From 40d3f2d7ef5835317fe9df9ecc01f4c363def4fd Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Sebastian=20Dr=C3=B6ge?= <sebastian@centricular.com>
Date: Thu, 4 Feb 2021 10:23:01 +0200
Subject: [PATCH] Increment `self.index` before calling
 `Iterator::self.a.__iterator_get_unchecked` in `Zip` `TrustedRandomAccess`
 specialization

Otherwise if `Iterator::self.a.__iterator_get_unchecked` panics the
index would not have been incremented yet and another call to
`Iterator::next` would read from the same index again, which is not
allowed according to the API contract of `TrustedRandomAccess` for
`!Clone`.

Fixes https://github.com/rust-lang/rust/issues/81740

(cherry picked from commit 86a4b27475aab52b998c15f5758540697cc9cff0)
---
 library/core/src/iter/adapters/zip.rs | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/library/core/src/iter/adapters/zip.rs b/library/core/src/iter/adapters/zip.rs
index 98b8dca96140..9f9835345200 100644
--- a/library/core/src/iter/adapters/zip.rs
+++ b/library/core/src/iter/adapters/zip.rs
@@ -198,12 +198,13 @@ fn next(&mut self) -> Option<(A::Item, B::Item)> {
                 Some((self.a.__iterator_get_unchecked(i), self.b.__iterator_get_unchecked(i)))
             }
         } else if A::may_have_side_effect() && self.index < self.a.size() {
+            let i = self.index;
+            self.index += 1;
             // match the base implementation's potential side effects
-            // SAFETY: we just checked that `self.index` < `self.a.len()`
+            // SAFETY: we just checked that `i` < `self.a.len()`
             unsafe {
-                self.a.__iterator_get_unchecked(self.index);
+                self.a.__iterator_get_unchecked(i);
             }
-            self.index += 1;
             None
         } else {
             None
-- 
2.31.1