From 1f61f36849249b5333c74f63d54d2f8bfe30ad59 Mon Sep 17 00:00:00 2001
From: Jonas Schievink <jonasschievink@gmail.com>
Date: Thu, 29 Aug 2019 14:11:55 +0200
Subject: [PATCH] Add comment about the shallow subst rule

---
 src/librustc_typeck/check/wfcheck.rs | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/src/librustc_typeck/check/wfcheck.rs b/src/librustc_typeck/check/wfcheck.rs
index 9f1ae37da1a..e39beb547d1 100644
--- a/src/librustc_typeck/check/wfcheck.rs
+++ b/src/librustc_typeck/check/wfcheck.rs
@@ -482,6 +482,9 @@ fn check_associated_type_defaults(
     /// substitution forces the trait to add a `B: Clone` bound to be accepted,
     /// which means that an `impl` can replace any default without breaking
     /// others.
+    ///
+    /// Note that this isn't needed for soundness: The defaults would still be
+    /// checked in any impl that doesn't override them.
     struct DefaultNormalizer<'tcx> {
         tcx: TyCtxt<'tcx>,
         map: FxHashMap<ty::ProjectionTy<'tcx>, Ty<'tcx>>,
-- 
2.44.0