1 files changed, 24 insertions, 0 deletions
diff --git a/tests/ui/type-alias-impl-trait/unnameable_type.rs b/tests/ui/type-alias-impl-trait/unnameable_type.rs
new file mode 100644
index 000000000..1739ab006
--- /dev/null
+++ b/tests/ui/type-alias-impl-trait/unnameable_type.rs
@@ -0,0 +1,24 @@
+#![feature(type_alias_impl_trait)]
+
+// This test ensures that unnameable types stay unnameable
+// https://github.com/rust-lang/rust/issues/63063#issuecomment-1360053614
+
+// library
+mod private {
+    pub struct Private;
+    pub trait Trait {
+        fn dont_define_this(_private: Private) {}
+    }
+}
+
+use private::Trait;
+
+// downstream
+type MyPrivate = impl Sized;
+//~^ ERROR: unconstrained opaque type
+impl Trait for u32 {
+    fn dont_define_this(_private: MyPrivate) {}
+    //~^ ERROR: incompatible type for trait
+}
+
+fn main() {}