Add regression test for HRTB associated type projection closure

tests/ui/higher-ranked/hrtb-projection-closure-62201.rs

@@ -0,0 +1,42 @@
+//! Regression test for <https://github.com/rust-lang/rust/issues/62201>.
+//!
+//! A closure whose parameter type is a higher-ranked associated-type projection
+//! (`for<'r> Fn(<Self as Ty<'r>>::V)`) used to be wrongly rejected. It should compile.
+
+//@ check-pass
+
+#![allow(unused, unreachable_code)]
+
+trait Ty<'a> {
+    type V;
+}
+
+trait SIter: for<'a> Ty<'a> {
+    fn f<F>(&self, f: F)
+    where
+        F: for<'r> Fn(<Self as Ty<'r>>::V);
+}
+
+struct S<I>(I);
+
+impl<'a, I: Ty<'a>> Ty<'a> for S<I> {
+    type V = <I as Ty<'a>>::V;
+}
+
+impl<I: SIter, Item> SIter for S<I>
+where
+    for<'r> S<I>: Ty<'r, V = Item>,
+    for<'r> I: Ty<'r, V = Item>,
+{
+    fn f<F>(&self, f: F)
+    where
+        F: Fn(<Self as Ty>::V),
+    {
+        self.0.f(|item| {
+            let item: <Self as Ty>::V = loop {};
+            f(item)
+        })
+    }
+}
+
+fn main() {}