rust-lang · bors · May 27, 2025 · May 26, 2025
diff --git a/compiler/rustc_hir_analysis/src/collect.rs b/compiler/rustc_hir_analysis/src/collect.rs
@@ -31,7 +31,7 @@ use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_hir::intravisit::{self, InferKind, Visitor, VisitorExt, walk_generics};
 use rustc_hir::{self as hir, GenericParamKind, HirId, Node, PreciseCapturingArgKind};
 use rustc_infer::infer::{InferCtxt, TyCtxtInferExt};
-use rustc_infer::traits::ObligationCause;
+use rustc_infer::traits::{DynCompatibilityViolation, ObligationCause};
 use rustc_middle::hir::nested_filter;
 use rustc_middle::query::Providers;
 use rustc_middle::ty::util::{Discr, IntTypeExt};
@@ -40,7 +40,7 @@ use rustc_middle::{bug, span_bug};
 use rustc_span::{DUMMY_SP, Ident, Span, Symbol, kw, sym};
 use rustc_trait_selection::error_reporting::traits::suggestions::NextTypeParamName;
 use rustc_trait_selection::infer::InferCtxtExt;
-use rustc_trait_selection::traits::ObligationCtxt;
+use rustc_trait_selection::traits::{ObligationCtxt, hir_ty_lowering_dyn_compatibility_violations};
 use tracing::{debug, instrument};
 
 use crate::errors;
@@ -625,6 +625,10 @@ impl<'tcx> HirTyLowerer<'tcx> for ItemCtxt<'tcx> {
 
         (input_tys, output_ty)
     }
+
+    fn dyn_compatibility_violations(&self, trait_def_id: DefId) -> Vec<DynCompatibilityViolation> {
+        hir_ty_lowering_dyn_compatibility_violations(self.tcx, trait_def_id)
+    }
 }
 
 /// Synthesize a new lifetime name that doesn't clash with any of the lifetimes already present.

diff --git a/compiler/rustc_hir_analysis/src/hir_ty_lowering/dyn_compatibility.rs b/compiler/rustc_hir_analysis/src/hir_ty_lowering/dyn_compatibility.rs
@@ -11,7 +11,7 @@ use rustc_middle::ty::{
 };
 use rustc_span::{ErrorGuaranteed, Span};
 use rustc_trait_selection::error_reporting::traits::report_dyn_incompatibility;
-use rustc_trait_selection::traits::{self, hir_ty_lowering_dyn_compatibility_violations};
+use rustc_trait_selection::traits;
 use smallvec::{SmallVec, smallvec};
 use tracing::{debug, instrument};
 
@@ -97,8 +97,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         // to avoid ICEs.
         for (clause, span) in user_written_bounds {
             if let Some(trait_pred) = clause.as_trait_clause() {
-                let violations =
-                    hir_ty_lowering_dyn_compatibility_violations(tcx, trait_pred.def_id());
+                let violations = self.dyn_compatibility_violations(trait_pred.def_id());
                 if !violations.is_empty() {
                     let reported = report_dyn_incompatibility(
                         tcx,

diff --git a/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs b/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs
@@ -33,7 +33,7 @@ use rustc_hir::def::{CtorKind, CtorOf, DefKind, Res};
 use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_hir::{self as hir, AnonConst, GenericArg, GenericArgs, HirId};
 use rustc_infer::infer::{InferCtxt, TyCtxtInferExt};
-use rustc_infer::traits::ObligationCause;
+use rustc_infer::traits::{DynCompatibilityViolation, ObligationCause};
 use rustc_middle::middle::stability::AllowUnstable;
 use rustc_middle::mir::interpret::LitToConstInput;
 use rustc_middle::ty::print::PrintPolyTraitRefExt as _;
@@ -200,6 +200,10 @@ pub trait HirTyLowerer<'tcx> {
     {
         self
     }
+
+    /// Performs minimalistic dyn compat checks outside of bodies, but full within bodies.
+    /// Outside of bodies we could end up in cycles, so we delay most checks to later phases.
+    fn dyn_compatibility_violations(&self, trait_def_id: DefId) -> Vec<DynCompatibilityViolation>;
 }
 
 /// The "qualified self" of an associated item path.

