From 4ade06bab8e9a3bf36a50aaaeb03dbb34dca0d71 Mon Sep 17 00:00:00 2001
From: Stein Somers <git@steinsomers.be>
Date: Fri, 10 Apr 2020 10:05:47 +0200
Subject: [PATCH] Rearrange BTreeMap::into_iter to match range_mut.

---
 src/liballoc/collections/btree/map.rs | 24 ++++++++++++------------
 1 file changed, 12 insertions(+), 12 deletions(-)

diff --git a/src/liballoc/collections/btree/map.rs b/src/liballoc/collections/btree/map.rs
index a1e59b2e6af..d00c0cb413f 100644
--- a/src/liballoc/collections/btree/map.rs
+++ b/src/liballoc/collections/btree/map.rs
@@ -1544,19 +1544,19 @@ impl<K, V> IntoIterator for BTreeMap<K, V> {
     type IntoIter = IntoIter<K, V>;
 
     fn into_iter(self) -> IntoIter<K, V> {
-        let me = ManuallyDrop::new(self);
-        if me.root.is_none() {
-            return IntoIter { front: None, back: None, length: 0 };
-        }
+        let mut me = ManuallyDrop::new(self);
+        if let Some(root) = me.root.as_mut() {
+            let root1 = unsafe { ptr::read(root).into_ref() };
+            let root2 = unsafe { ptr::read(root).into_ref() };
+            let len = me.length;
 
-        let root1 = unsafe { unwrap_unchecked(ptr::read(&me.root)).into_ref() };
-        let root2 = unsafe { unwrap_unchecked(ptr::read(&me.root)).into_ref() };
-        let len = me.length;
-
-        IntoIter {
-            front: Some(root1.first_leaf_edge()),
-            back: Some(root2.last_leaf_edge()),
-            length: len,
+            IntoIter {
+                front: Some(root1.first_leaf_edge()),
+                back: Some(root2.last_leaf_edge()),
+                length: len,
+            }
+        } else {
+            IntoIter { front: None, back: None, length: 0 }
         }
     }
 }