diff --git a/library/alloc/benches/btree/map.rs b/library/alloc/benches/btree/map.rs
index 21a0fb844e8..920a5ca7db0 100644
--- a/library/alloc/benches/btree/map.rs
+++ b/library/alloc/benches/btree/map.rs
@@ -177,7 +177,7 @@ pub fn iteration_mut_100000(b: &mut Bencher) {
     bench_iteration_mut(b, 100000);
 }
 
-fn bench_first_and_last(b: &mut Bencher, size: i32) {
+fn bench_first_and_last_nightly(b: &mut Bencher, size: i32) {
     let map: BTreeMap<_, _> = (0..size).map(|i| (i, i)).collect();
     b.iter(|| {
         for _ in 0..10 {
@@ -187,19 +187,44 @@ fn bench_first_and_last(b: &mut Bencher, size: i32) {
     });
 }
 
-#[bench]
-pub fn first_and_last_0(b: &mut Bencher) {
-    bench_first_and_last(b, 0);
+fn bench_first_and_last_stable(b: &mut Bencher, size: i32) {
+    let map: BTreeMap<_, _> = (0..size).map(|i| (i, i)).collect();
+    b.iter(|| {
+        for _ in 0..10 {
+            black_box(map.iter().next());
+            black_box(map.iter().next_back());
+        }
+    });
 }
 
 #[bench]
-pub fn first_and_last_100(b: &mut Bencher) {
-    bench_first_and_last(b, 100);
+pub fn first_and_last_0_nightly(b: &mut Bencher) {
+    bench_first_and_last_nightly(b, 0);
 }
 
 #[bench]
-pub fn first_and_last_10k(b: &mut Bencher) {
-    bench_first_and_last(b, 10_000);
+pub fn first_and_last_0_stable(b: &mut Bencher) {
+    bench_first_and_last_stable(b, 0);
+}
+
+#[bench]
+pub fn first_and_last_100_nightly(b: &mut Bencher) {
+    bench_first_and_last_nightly(b, 100);
+}
+
+#[bench]
+pub fn first_and_last_100_stable(b: &mut Bencher) {
+    bench_first_and_last_stable(b, 100);
+}
+
+#[bench]
+pub fn first_and_last_10k_nightly(b: &mut Bencher) {
+    bench_first_and_last_nightly(b, 10_000);
+}
+
+#[bench]
+pub fn first_and_last_10k_stable(b: &mut Bencher) {
+    bench_first_and_last_stable(b, 10_000);
 }
 
 const BENCH_RANGE_SIZE: i32 = 145;
diff --git a/library/alloc/src/collections/btree/map.rs b/library/alloc/src/collections/btree/map.rs
index 30194aa446f..d7519c6d093 100644
--- a/library/alloc/src/collections/btree/map.rs
+++ b/library/alloc/src/collections/btree/map.rs
@@ -1299,7 +1299,7 @@ impl<'a, K: 'a, V: 'a> Iterator for Iter<'a, K, V> {
             None
         } else {
             self.length -= 1;
-            Some(unsafe { self.range.next_unchecked() })
+            Some(unsafe { self.range.inner.next_unchecked() })
         }
     }
 
@@ -1330,7 +1330,7 @@ impl<'a, K: 'a, V: 'a> DoubleEndedIterator for Iter<'a, K, V> {
             None
         } else {
             self.length -= 1;
-            Some(unsafe { self.range.next_back_unchecked() })
+            Some(unsafe { self.range.inner.next_back_unchecked() })
         }
     }
 }
@@ -1368,7 +1368,7 @@ impl<'a, K: 'a, V: 'a> Iterator for IterMut<'a, K, V> {
             None
         } else {
             self.length -= 1;
-            Some(unsafe { self.range.next_unchecked() })
+            Some(unsafe { self.range.inner.next_unchecked() })
         }
     }
 