diff --git a/compiler/rustc_hir_typeck/src/fn_ctxt/mod.rs b/compiler/rustc_hir_typeck/src/fn_ctxt/mod.rs
@@ -14,7 +14,7 @@ use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_hir::{self as hir, HirId, ItemLocalMap};
 use rustc_hir_analysis::hir_ty_lowering::{HirTyLowerer, RegionInferReason};
 use rustc_infer::infer;
-use rustc_infer::traits::Obligation;
+use rustc_infer::traits::{DynCompatibilityViolation, Obligation};
 use rustc_middle::ty::{self, Const, Ty, TyCtxt, TypeVisitableExt};
 use rustc_session::Session;
 use rustc_span::{self, DUMMY_SP, ErrorGuaranteed, Ident, Span, sym};
@@ -388,6 +388,10 @@ impl<'tcx> HirTyLowerer<'tcx> for FnCtxt<'_, 'tcx> {
         };
         (input_tys, output_ty)
     }
+
+    fn dyn_compatibility_violations(&self, trait_def_id: DefId) -> Vec<DynCompatibilityViolation> {
+        self.tcx.dyn_compatibility_violations(trait_def_id).to_vec()
+    }
 }
 
 /// The `ty` representation of a user-provided type. Depending on the use-site

diff --git a/tests/ui/async-await/dyn/mut-is-pointer-like.stderr b/tests/ui/async-await/dyn/mut-is-pointer-like.stderr
@@ -8,10 +8,10 @@ LL | #![feature(async_fn_in_dyn_trait)]
    = note: `#[warn(incomplete_features)]` on by default
 
 error[E0038]: the trait `AsyncTrait` is not dyn compatible
-  --> $DIR/mut-is-pointer-like.rs:35:16
+  --> $DIR/mut-is-pointer-like.rs:35:29
    |
 LL |         let x: Pin<&mut dyn AsyncTrait<Output = ()>> = f;
-   |                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `AsyncTrait` is not dyn compatible
+   |                             ^^^^^^^^^^^^^^^^^^^^^^^ `AsyncTrait` is not dyn compatible
    |
 note: for a trait to be dyn compatible it needs to allow building a vtable
       for more information, visit <https://doc.rust-lang.org/reference/items/traits.html#dyn-compatibility>

diff --git a/tests/ui/async-await/dyn/works.stderr b/tests/ui/async-await/dyn/works.stderr
@@ -8,10 +8,10 @@ LL | #![feature(async_fn_in_dyn_trait)]
    = note: `#[warn(incomplete_features)]` on by default
 
 error[E0038]: the trait `AsyncTrait` is not dyn compatible
-  --> $DIR/works.rs:27:16
+  --> $DIR/works.rs:27:21
    |
 LL |         let x: &dyn AsyncTrait = &"hello, world!";
-   |                ^^^^^^^^^^^^^^^ `AsyncTrait` is not dyn compatible
+   |                     ^^^^^^^^^^ `AsyncTrait` is not dyn compatible
    |
 note: for a trait to be dyn compatible it needs to allow building a vtable
       for more information, visit <https://doc.rust-lang.org/reference/items/traits.html#dyn-compatibility>

diff --git a/tests/ui/async-await/dyn/wrong-size.stderr b/tests/ui/async-await/dyn/wrong-size.stderr
@@ -8,10 +8,10 @@ LL | #![feature(async_fn_in_dyn_trait)]
    = note: `#[warn(incomplete_features)]` on by default
 
 error[E0038]: the trait `AsyncTrait` is not dyn compatible
-  --> $DIR/wrong-size.rs:21:12
+  --> $DIR/wrong-size.rs:21:17
    |
 LL |     let x: &dyn AsyncTrait = &"hello, world!";
-   |            ^^^^^^^^^^^^^^^ `AsyncTrait` is not dyn compatible
+   |                 ^^^^^^^^^^ `AsyncTrait` is not dyn compatible
    |
 note: for a trait to be dyn compatible it needs to allow building a vtable
       for more information, visit <https://doc.rust-lang.org/reference/items/traits.html#dyn-compatibility>

