Clippy: Remove TyCtyt::super_traits_of public comment and test behavior

clippy_utils/src/ty.rs

@@ -949,16 +949,15 @@ pub fn ty_is_fn_once_param<'tcx>(tcx: TyCtxt<'_>, ty: Ty<'tcx>, predicates: &'tc
         .iter()
         .try_fold(false, |found, p| {
             if let ty::ClauseKind::Trait(p) = p.kind().skip_binder()
-            && let ty::Param(self_ty) = p.trait_ref.self_ty().kind()
-            && ty.index == self_ty.index
-        {
-            // This should use `super_traits_of`, but that's a private function.
-            if p.trait_ref.def_id == fn_once_id {
-                return Some(true);
-            } else if p.trait_ref.def_id == fn_mut_id || p.trait_ref.def_id == fn_id {
-                return None;
+                && let ty::Param(self_ty) = p.trait_ref.self_ty().kind()
+                && ty.index == self_ty.index
+            {
+                if p.trait_ref.def_id == fn_once_id {
+                    return Some(true);
+                } else if p.trait_ref.def_id == fn_mut_id || p.trait_ref.def_id == fn_id {
+                    return None;
+                }
             }
-        }
             Some(found)
         })
         .unwrap_or(false)

tests/ui/while_let_on_iterator.fixed

@@ -442,7 +442,20 @@ fn fn_once_closure() {
                 break;
             }
         }
-    })
+    });
+
+    // Lint if `FnOnce` is a super trait
+    trait MySpecialFnMut: FnOnce() {}
+    impl<T: FnOnce()> MySpecialFnMut for T {}
+    fn f4(_: impl MySpecialFnMut) {}
+    let mut it = 0..10;
+    f4(|| {
+        for x in it {
+            if x % 2 == 0 {
+                break;
+            }
+        }
+    });
 }
 
 fn main() {

tests/ui/while_let_on_iterator.rs

@@ -442,7 +442,20 @@ fn fn_once_closure() {
                 break;
             }
         }
-    })
+    });
+
+    // Lint if `FnOnce` is a super trait
+    trait MySpecialFnMut: FnOnce() {}
+    impl<T: FnOnce()> MySpecialFnMut for T {}
+    fn f4(_: impl MySpecialFnMut) {}
+    let mut it = 0..10;
+    f4(|| {
+        while let Some(x) = it.next() {
+            if x % 2 == 0 {
+                break;
+            }
+        }
+    });
 }
 
 fn main() {

tests/ui/while_let_on_iterator.stderr

@@ -151,10 +151,16 @@ LL |         while let Some(x) = it.next() {
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `for x in it`
 
 error: this loop could be written as a `for` loop
-  --> $DIR/while_let_on_iterator.rs:450:5
+  --> $DIR/while_let_on_iterator.rs:453:9
+   |
+LL |         while let Some(x) = it.next() {
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `for x in it`
+
+error: this loop could be written as a `for` loop
+  --> $DIR/while_let_on_iterator.rs:463:5
    |
 LL |     while let Some(..) = it.next() {
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `for _ in it`
 
-error: aborting due to 26 previous errors
+error: aborting due to 27 previous errors