rustc: fix ICE when trait alias has bare Self

src/test/ui/issues/issue-59029-1.rs

@@ -0,0 +1,8 @@
+#![feature(trait_alias)]
+
+trait Svc<Req> { type Res; }
+
+trait MkSvc<Target, Req> = Svc<Target> where Self::Res: Svc<Req>;
+//~^ ERROR associated type `Res` not found for `Self`
+
+fn main() {}

src/test/ui/issues/issue-59029-1.stderr

@@ -0,0 +1,9 @@
+error[E0220]: associated type `Res` not found for `Self`
+  --> $DIR/issue-59029-1.rs:5:46
+   |
+LL | trait MkSvc<Target, Req> = Svc<Target> where Self::Res: Svc<Req>;
+   |                                              ^^^^^^^^^ associated type `Res` not found
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0220`.

src/test/ui/issues/issue-59029-2.rs

@@ -0,0 +1,8 @@
+// run-pass
+#![feature(trait_alias)]
+
+trait Svc<Req> { type Res; }
+
+trait MkSvc<Target, Req> = Svc<Target> where <Self as Svc<Target>>::Res: Svc<Req>;
+
+fn main() {}