diff --git a/tests/ui/async-await/in-trait/dyn-compatibility.stderr b/tests/ui/async-await/in-trait/dyn-compatibility.stderr
@@ -1,8 +1,8 @@
 error[E0038]: the trait `Foo` is not dyn compatible
-  --> $DIR/dyn-compatibility.rs:9:12
+  --> $DIR/dyn-compatibility.rs:9:17
    |
 LL |     let x: &dyn Foo = todo!();
-   |            ^^^^^^^^ `Foo` is not dyn compatible
+   |                 ^^^ `Foo` is not dyn compatible
    |
 note: for a trait to be dyn compatible it needs to allow building a vtable
       for more information, visit <https://doc.rust-lang.org/reference/items/traits.html#dyn-compatibility>

diff --git a/tests/ui/did_you_mean/trait-object-reference-without-parens-suggestion.rs b/tests/ui/did_you_mean/trait-object-reference-without-parens-suggestion.rs
@@ -4,4 +4,5 @@ fn main() {
     let _: &Copy + 'static; //~ ERROR expected a path
     //~^ ERROR is not dyn compatible
     let _: &'static Copy + 'static; //~ ERROR expected a path
+    //~^ ERROR is not dyn compatible
 }
diff --git a/tests/ui/did_you_mean/trait-object-reference-without-parens-suggestion.stderr b/tests/ui/did_you_mean/trait-object-reference-without-parens-suggestion.stderr
@@ -21,16 +21,26 @@ LL |     let _: &'static (Copy + 'static);
    |                     +              +
 
 error[E0038]: the trait `Copy` is not dyn compatible
-  --> $DIR/trait-object-reference-without-parens-suggestion.rs:4:12
+  --> $DIR/trait-object-reference-without-parens-suggestion.rs:4:13
    |
 LL |     let _: &Copy + 'static;
-   |            ^^^^^ `Copy` is not dyn compatible
+   |             ^^^^ `Copy` is not dyn compatible
+   |
+   = note: the trait is not dyn compatible because it requires `Self: Sized`
+   = note: for a trait to be dyn compatible it needs to allow building a vtable
+           for more information, visit <https://doc.rust-lang.org/reference/items/traits.html#dyn-compatibility>
+
+error[E0038]: the trait `Copy` is not dyn compatible
+  --> $DIR/trait-object-reference-without-parens-suggestion.rs:6:21
+   |
+LL |     let _: &'static Copy + 'static;
+   |                     ^^^^ `Copy` is not dyn compatible
    |
    = note: the trait is not dyn compatible because it requires `Self: Sized`
    = note: for a trait to be dyn compatible it needs to allow building a vtable
            for more information, visit <https://doc.rust-lang.org/reference/items/traits.html#dyn-compatibility>
 
-error: aborting due to 3 previous errors
+error: aborting due to 4 previous errors
 
 Some errors have detailed explanations: E0038, E0178.
 For more information about an error, try `rustc --explain E0038`.
diff --git a/tests/ui/dyn-compatibility/almost-supertrait-associated-type.stderr b/tests/ui/dyn-compatibility/almost-supertrait-associated-type.stderr
@@ -16,10 +16,10 @@ LL |     fn transmute(&self, t: T) -> <Self as Super<NotActuallySuper>>::Assoc;
    = help: consider moving `transmute` to another trait
 
 error[E0038]: the trait `Foo` is not dyn compatible
-  --> $DIR/almost-supertrait-associated-type.rs:7:27
+  --> $DIR/almost-supertrait-associated-type.rs:7:32
    |
 LL |     (&PhantomData::<T> as &dyn Foo<T, U>).transmute(t)
-   |                           ^^^^^^^^^^^^^^ `Foo` is not dyn compatible
+   |                                ^^^^^^^^^ `Foo` is not dyn compatible
    |
 note: for a trait to be dyn compatible it needs to allow building a vtable
       for more information, visit <https://doc.rust-lang.org/reference/items/traits.html#dyn-compatibility>

diff --git a/tests/ui/dyn-compatibility/generics.stderr b/tests/ui/dyn-compatibility/generics.stderr
@@ -31,10 +31,10 @@ LL |     fn bar<T>(&self, t: T);
    = help: consider moving `bar` to another trait
 
 error[E0038]: the trait `Bar` is not dyn compatible
-  --> $DIR/generics.rs:22:10
+  --> $DIR/generics.rs:22:15
    |
 LL |     t as &dyn Bar
-   |          ^^^^^^^^ `Bar` is not dyn compatible
+   |               ^^^ `Bar` is not dyn compatible
    |
 note: for a trait to be dyn compatible it needs to allow building a vtable
       for more information, visit <https://doc.rust-lang.org/reference/items/traits.html#dyn-compatibility>