@@ -1396,7 +1396,7 @@ impl<'a, K: 'a, V: 'a> DoubleEndedIterator for IterMut<'a, K, V> {
             None
         } else {
             self.length -= 1;
-            Some(unsafe { self.range.next_back_unchecked() })
+            Some(unsafe { self.range.inner.next_back_unchecked() })
         }
     }
 }
@@ -1475,7 +1475,7 @@ impl<K, V> Drop for Dropper<K, V> {
 #[stable(feature = "btree_drop", since = "1.7.0")]
 impl<K, V> Drop for IntoIter<K, V> {
     fn drop(&mut self) {
-        if let Some(front) = self.range.front.take() {
+        if let Some(front) = self.range.take_front() {
             Dropper { front, remaining_length: self.length };
         }
     }
@@ -1490,8 +1490,7 @@ impl<K, V> Iterator for IntoIter<K, V> {
             None
         } else {
             self.length -= 1;
-            let front = self.range.front.as_mut().unwrap();
-            let kv = unsafe { front.deallocating_next_unchecked() };
+            let kv = unsafe { self.range.deallocating_next_unchecked() };
             Some(kv.into_key_val())
         }
     }
@@ -1508,8 +1507,7 @@ impl<K, V> DoubleEndedIterator for IntoIter<K, V> {
             None
         } else {
             self.length -= 1;
-            let back = self.range.back.as_mut().unwrap();
-            let kv = unsafe { back.deallocating_next_back_unchecked() };
+            let kv = unsafe { self.range.deallocating_next_back_unchecked() };
             Some(kv.into_key_val())
         }
     }
@@ -1727,7 +1725,7 @@ impl<'a, K, V> Iterator for Range<'a, K, V> {
     type Item = (&'a K, &'a V);
 
     fn next(&mut self) -> Option<(&'a K, &'a V)> {
-        if self.inner.is_empty() { None } else { Some(unsafe { self.next_unchecked() }) }
+        self.inner.next_checked()
     }
 
     fn last(mut self) -> Option<(&'a K, &'a V)> {
@@ -1777,12 +1775,6 @@ impl<K, V> ExactSizeIterator for ValuesMut<'_, K, V> {
 #[stable(feature = "fused", since = "1.26.0")]
 impl<K, V> FusedIterator for ValuesMut<'_, K, V> {}
 
-impl<'a, K, V> Range<'a, K, V> {
-    unsafe fn next_unchecked(&mut self) -> (&'a K, &'a V) {
-        unsafe { self.inner.front.as_mut().unwrap_unchecked().next_unchecked() }
-    }
-}
-
 #[stable(feature = "map_into_keys_values", since = "1.54.0")]
 impl<K, V> Iterator for IntoKeys<K, V> {
     type Item = K;
@@ -1862,13 +1854,7 @@ impl<K, V> FusedIterator for IntoValues<K, V> {}
 #[stable(feature = "btree_range", since = "1.17.0")]
 impl<'a, K, V> DoubleEndedIterator for Range<'a, K, V> {
     fn next_back(&mut self) -> Option<(&'a K, &'a V)> {
-        if self.inner.is_empty() { None } else { Some(unsafe { self.next_back_unchecked() }) }
-    }
-}
-
-impl<'a, K, V> Range<'a, K, V> {
-    unsafe fn next_back_unchecked(&mut self) -> (&'a K, &'a V) {
-        unsafe { self.inner.back.as_mut().unwrap_unchecked().next_back_unchecked() }
+        self.inner.next_back_checked()
     }
 }
 
@@ -1878,7 +1864,7 @@ impl<K, V> FusedIterator for Range<'_, K, V> {}
 #[stable(feature = "btree_range", since = "1.17.0")]
 impl<K, V> Clone for Range<'_, K, V> {
     fn clone(&self) -> Self {
-        Range { inner: LeafRange { front: self.inner.front, back: self.inner.back } }
+        Range { inner: self.inner.clone() }
     }
 }
 
@@ -1887,7 +1873,7 @@ impl<'a, K, V> Iterator for RangeMut<'a, K, V> {
     type Item = (&'a K, &'a mut V);
 
     fn next(&mut self) -> Option<(&'a K, &'a mut V)> {
-        if self.inner.is_empty() { None } else { Some(unsafe { self.next_unchecked() }) }
+        self.inner.next_checked()
     }
 
     fn last(mut self) -> Option<(&'a K, &'a mut V)> {
@@ -1904,10 +1890,6 @@ impl<'a, K, V> Iterator for RangeMut<'a, K, V> {
 }
 
 impl<'a, K, V> RangeMut<'a, K, V> {
-    unsafe fn next_unchecked(&mut self) -> (&'a K, &'a mut V) {
-        unsafe { self.inner.front.as_mut().unwrap_unchecked().next_unchecked() }
-    }
-
     /// Returns an iterator of references over the remaining items.
     #[inline]
     pub(super) fn iter(&self) -> Range<'_, K, V> {
@@ -1918,19 +1900,13 @@ impl<'a, K, V> RangeMut<'a, K, V> {
 #[stable(feature = "btree_range", since = "1.17.0")]
 impl<'a, K, V> DoubleEndedIterator for RangeMut<'a, K, V> {
     fn next_back(&mut self) -> Option<(&'a K, &'a mut V)> {
-        if self.inner.is_empty() { None } else { Some(unsafe { self.next_back_unchecked() }) }
+        self.inner.next_back_checked()
     }
 }
 
