's a diagnostic issue, so I will fix it.

Discussion:
}; let externally_visible = if !impls.is_empty() && let Some(def_id) = trait_def_id.as_local() <del> && tcx.effective_visibilities(()).is_exported(def_id) </del> <ins> // We may be executing this during typeck, which would result in cycle // if we used effective_visibilities query, which looks into opaque types // (and therefore calls typeck). && tcx.resolutions(()).effective_visibilities.is_exported(def_id) </ins> { true } else {

<ins> trait Marker {} impl Marker for u32 {} trait MyTrait { fn foo(&self) -> impl Marker; } struct Outer; impl MyTrait for Outer { fn foo(&self) -> impl Marker { 42 } } impl dyn MyTrait { //~^ ERROR the trait `MyTrait` cannot be made into an object fn other(&self) -> impl Marker { //~^ ERROR the trait `MyTrait` cannot be made into an object MyTrait::foo(&self) //~^ ERROR the trait bound `&dyn MyTrait: MyTrait` is not satisfied //~| ERROR the trait bound `&dyn MyTrait: MyTrait` is not satisfied //~| ERROR the trait bound `&dyn MyTrait: MyTrait` is not satisfied //~| ERROR the trait `MyTrait` cannot be made into an object } } fn main() {} </ins>

<ins> error[E0277]: the trait bound `&dyn MyTrait: MyTrait` is not satisfied --> $DIR/cycle-effective-visibilities-during-object-safety.rs:20:22 | LL |         MyTrait::foo(&self) |         ------------ ^^^^^ the trait `MyTrait` is not implemented for `&dyn MyTrait` |         | |         required by a bound introduced by this call | = help: the trait `MyTrait` is implemented for `Outer` error[E0038]: the trait `MyTrait` cannot be made into an object --> $DIR/cycle-effective-visibilities-during-object-safety.rs:20:9 | LL |         MyTrait::foo(&self) |         ^^^^^^^^^^^^ `MyTrait` cannot be made into an object | note: for a trait to be "object safe" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety> --> $DIR/cycle-effective-visibilities-during-object-safety.rs:5:22 | LL | trait MyTrait { |       ------- this trait cannot be made into an object... LL |     fn foo(&self) -> impl Marker; |                      ^^^^^^^^^^^ ...because method `foo` references an `impl Trait` type in its return type = help: consider moving `foo` to another trait = help: only type `Outer` implements the trait, consider using it directly instead error[E0277]: the trait bound `&dyn MyTrait: MyTrait` is not satisfied --> $DIR/cycle-effective-visibilities-during-object-safety.rs:20:9 | LL |         MyTrait::foo(&self) |         ^^^^^^^^^^^^^^^^^^^ the trait `MyTrait` is not implemented for `&dyn MyTrait` | = help: the trait `MyTrait` is implemented for `Outer` error[E0277]: the trait bound `&dyn MyTrait: MyTrait` is not satisfied --> $DIR/cycle-effective-visibilities-during-object-safety.rs:20:9 | LL |         MyTrait::foo(&self) |         ^^^^^^^^^^^^ the trait `MyTrait` is not implemented for `&dyn MyTrait` | = help: the trait `MyTrait` is implemented for `Outer` error[E0038]: the trait `MyTrait` cannot be made into an object --> $DIR/cycle-effective-visibilities-during-object-safety.rs:16:6 | LL | impl dyn MyTrait { |      ^^^^^^^^^^^ `MyTrait` cannot be made into an object | note: for a trait to be "object safe" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety> --> $DIR/cycle-effective-visibilities-during-object-safety.rs:5:22 | LL | trait MyTrait { |       ------- this trait cannot be made into an object... LL |     fn foo(&self) -> impl Marker; |                      ^^^^^^^^^^^ ...because method `foo` references an `impl Trait` type in its return type = help: consider moving `foo` to another trait = help: only type `Outer` implements the trait, consider using it directly instead error[E0038]: the trait `MyTrait` cannot be made into an object --> $DIR/cycle-effective-visibilities-during-object-safety.rs:18:15 | LL |     fn other(&self) -> impl Marker { |               ^^^^ `MyTrait` cannot be made into an object | note: for a trait to be "object safe" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety> --> $DIR/cycle-effective-visibilities-during-object-safety.rs:5:22 | LL | trait MyTrait { |       ------- this trait cannot be made into an object... LL |     fn foo(&self) -> impl Marker; |                      ^^^^^^^^^^^ ...because method `foo` references an `impl Trait` type in its return type = help: consider moving `foo` to another trait = help: only type `Outer` implements the trait, consider using it directly instead error: aborting due to 6 previous errors Some errors have detailed explanations: E0038, E0277. For more information about an error, try `rustc --explain E0038`. </ins>