diff --git a/tests/ui/dyn-compatibility/mention-correct-dyn-incompatible-trait.stderr b/tests/ui/dyn-compatibility/mention-correct-dyn-incompatible-trait.stderr
@@ -1,8 +1,8 @@
 error[E0038]: the trait `Bar` is not dyn compatible
-  --> $DIR/mention-correct-dyn-incompatible-trait.rs:19:15
+  --> $DIR/mention-correct-dyn-incompatible-trait.rs:19:24
    |
 LL |     let test: &mut dyn Bar = &mut thing;
-   |               ^^^^^^^^^^^^ `Bar` is not dyn compatible
+   |                        ^^^ `Bar` is not dyn compatible
    |
 note: for a trait to be dyn compatible it needs to allow building a vtable
       for more information, visit <https://doc.rust-lang.org/reference/items/traits.html#dyn-compatibility>

diff --git a/tests/ui/dyn-compatibility/no-static.stderr b/tests/ui/dyn-compatibility/no-static.stderr
@@ -23,10 +23,10 @@ LL |     fn foo() where Self: Sized {}
    |              +++++++++++++++++
 
 error[E0038]: the trait `Foo` is not dyn compatible
-  --> $DIR/no-static.rs:18:12
+  --> $DIR/no-static.rs:18:20
    |
 LL |     let b: Box<dyn Foo> = Box::new(Bar);
-   |            ^^^^^^^^^^^^ `Foo` is not dyn compatible
+   |                    ^^^ `Foo` is not dyn compatible
    |
 note: for a trait to be dyn compatible it needs to allow building a vtable
       for more information, visit <https://doc.rust-lang.org/reference/items/traits.html#dyn-compatibility>

diff --git a/tests/ui/feature-gates/feature-gate-dispatch-from-dyn-missing-impl.stderr b/tests/ui/feature-gates/feature-gate-dispatch-from-dyn-missing-impl.stderr
@@ -1,11 +1,11 @@
 error[E0038]: the trait `Trait` is not dyn compatible
-  --> $DIR/feature-gate-dispatch-from-dyn-missing-impl.rs:32:25
+  --> $DIR/feature-gate-dispatch-from-dyn-missing-impl.rs:32:33
    |
 LL |     fn ptr(self: Ptr<Self>);
    |                  --------- help: consider changing method `ptr`'s `self` parameter to be `&self`: `&Self`
 ...
 LL |     Ptr(Box::new(4)) as Ptr<dyn Trait>;
-   |                         ^^^^^^^^^^^^^^ `Trait` is not dyn compatible
+   |                                 ^^^^^ `Trait` is not dyn compatible
    |
 note: for a trait to be dyn compatible it needs to allow building a vtable
       for more information, visit <https://doc.rust-lang.org/reference/items/traits.html#dyn-compatibility>

diff --git a/tests/ui/generic-associated-types/issue-76535.stderr b/tests/ui/generic-associated-types/issue-76535.stderr
@@ -15,10 +15,10 @@ LL |     let sub: Box<dyn SuperTrait<SubType<'a> = SubStruct>> = Box::new(SuperS
    |                                        ++++
 
 error[E0038]: the trait `SuperTrait` is not dyn compatible
-  --> $DIR/issue-76535.rs:34:14
+  --> $DIR/issue-76535.rs:34:22
    |
 LL |     let sub: Box<dyn SuperTrait<SubType = SubStruct>> = Box::new(SuperStruct::new(0));
-   |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `SuperTrait` is not dyn compatible
+   |                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `SuperTrait` is not dyn compatible
    |
 note: for a trait to be dyn compatible it needs to allow building a vtable
       for more information, visit <https://doc.rust-lang.org/reference/items/traits.html#dyn-compatibility>

diff --git a/tests/ui/generic-associated-types/issue-78671.stderr b/tests/ui/generic-associated-types/issue-78671.stderr
@@ -15,10 +15,10 @@ LL |     Box::new(Family) as &dyn CollectionFamily<Member<T>=usize>
    |                                                     +++
 
