From 10384ab18a386e6f7b58c714def62e405182d968 Mon Sep 17 00:00:00 2001
From: Jacob Kiesel <kieseljake@gmail.com>
Date: Mon, 18 Sep 2017 10:15:17 -0600
Subject: [PATCH] Add requested comment

---
 src/liballoc/vec.rs | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/src/liballoc/vec.rs b/src/liballoc/vec.rs
index cc0a60e747e6b..c5aaaac8f76be 100644
--- a/src/liballoc/vec.rs
+++ b/src/liballoc/vec.rs
@@ -2694,6 +2694,9 @@ impl<'a, T, F> Iterator for DrainFilter<'a, T, F>
                     let del = self.del;
                     let src: *const T = &v[i];
                     let dst: *mut T = &mut v[i - del];
+                    // This is safe because self.vec has length 0
+                    // thus its elements will not have Drop::drop
+                    // called on them in the event of a panic.
                     ptr::copy_nonoverlapping(src, dst, 1);
                 }
             }