Extended elaboration for trait aliases to include arbitrary bounds.

src/test/ui/traits/trait-alias-fail1.rs

@@ -8,13 +8,14 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// gate-test-trait_alias
+#![feature(trait_alias)]
 
 trait CloneDefault<T> = Default where T: Clone;
 trait BoundedAlias<T: Clone = ()> = Default;
 
-trait A<T: Send> {}
-trait B<T> = A<T>; // FIXME: parameter T should need a bound here, or semantics should be changed
+trait Foo {}
+trait A<T: Foo> {}
+trait B<T> = A<T>; // T cannot be unbounded
 
 impl CloneDefault for () {}
 

src/test/ui/traits/trait-alias-fail1.stderr

@@ -35,7 +35,7 @@ LL | trait BoundedAlias<T: Clone = ()> = Default;
 error[E0658]: trait aliases are experimental (see issue #41517)
   --> $DIR/trait-alias-fail1.rs:17:1
    |
-LL | trait B<T> = A<T>; // FIXME: this should not work... or should it?
+LL | trait B<T> = A<T>; // FIXME: parameter T should need a bound here, or semantics should be changed
    | ^^^^^^^^^^^^^^^^^^
    |
    = help: add #![feature(trait_alias)] to the crate attributes to enable

src/test/ui/traits/trait-alias-fail2.rs

@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// gate-test-trait_alias
+#![feature(trait_alias)]
 
 trait EqAlias = Eq;
 trait IteratorAlias = Iterator;