Add another regression test

Author: oli-obk

src/test/ui/impl-trait/issues/issue-93788.rs

@@ -0,0 +1,27 @@
+// check-pass
+
+struct D;
+
+trait Tr {
+    type It;
+    fn foo(self) -> Option<Self::It>;
+}
+
+impl<'a> Tr for &'a D {
+    type It = ();
+    fn foo(self) -> Option<()> { None }
+}
+
+fn run<F>(f: F)
+    where for<'a> &'a D: Tr,
+          F: Fn(<&D as Tr>::It),
+{
+    let d = &D;
+    while let Some(i) = d.foo() {
+        f(i);
+    }
+}
+
+fn main() {
+    run(|_| {});
+}