 #[stable(feature = "fused", since = "1.26.0")]
 impl<K, V> FusedIterator for RangeMut<'_, K, V> {}
 
-impl<'a, K, V> RangeMut<'a, K, V> {
-    unsafe fn next_back_unchecked(&mut self) -> (&'a K, &'a mut V) {
-        unsafe { self.inner.back.as_mut().unwrap_unchecked().next_back_unchecked() }
-    }
-}
-
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<K: Ord, V> FromIterator<(K, V)> for BTreeMap<K, V> {
     fn from_iter<T: IntoIterator<Item = (K, V)>>(iter: T) -> BTreeMap<K, V> {
diff --git a/library/alloc/src/collections/btree/navigate.rs b/library/alloc/src/collections/btree/navigate.rs
index 563c070dd0f..17568f7b005 100644
--- a/library/alloc/src/collections/btree/navigate.rs
+++ b/library/alloc/src/collections/btree/navigate.rs
@@ -4,9 +4,16 @@ use core::ptr;
 
 use super::node::{marker, ForceResult::*, Handle, NodeRef};
 
+// `front` and `back` are always both `None` or both `Some`.
 pub struct LeafRange<BorrowType, K, V> {
-    pub front: Option<Handle<NodeRef<BorrowType, K, V, marker::Leaf>, marker::Edge>>,
-    pub back: Option<Handle<NodeRef<BorrowType, K, V, marker::Leaf>, marker::Edge>>,
+    front: Option<Handle<NodeRef<BorrowType, K, V, marker::Leaf>, marker::Edge>>,
+    back: Option<Handle<NodeRef<BorrowType, K, V, marker::Leaf>, marker::Edge>>,
+}
+
+impl<'a, K: 'a, V: 'a> Clone for LeafRange<marker::Immut<'a>, K, V> {
+    fn clone(&self) -> Self {
+        LeafRange { front: self.front.clone(), back: self.back.clone() }
+    }
 }
 
 impl<BorrowType, K, V> LeafRange<BorrowType, K, V> {
@@ -14,7 +21,7 @@ impl<BorrowType, K, V> LeafRange<BorrowType, K, V> {
         LeafRange { front: None, back: None }
     }
 
-    pub fn is_empty(&self) -> bool {
+    fn is_empty(&self) -> bool {
         self.front == self.back
     }
 
@@ -27,6 +34,81 @@ impl<BorrowType, K, V> LeafRange<BorrowType, K, V> {
     }
 }
 
