diff --git a/compiler/rustc_hir_analysis/src/coherence/orphan.rs b/compiler/rustc_hir_analysis/src/coherence/orphan.rs
index cc5114dba5efe..c6d4aeefc80e5 100644
--- a/compiler/rustc_hir_analysis/src/coherence/orphan.rs
+++ b/compiler/rustc_hir_analysis/src/coherence/orphan.rs
@@ -184,11 +184,19 @@ fn emit_orphan_check_error<'tcx>(
ty::Adt(def, _) => tcx.mk_adt(*def, ty::List::empty()),
_ => ty,
};
- let this = "this".to_string();
- let (ty, postfix) = match &ty.kind() {
- ty::Slice(_) => (this, " because slices are always foreign"),
- ty::Array(..) => (this, " because arrays are always foreign"),
- ty::Tuple(..) => (this, " because tuples are always foreign"),
+ let msg = |ty: &str, postfix: &str| {
+ format!("{ty} is not defined in the current crate{postfix}")
+ };
+ let this = |name: &str| msg("this", &format!(" because {name} are always foreign"));
+ let msg = match &ty.kind() {
+ ty::Slice(_) => this("slices"),
+ ty::Array(..) => this("arrays"),
+ ty::Tuple(..) => this("tuples"),
+ ty::Alias(ty::Opaque, ..) => {
+ "type alias impl trait is treated as if it were foreign, \
+ because its hidden type could be from a foreign crate"
+ .to_string()
+ }
ty::RawPtr(ptr_ty) => {
emit_newtype_suggestion_for_raw_ptr(
full_impl_span,
@@ -198,12 +206,11 @@ fn emit_orphan_check_error<'tcx>(
&mut err,
);
- (format!("`{}`", ty), " because raw pointers are always foreign")
+ msg(&format!("`{ty}`"), " because raw pointers are always foreign")
}
- _ => (format!("`{}`", ty), ""),
+ _ => msg(&format!("`{ty}`"), ""),
};
- let msg = format!("{} is not defined in the current crate{}", ty, postfix);
if is_target_ty {
// Point at `D` in `impl for C in D`
err.span_label(self_ty_span, &msg);
diff --git a/src/test/ui/type-alias-impl-trait/coherence.stderr b/src/test/ui/type-alias-impl-trait/coherence.stderr
index c923eb08ab312..00b0dbbb583fd 100644
--- a/src/test/ui/type-alias-impl-trait/coherence.stderr
+++ b/src/test/ui/type-alias-impl-trait/coherence.stderr
@@ -4,7 +4,7 @@ error[E0117]: only traits defined in the current crate can be implemented for ar
LL | impl foreign_crate::ForeignTrait for AliasOfForeignType {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^---------------------
| | |
- | | `AliasOfForeignType` is not defined in the current crate
+ | | type alias impl trait is treated as if it were foreign, because its hidden type could be from a foreign crate
| impl doesn't use only types from inside the current crate
|
= note: define and implement a trait or new type instead