Add a couple tests for #90887 fixes

Author: aliemjay

src/test/ui/higher-rank-trait-bounds/normalize-under-binder/issue-56556.rs

@@ -11,3 +11,20 @@ where
 fn main() {
     foo::<Vec<u32>>(vec![]);
 }
+
+mod another {
+    use std::ops::Deref;
+
+    fn test<T, TDeref>()
+    where
+        T: Deref<Target = TDeref>,
+        TDeref: ?Sized,
+        for<'a> &'a TDeref: IntoIterator,
+        for<'a> <&'a TDeref as IntoIterator>::IntoIter: Clone,
+    {
+    }
+
+    fn main() {
+        test::<Vec<u8>, _>();
+    }
+}

src/test/ui/higher-rank-trait-bounds/normalize-under-binder/issue-90875.rs

@@ -0,0 +1,31 @@
+// check-pass
+
+trait Variable<'a> {
+    type Type;
+}
+
+impl Variable<'_> for () {
+    type Type = ();
+}
+
+fn check<F, T>(_: F)
+where
+    F: Fn(T), // <- if removed, all fn_* then require type annotations
+    F: for<'a> Fn(<T as Variable<'a>>::Type),
+    T: for<'a> Variable<'a>,
+{
+}
+
+fn test(arg: impl Fn(())) {
+    fn fn_1(_: ()) {}
+    let fn_2 = |_: ()| ();
+    let fn_3 = |a| fn_1(a);
+    let fn_4 = arg;
+
+    check(fn_1); // Error
+    check(fn_2); // Ok
+    check(fn_3); // Ok
+    check(fn_4); // Error
+}
+
+fn main() {}