+impl<'a, K, V> LeafRange<marker::Immut<'a>, K, V> {
+    #[inline]
+    pub fn next_checked(&mut self) -> Option<(&'a K, &'a V)> {
+        if self.is_empty() { None } else { Some(unsafe { self.next_unchecked() }) }
+    }
+
+    #[inline]
+    pub fn next_back_checked(&mut self) -> Option<(&'a K, &'a V)> {
+        if self.is_empty() { None } else { Some(unsafe { self.next_back_unchecked() }) }
+    }
+
+    #[inline]
+    pub unsafe fn next_unchecked(&mut self) -> (&'a K, &'a V) {
+        debug_assert!(self.front.is_some());
+        unsafe { self.front.as_mut().unwrap_unchecked().next_unchecked() }
+    }
+
+    #[inline]
+    pub unsafe fn next_back_unchecked(&mut self) -> (&'a K, &'a V) {
+        debug_assert!(self.back.is_some());
+        unsafe { self.back.as_mut().unwrap_unchecked().next_back_unchecked() }
+    }
+}
+
+impl<'a, K, V> LeafRange<marker::ValMut<'a>, K, V> {
+    #[inline]
+    pub fn next_checked(&mut self) -> Option<(&'a K, &'a mut V)> {
+        if self.is_empty() { None } else { Some(unsafe { self.next_unchecked() }) }
+    }
+
+    #[inline]
+    pub fn next_back_checked(&mut self) -> Option<(&'a K, &'a mut V)> {
+        if self.is_empty() { None } else { Some(unsafe { self.next_back_unchecked() }) }
+    }
+
+    #[inline]
+    pub unsafe fn next_unchecked(&mut self) -> (&'a K, &'a mut V) {
+        debug_assert!(self.front.is_some());
+        unsafe { self.front.as_mut().unwrap_unchecked().next_unchecked() }
+    }
+
+    #[inline]
+    pub unsafe fn next_back_unchecked(&mut self) -> (&'a K, &'a mut V) {
+        debug_assert!(self.back.is_some());
+        unsafe { self.back.as_mut().unwrap_unchecked().next_back_unchecked() }
+    }
+}
+
+impl<K, V> LeafRange<marker::Dying, K, V> {
+    #[inline]
+    pub fn take_front(
+        &mut self,
+    ) -> Option<Handle<NodeRef<marker::Dying, K, V, marker::Leaf>, marker::Edge>> {
+        self.front.take()
+    }
+
+    #[inline]
+    pub unsafe fn deallocating_next_unchecked(
+        &mut self,
+    ) -> Handle<NodeRef<marker::Dying, K, V, marker::LeafOrInternal>, marker::KV> {
+        debug_assert!(self.front.is_some());
+        let front = self.front.as_mut().unwrap();
+        unsafe { front.deallocating_next_unchecked() }
+    }
+
+    #[inline]
+    pub unsafe fn deallocating_next_back_unchecked(
+        &mut self,
+    ) -> Handle<NodeRef<marker::Dying, K, V, marker::LeafOrInternal>, marker::KV> {
+        debug_assert!(self.back.is_some());
+        let back = self.back.as_mut().unwrap();
+        unsafe { back.deallocating_next_back_unchecked() }
+    }
+}
+
 impl<BorrowType: marker::BorrowType, K, V> NodeRef<BorrowType, K, V, marker::LeafOrInternal> {
     /// Finds the distinct leaf edges delimiting a specified range in a tree.
     ///
@@ -36,7 +118,7 @@ impl<BorrowType: marker::BorrowType, K, V> NodeRef<BorrowType, K, V, marker::Lea
     /// result will eventually reach the same edge.
     ///
     /// If there are no such edges, i.e., if the tree contains no key within
-    /// the range, returns a pair of empty options.
+    /// the range, returns an empty `front` and `back`.
     ///
     /// # Safety
     /// Unless `BorrowType` is `Immut`, do not use the handles to visit the same
@@ -191,7 +273,7 @@ impl<BorrowType: marker::BorrowType, K, V>
     /// Given a leaf edge handle, returns [`Result::Ok`] with a handle to the neighboring KV
     /// on the left side, which is either in the same leaf node or in an ancestor node.
     /// If the leaf edge is the first one in the tree, returns [`Result::Err`] with the root node.
-    pub fn next_back_kv(
+    fn next_back_kv(
         self,
     ) -> Result<
         Handle<NodeRef<BorrowType, K, V, marker::LeafOrInternal>, marker::KV>,
@@ -216,7 +298,7 @@ impl<BorrowType: marker::BorrowType, K, V>
     /// Given an internal edge handle, returns [`Result::Ok`] with a handle to the neighboring KV
