Add a regression test for issue-65384

Author: JohnTitor

src/test/ui/type-alias-impl-trait/issue-65384.rs

@@ -0,0 +1,16 @@
+#![feature(min_type_alias_impl_trait)]
+#![feature(type_alias_impl_trait)]
+#![allow(incomplete_features)]
+
+trait MyTrait {}
+
+impl MyTrait for () {}
+
+type Bar = impl MyTrait;
+
+impl MyTrait for Bar {}
+//~^ ERROR: cannot implement trait on type alias impl trait
+
+fn bazr() -> Bar { }
+
+fn main() {}

src/test/ui/type-alias-impl-trait/issue-65384.stderr

@@ -0,0 +1,14 @@
+error: cannot implement trait on type alias impl trait
+  --> $DIR/issue-65384.rs:11:1
+   |
+LL | impl MyTrait for Bar {}
+   | ^^^^^^^^^^^^^^^^^^^^
+   |
+note: type alias impl trait defined here
+  --> $DIR/issue-65384.rs:9:12
+   |
+LL | type Bar = impl MyTrait;
+   |            ^^^^^^^^^^^^
+
+error: aborting due to previous error
+