From 7b480cdec6d6c046dc3cd86020f3762e37558cd4 Mon Sep 17 00:00:00 2001
From: Charles Gleason <charles_gleason@alumni.brown.edu>
Date: Tue, 1 Oct 2019 18:20:46 -0400
Subject: [PATCH 1/3] Implement Clone::clone_from for LinkedList

---
 src/liballoc/collections/linked_list.rs | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/src/liballoc/collections/linked_list.rs b/src/liballoc/collections/linked_list.rs
index 816a71f255798..998bcb87393b1 100644
--- a/src/liballoc/collections/linked_list.rs
+++ b/src/liballoc/collections/linked_list.rs
@@ -1197,6 +1197,19 @@ impl<T: Clone> Clone for LinkedList<T> {
     fn clone(&self) -> Self {
         self.iter().cloned().collect()
     }
+
+    fn clone_from(&mut self, other: &Self) {
+        let mut iter_other = other.iter();
+        if self.len() > other.len() {
+            self.split_off(other.len());
+        }
+        for elem in self.iter_mut() {
+            elem.clone_from(iter_other.next().unwrap());
+        }
+        if !iter_other.is_empty() {
+            self.extend(iter_other.cloned());
+        }
+    }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]

From 5055d4b1c6d7dedaec015e4ba9d96c94b1d978fd Mon Sep 17 00:00:00 2001
From: Charles Gleason <charles_gleason@alumni.brown.edu>
Date: Wed, 2 Oct 2019 11:29:12 -0400
Subject: [PATCH 2/3] Use zipped iterators in clone_from for LinkedList

---
 src/liballoc/collections/linked_list.rs | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/liballoc/collections/linked_list.rs b/src/liballoc/collections/linked_list.rs
index 998bcb87393b1..702df250999fb 100644
--- a/src/liballoc/collections/linked_list.rs
+++ b/src/liballoc/collections/linked_list.rs
@@ -1203,8 +1203,8 @@ impl<T: Clone> Clone for LinkedList<T> {
         if self.len() > other.len() {
             self.split_off(other.len());
         }
-        for elem in self.iter_mut() {
-            elem.clone_from(iter_other.next().unwrap());
+        for (elem, elem_other) in self.iter_mut().zip(&mut iter_other) {
+            elem.clone_from(elem_other);
         }
         if !iter_other.is_empty() {
             self.extend(iter_other.cloned());

From 864e6feaf857f4a48ace3eafd2003a32ac46602b Mon Sep 17 00:00:00 2001
From: Charles Gleason <charles_gleason@alumni.brown.edu>
Date: Wed, 2 Oct 2019 15:18:31 -0400
Subject: [PATCH 3/3] Add test for LinkedList clone_from

---
 src/liballoc/collections/linked_list/tests.rs | 43 +++++++++++++++++++
 1 file changed, 43 insertions(+)

diff --git a/src/liballoc/collections/linked_list/tests.rs b/src/liballoc/collections/linked_list/tests.rs
index ecb5948f11b36..1001f6bba3b82 100644
--- a/src/liballoc/collections/linked_list/tests.rs
+++ b/src/liballoc/collections/linked_list/tests.rs
@@ -110,6 +110,49 @@ fn test_append() {
     check_links(&n);
 }
 
+#[test]
+fn test_clone_from() {
+    // Short cloned from long
+    {
+        let v = vec![1, 2, 3, 4, 5];
+        let u = vec![8, 7, 6, 2, 3, 4, 5];
+        let mut m = list_from(&v);
+        let n = list_from(&u);
+        m.clone_from(&n);
+        check_links(&m);
+        assert_eq!(m, n);
+        for elt in u {
+            assert_eq!(m.pop_front(), Some(elt))
+        }
+    }
+    // Long cloned from short
+    {
+        let v = vec![1, 2, 3, 4, 5];
+        let u = vec![6, 7, 8];
+        let mut m = list_from(&v);
+        let n = list_from(&u);
+        m.clone_from(&n);
+        check_links(&m);
+        assert_eq!(m, n);
+        for elt in u {
+            assert_eq!(m.pop_front(), Some(elt))
+        }
+    }
+    // Two equal length lists
+    {
+        let v = vec![1, 2, 3, 4, 5];
+        let u = vec![9, 8, 1, 2, 3];
+        let mut m = list_from(&v);
+        let n = list_from(&u);
+        m.clone_from(&n);
+        check_links(&m);
+        assert_eq!(m, n);
+        for elt in u {
+            assert_eq!(m.pop_front(), Some(elt))
+        }
+    }
+}
+
 #[test]
 fn test_insert_prev() {
     let mut m = list_from(&[0, 2, 4, 6, 8]);