     /// on the right side, which is either in the same internal node or in an ancestor node.
     /// If the internal edge is the last one in the tree, returns [`Result::Err`] with the root node.
-    pub fn next_kv(
+    fn next_kv(
         self,
     ) -> Result<
         Handle<NodeRef<BorrowType, K, V, marker::Internal>, marker::KV>,
@@ -250,7 +332,7 @@ impl<K, V> Handle<NodeRef<marker::Dying, K, V, marker::Leaf>, marker::Edge> {
     /// - The returned KV handle is only valid to access the key and value,
     ///   and only valid until the next call to this method or counterpart
     ///   `deallocating_next_back`.
-    pub unsafe fn deallocating_next(
+    unsafe fn deallocating_next(
         self,
     ) -> Option<(Self, Handle<NodeRef<marker::Dying, K, V, marker::LeafOrInternal>, marker::KV>)>
     {
@@ -316,9 +398,10 @@ impl<'a, K, V> Handle<NodeRef<marker::Immut<'a>, K, V, marker::Leaf>, marker::Ed
     ///
     /// # Safety
     /// There must be another KV in the direction travelled.
-    pub unsafe fn next_unchecked(&mut self) -> (&'a K, &'a V) {
+    unsafe fn next_unchecked(&mut self) -> (&'a K, &'a V) {
         super::mem::replace(self, |leaf_edge| {
             let kv = leaf_edge.next_kv();
+            debug_assert!(kv.is_ok());
             let kv = unsafe { kv.ok().unwrap_unchecked() };
             (kv.next_leaf_edge(), kv.into_kv())
         })
@@ -329,9 +412,10 @@ impl<'a, K, V> Handle<NodeRef<marker::Immut<'a>, K, V, marker::Leaf>, marker::Ed
     ///
     /// # Safety
     /// There must be another KV in the direction travelled.
-    pub unsafe fn next_back_unchecked(&mut self) -> (&'a K, &'a V) {
+    unsafe fn next_back_unchecked(&mut self) -> (&'a K, &'a V) {
         super::mem::replace(self, |leaf_edge| {
             let kv = leaf_edge.next_back_kv();
+            debug_assert!(kv.is_ok());
             let kv = unsafe { kv.ok().unwrap_unchecked() };
             (kv.next_back_leaf_edge(), kv.into_kv())
         })
@@ -344,9 +428,10 @@ impl<'a, K, V> Handle<NodeRef<marker::ValMut<'a>, K, V, marker::Leaf>, marker::E
     ///
     /// # Safety
     /// There must be another KV in the direction travelled.
-    pub unsafe fn next_unchecked(&mut self) -> (&'a K, &'a mut V) {
+    unsafe fn next_unchecked(&mut self) -> (&'a K, &'a mut V) {
         let kv = super::mem::replace(self, |leaf_edge| {
             let kv = leaf_edge.next_kv();
+            debug_assert!(kv.is_ok());
             let kv = unsafe { kv.ok().unwrap_unchecked() };
             (unsafe { ptr::read(&kv) }.next_leaf_edge(), kv)
         });
@@ -359,9 +444,10 @@ impl<'a, K, V> Handle<NodeRef<marker::ValMut<'a>, K, V, marker::Leaf>, marker::E
     ///
     /// # Safety
     /// There must be another KV in the direction travelled.
-    pub unsafe fn next_back_unchecked(&mut self) -> (&'a K, &'a mut V) {
+    unsafe fn next_back_unchecked(&mut self) -> (&'a K, &'a mut V) {
         let kv = super::mem::replace(self, |leaf_edge| {
             let kv = leaf_edge.next_back_kv();
+            debug_assert!(kv.is_ok());
             let kv = unsafe { kv.ok().unwrap_unchecked() };
             (unsafe { ptr::read(&kv) }.next_back_leaf_edge(), kv)
         });
@@ -403,7 +489,7 @@ impl<K, V> Handle<NodeRef<marker::Dying, K, V, marker::Leaf>, marker::Edge> {
     ///
     /// The only safe way to proceed with the updated handle is to compare it, drop it,
     /// or call this method or counterpart `deallocating_next_unchecked` again.
-    pub unsafe fn deallocating_next_back_unchecked(
+    unsafe fn deallocating_next_back_unchecked(
         &mut self,
     ) -> Handle<NodeRef<marker::Dying, K, V, marker::LeafOrInternal>, marker::KV> {
         super::mem::replace(self, |leaf_edge| unsafe {
@@ -508,9 +594,7 @@ impl<BorrowType: marker::BorrowType, K, V>
     }
 
