#![feature(trait_alias)]
trait Tree {
 type Fruit;
}
trait Grow1<T: Tree> {
 fn grow(x: T);
}
trait Grow2<T: Tree> = Grow1<T>;
struct AppleTree;
struct Apple;
impl Tree for AppleTree {
 type Fruit = Apple;
}
type GrowAppleTree1 = dyn Grow1<AppleTree>;
// semantically identical to the above line, but doesn't compile
type GrowAppleTree2 = dyn Grow2<AppleTree>; // (*)
fn main() {}

error[E0191]: the value of the associated type `Fruit` in `Tree` must be specified
 --> ..\..\rust\trait_alias_bug.rs:15:27
 |
3 | type Fruit;
 | ---------- `Fruit` defined here
...
15 | type GrowAppleTree2 = dyn Grow2<AppleTree>;
 | ^^^^^^^^^^^^^^^^ help: specify the associated type: `Grow2<AppleTree, Fruit = Type>`
error: aborting due to 1 previous error
For more information about this error, try `rustc --explain E0191`.

rustc 1.78.0-nightly (b6d2d841b 2024年03月05日)