From f21a98d8a9b6343effc4743dbb95507778181937 Mon Sep 17 00:00:00 2001
From: Oliver Schneider <github35764891676564198441@oli-obk.de>
Date: Wed, 27 Jun 2018 11:41:21 +0200
Subject: [PATCH] Explain the lack of item recursion

---
 src/librustc/hir/intravisit.rs | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/src/librustc/hir/intravisit.rs b/src/librustc/hir/intravisit.rs
index f2d1678d3369..e06563f90e00 100644
--- a/src/librustc/hir/intravisit.rs
+++ b/src/librustc/hir/intravisit.rs
@@ -608,6 +608,9 @@ pub fn walk_ty<'v, V: Visitor<'v>>(visitor: &mut V, typ: &'v Ty) {
             visitor.visit_lifetime(lifetime);
         }
         TyImplTraitExistential(_, def_id, ref lifetimes) => {
+            // we are not recursing into the `existential` item, because it is already being visited
+            // as part of the surrounding module. The `NodeId` just exists so we don't have to look
+            // it up everywhere else in the compiler
             visitor.visit_def_mention(Def::Existential(def_id));
             walk_list!(visitor, visit_lifetime, lifetimes);
         }