     /// Returns the leaf edge closest to a KV for backward navigation.
-    pub fn next_back_leaf_edge(
-        self,
-    ) -> Handle<NodeRef<BorrowType, K, V, marker::Leaf>, marker::Edge> {
+    fn next_back_leaf_edge(self) -> Handle<NodeRef<BorrowType, K, V, marker::Leaf>, marker::Edge> {
         match self.force() {
             Leaf(leaf_kv) => leaf_kv.left_edge(),
             Internal(internal_kv) => {
diff --git a/src/test/ui/variance/variance-btree-invariant-types.nll.stderr b/src/test/ui/variance/variance-btree-invariant-types.nll.stderr
index be18737b5f1..4b653238aa7 100644
--- a/src/test/ui/variance/variance-btree-invariant-types.nll.stderr
+++ b/src/test/ui/variance/variance-btree-invariant-types.nll.stderr
@@ -39,7 +39,47 @@ LL |     v
    = help: consider replacing `'new` with `'static`
 
 error: lifetime may not live long enough
-  --> $DIR/variance-btree-invariant-types.rs:18:5
+  --> $DIR/variance-btree-invariant-types.rs:17:5
+   |
+LL | fn range_cov_key<'a, 'new>(v: RangeMut<'a, &'static (), ()>) -> RangeMut<'a, &'new (), ()> {
+   |                      ---- lifetime `'new` defined here
+LL |     v
+   |     ^ returning this value requires that `'new` must outlive `'static`
+   |
+   = help: consider replacing `'new` with `'static`
+
+error: lifetime may not live long enough
+  --> $DIR/variance-btree-invariant-types.rs:20:5
+   |
+LL | fn range_cov_val<'a, 'new>(v: RangeMut<'a, (), &'static ()>) -> RangeMut<'a, (), &'new ()> {
+   |                      ---- lifetime `'new` defined here
+LL |     v
+   |     ^ returning this value requires that `'new` must outlive `'static`
+   |
+   = help: consider replacing `'new` with `'static`
+
+error: lifetime may not live long enough
+  --> $DIR/variance-btree-invariant-types.rs:23:5
+   |
+LL | fn range_contra_key<'a, 'new>(v: RangeMut<'a, &'new (), ()>) -> RangeMut<'a, &'static (), ()> {
+   |                         ---- lifetime `'new` defined here
+LL |     v
+   |     ^ returning this value requires that `'new` must outlive `'static`
+   |
+   = help: consider replacing `'new` with `'static`
+
+error: lifetime may not live long enough
+  --> $DIR/variance-btree-invariant-types.rs:26:5
+   |
+LL | fn range_contra_val<'a, 'new>(v: RangeMut<'a, (), &'new ()>) -> RangeMut<'a, (), &'static ()> {
+   |                         ---- lifetime `'new` defined here
+LL |     v
+   |     ^ returning this value requires that `'new` must outlive `'static`
+   |
+   = help: consider replacing `'new` with `'static`
+
+error: lifetime may not live long enough
+  --> $DIR/variance-btree-invariant-types.rs:31:5
    |
 LL | fn occ_cov_key<'a, 'new>(v: OccupiedEntry<'a, &'static (), ()>)
    |                    ---- lifetime `'new` defined here
@@ -50,7 +90,7 @@ LL |     v
    = help: consider replacing `'new` with `'static`
 
 error: lifetime may not live long enough
-  --> $DIR/variance-btree-invariant-types.rs:22:5
+  --> $DIR/variance-btree-invariant-types.rs:35:5
    |
 LL | fn occ_cov_val<'a, 'new>(v: OccupiedEntry<'a, (), &'static ()>)
    |                    ---- lifetime `'new` defined here
@@ -61,7 +101,7 @@ LL |     v
    = help: consider replacing `'new` with `'static`
 
 error: lifetime may not live long enough
-  --> $DIR/variance-btree-invariant-types.rs:26:5
+  --> $DIR/variance-btree-invariant-types.rs:39:5
    |
 LL | fn occ_contra_key<'a, 'new>(v: OccupiedEntry<'a, &'new (), ()>)
    |                       ---- lifetime `'new` defined here
@@ -72,7 +112,7 @@ LL |     v
    = help: consider replacing `'new` with `'static`
 
 error: lifetime may not live long enough
-  --> $DIR/variance-btree-invariant-types.rs:30:5
+  --> $DIR/variance-btree-invariant-types.rs:43:5
    |
 LL | fn occ_contra_val<'a, 'new>(v: OccupiedEntry<'a, (), &'new ()>)
    |                       ---- lifetime `'new` defined here
@@ -83,7 +123,7 @@ LL |     v
    = help: consider replacing `'new` with `'static`
 
 error: lifetime may not live long enough
-  --> $DIR/variance-btree-invariant-types.rs:35:5
+  --> $DIR/variance-btree-invariant-types.rs:48:5
    |
 LL | fn vac_cov_key<'a, 'new>(v: VacantEntry<'a, &'static (), ()>)
    |                    ---- lifetime `'new` defined here
@@ -94,7 +134,7 @@ LL |     v
    = help: consider replacing `'new` with `'static`
 
