Add regression test for HRTB projection in closure

tests/ui/higher-ranked/hrtb-projection-closure-return-34430.rs

@@ -0,0 +1,41 @@
+//! Regression test for <https://github.com/rust-lang/rust/issues/34430>.
+//!
+//! An associated-type projection under a higher-ranked binder
+//! (`for<'a> FnOnce(&'a Foo) -> <T as WithLifetime<'a>>::Type`) failed to normalize,
+//! so returning `&'a Foo` from the closure was rejected even though
+//! `<FooRef as WithLifetime<'a>>::Type` *is* `&'a Foo`.
+
+//@ revisions: current next
+//@ ignore-compare-mode-next-solver (explicit revisions)
+//@[next] compile-flags: -Znext-solver
+//@ check-pass
+
+#![allow(unused)]
+
+trait WithLifetime<'a> {
+    type Type;
+}
+
+struct Foo;
+
+enum FooRef {}
+
+impl<'a> WithLifetime<'a> for FooRef {
+    type Type = &'a Foo;
+}
+
+fn wub<T, F>(f: F)
+where
+    T: for<'a> WithLifetime<'a>,
+    F: for<'a> FnOnce(&'a Foo) -> <T as WithLifetime<'a>>::Type,
+{
+}
+
+fn main() {
+    wub::<FooRef, _>(|foo| foo);
+
+    // Annotating the closure's return type used to ICE instead. Both the concrete
+    // and the projected spelling are checked, since either could regress alone.
+    wub::<FooRef, _>(|foo| -> &Foo { foo });
+    wub::<FooRef, _>(|foo| -> <FooRef as WithLifetime>::Type { foo });
+}