Auto merge of rust-lang#121200 - estebank:inferred_outlives_of-impl, r=<try>

Deduplicate object safety errors on `impl dyn Trait { .. }`

`impl dyn Trait {}` has an implicit `dyn Trait: 'static` bound. We add it in `inferred_outlives_of` for more context in errors. With this we point at `impl dyn Trait` and not to it's associated functions, deduplicating errors to a single one per `impl dyn Trait` instead of one for it plus one for each associated function.

CC rust-lang#83246, as this is necessary but not sufficient to help with the lack of tracking of `'static` obligations.

Author: bors

compiler/rustc_hir_analysis/src/outlives/mod.rs

@@ -1,3 +1,4 @@
+use rustc_hir as hir;
 use rustc_hir::def::DefKind;
 use rustc_hir::def_id::LocalDefId;
 use rustc_middle::query::Providers;
@@ -46,6 +47,24 @@ fn inferred_outlives_of(tcx: TyCtxt<'_>, item_def_id: LocalDefId) -> &[(ty::Clau
                 &[]
             }
         }
+        DefKind::Impl { of_trait: false }
+            if let hir::ItemKind::Impl(item) = tcx.hir().expect_item(item_def_id).kind
+                && let hir::Impl { self_ty, .. } = &item
+                && let hir::TyKind::TraitObject(
+                    _,
+                    hir::Lifetime { res: hir::LifetimeName::ImplicitObjectLifetimeDefault, .. },
+                    _,
+                ) = self_ty.kind =>
+        {
+            // `impl dyn Trait {}` has an implicit `dyn Trait: 'static` bound. We add it here for
+            // more context in errors. With this we point at `impl dyn Trait` and not to it's
+            // associated functions, deduplicating errors to a single one per `impl dyn Trait` instead
+            // of one for it plus one for each associated function.
+            let ty = tcx.type_of(item_def_id).instantiate_identity();
+            let clause_kind =
+                ty::ClauseKind::TypeOutlives(ty::OutlivesPredicate(ty, tcx.lifetimes.re_static));
+            &*tcx.arena.alloc_from_iter([(clause_kind.to_predicate(tcx), self_ty.span)])
+        }
         _ => &[],
     }
 }

tests/ui/associated-consts/associated-const-in-trait.rs

@@ -6,6 +6,7 @@ trait Trait {
 
 impl dyn Trait {
     //~^ ERROR the trait `Trait` cannot be made into an object [E0038]
+    //~| ERROR the trait `Trait` cannot be made into an object [E0038]
     const fn n() -> usize { Self::N }
     //~^ ERROR the trait `Trait` cannot be made into an object [E0038]
 }

tests/ui/associated-consts/associated-const-in-trait.stderr

@@ -14,7 +14,23 @@ LL |     const N: usize;
    = help: consider moving `N` to another trait
 
 error[E0038]: the trait `Trait` cannot be made into an object
-  --> $DIR/associated-const-in-trait.rs:9:29
+  --> $DIR/associated-const-in-trait.rs:7:6
+   |
+LL | impl dyn Trait {
+   |      ^^^^^^^^^ `Trait` 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/associated-const-in-trait.rs:4:11
+   |
+LL | trait Trait {
+   |       ----- this trait cannot be made into an object...
+LL |     const N: usize;
+   |           ^ ...because it contains this associated `const`
+   = help: consider moving `N` to another trait
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
+
+error[E0038]: the trait `Trait` cannot be made into an object
+  --> $DIR/associated-const-in-trait.rs:10:29
    |
 LL |     const fn n() -> usize { Self::N }
    |                             ^^^^ `Trait` cannot be made into an object
@@ -28,6 +44,6 @@ LL |     const N: usize;
    |           ^ ...because it contains this associated `const`
    = help: consider moving `N` to another trait
 
-error: aborting due to 2 previous errors
+error: aborting due to 3 previous errors
 
 For more information about this error, try `rustc --explain E0038`.

tests/ui/impl-trait/in-trait/cycle-effective-visibilities-during-object-safety.rs

@@ -15,8 +15,8 @@ impl MyTrait for Outer {
 
 impl dyn MyTrait {
     //~^ ERROR the trait `MyTrait` cannot be made into an object
+    //~| 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

tests/ui/impl-trait/in-trait/cycle-effective-visibilities-during-object-safety.stderr

@@ -49,10 +49,10 @@ LL |     fn foo(&self) -> impl Marker;
    = 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
+  --> $DIR/cycle-effective-visibilities-during-object-safety.rs:16:6
    |
-LL |     fn other(&self) -> impl Marker {
-   |               ^^^^ `MyTrait` cannot be made into an object
+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
@@ -63,6 +63,7 @@ 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
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 5 previous errors