 error[E0038]: the trait `CollectionFamily` is not dyn compatible
-  --> $DIR/issue-78671.rs:5:25
+  --> $DIR/issue-78671.rs:5:30
    |
 LL |     Box::new(Family) as &dyn CollectionFamily<Member=usize>
-   |                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `CollectionFamily` is not dyn compatible
+   |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `CollectionFamily` is not dyn compatible
    |
 note: for a trait to be dyn compatible it needs to allow building a vtable
       for more information, visit <https://doc.rust-lang.org/reference/items/traits.html#dyn-compatibility>

diff --git a/tests/ui/generic-associated-types/issue-79422.stderr b/tests/ui/generic-associated-types/issue-79422.stderr
@@ -15,10 +15,10 @@ LL |         as Box<dyn MapLike<u8, u8, VRefCont<'a> = dyn RefCont<'_, u8>>>;
    |                                            ++++
 
 error[E0038]: the trait `MapLike` is not dyn compatible
-  --> $DIR/issue-79422.rs:45:12
+  --> $DIR/issue-79422.rs:45:20
    |
 LL |         as Box<dyn MapLike<u8, u8, VRefCont = dyn RefCont<'_, u8>>>;
-   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `MapLike` is not dyn compatible
+   |                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `MapLike` is not dyn compatible
    |
 note: for a trait to be dyn compatible it needs to allow building a vtable
       for more information, visit <https://doc.rust-lang.org/reference/items/traits.html#dyn-compatibility>

diff --git a/tests/ui/higher-ranked/trait-bounds/span-bug-issue-121597.rs b/tests/ui/higher-ranked/trait-bounds/span-bug-issue-121597.rs
@@ -15,5 +15,4 @@ fn main() {
     //~^ ERROR the trait `Foo` is not dyn compatible
 
     needs_bar(x);
-    //~^ ERROR mismatched types
 }
diff --git a/tests/ui/higher-ranked/trait-bounds/span-bug-issue-121597.stderr b/tests/ui/higher-ranked/trait-bounds/span-bug-issue-121597.stderr
@@ -1,8 +1,8 @@
 error[E0038]: the trait `Foo` is not dyn compatible
-  --> $DIR/span-bug-issue-121597.rs:14:12
+  --> $DIR/span-bug-issue-121597.rs:14:17
    |
 LL |     let x: &dyn Foo = &();
-   |            ^^^^^^^^ `Foo` is not dyn compatible
+   |                 ^^^ `Foo` is not dyn compatible
    |
 note: for a trait to be dyn compatible it needs to allow building a vtable
       for more information, visit <https://doc.rust-lang.org/reference/items/traits.html#dyn-compatibility>
@@ -13,23 +13,6 @@ LL | trait Foo: for<T> Bar<T> {}
    |       |
    |       this trait is not dyn compatible...
 
-error[E0308]: mismatched types
-  --> $DIR/span-bug-issue-121597.rs:17:15
-   |
-LL |     needs_bar(x);
-   |     --------- ^ types differ in mutability
-   |     |
-   |     arguments to this function are incorrect
-   |
-   = note: expected raw pointer `*mut Type2`
-                found reference `&dyn Foo`
-note: function defined here
-  --> $DIR/span-bug-issue-121597.rs:11:4
-   |
-LL | fn needs_bar(_: *mut Type2) {}
-   |    ^^^^^^^^^ -------------
-
-error: aborting due to 2 previous errors
+error: aborting due to 1 previous error
 
-Some errors have detailed explanations: E0038, E0308.
-For more information about an error, try `rustc --explain E0038`.
+For more information about this error, try `rustc --explain E0038`.
diff --git a/tests/ui/impl-trait/dyn-incompatible-trait-in-return-position-dyn-trait.rs b/tests/ui/impl-trait/dyn-incompatible-trait-in-return-position-dyn-trait.rs
@@ -21,6 +21,8 @@ impl DynIncompatible for B {
 
 fn car() -> dyn DynIncompatible { //~ ERROR the trait `DynIncompatible` is not dyn compatible
 //~^ ERROR return type cannot be a trait object without pointer indirection
+//~| ERROR the trait `DynIncompatible` is not dyn compatible
+//~| ERROR the trait `DynIncompatible` is not dyn compatible
     if true {
         return A;
     }