 error: lifetime may not live long enough
-  --> $DIR/variance-btree-invariant-types.rs:39:5
+  --> $DIR/variance-btree-invariant-types.rs:52:5
    |
 LL | fn vac_cov_val<'a, 'new>(v: VacantEntry<'a, (), &'static ()>)
    |                    ---- lifetime `'new` defined here
@@ -105,7 +145,7 @@ LL |     v
    = help: consider replacing `'new` with `'static`
 
 error: lifetime may not live long enough
-  --> $DIR/variance-btree-invariant-types.rs:43:5
+  --> $DIR/variance-btree-invariant-types.rs:56:5
    |
 LL | fn vac_contra_key<'a, 'new>(v: VacantEntry<'a, &'new (), ()>)
    |                       ---- lifetime `'new` defined here
@@ -116,7 +156,7 @@ LL |     v
    = help: consider replacing `'new` with `'static`
 
 error: lifetime may not live long enough
-  --> $DIR/variance-btree-invariant-types.rs:47:5
+  --> $DIR/variance-btree-invariant-types.rs:60:5
    |
 LL | fn vac_contra_val<'a, 'new>(v: VacantEntry<'a, (), &'new ()>)
    |                       ---- lifetime `'new` defined here
@@ -126,5 +166,5 @@ LL |     v
    |
    = help: consider replacing `'new` with `'static`
 
-error: aborting due to 12 previous errors
+error: aborting due to 16 previous errors
 
diff --git a/src/test/ui/variance/variance-btree-invariant-types.rs b/src/test/ui/variance/variance-btree-invariant-types.rs
index 2e5dc671db8..4549622f24a 100644
--- a/src/test/ui/variance/variance-btree-invariant-types.rs
+++ b/src/test/ui/variance/variance-btree-invariant-types.rs
@@ -1,4 +1,4 @@
-use std::collections::btree_map::{IterMut, OccupiedEntry, VacantEntry};
+use std::collections::btree_map::{IterMut, OccupiedEntry, RangeMut, VacantEntry};
 
 fn iter_cov_key<'a, 'new>(v: IterMut<'a, &'static (), ()>) -> IterMut<'a, &'new (), ()> {
     v //~ ERROR mismatched types
@@ -13,6 +13,19 @@ fn iter_contra_val<'a, 'new>(v: IterMut<'a, (), &'new ()>) -> IterMut<'a, (), &'
     v //~ ERROR mismatched types
 }
 
+fn range_cov_key<'a, 'new>(v: RangeMut<'a, &'static (), ()>) -> RangeMut<'a, &'new (), ()> {
+    v //~ ERROR mismatched types
+}
+fn range_cov_val<'a, 'new>(v: RangeMut<'a, (), &'static ()>) -> RangeMut<'a, (), &'new ()> {
+    v //~ ERROR mismatched types
+}
+fn range_contra_key<'a, 'new>(v: RangeMut<'a, &'new (), ()>) -> RangeMut<'a, &'static (), ()> {
+    v //~ ERROR mismatched types
+}
+fn range_contra_val<'a, 'new>(v: RangeMut<'a, (), &'new ()>) -> RangeMut<'a, (), &'static ()> {
+    v //~ ERROR mismatched types
+}
+
 fn occ_cov_key<'a, 'new>(v: OccupiedEntry<'a, &'static (), ()>)
                          -> OccupiedEntry<'a, &'new (), ()> {
     v //~ ERROR mismatched types
diff --git a/src/test/ui/variance/variance-btree-invariant-types.stderr b/src/test/ui/variance/variance-btree-invariant-types.stderr
index 8172a019b65..ba47bdff281 100644
--- a/src/test/ui/variance/variance-btree-invariant-types.stderr
+++ b/src/test/ui/variance/variance-btree-invariant-types.stderr
@@ -59,33 +59,48 @@ LL | fn iter_contra_val<'a, 'new>(v: IterMut<'a, (), &'new ()>) -> IterMut<'a, (
    = note: ...does not necessarily outlive the static lifetime
 
 error[E0308]: mismatched types
-  --> $DIR/variance-btree-invariant-types.rs:18:5
+  --> $DIR/variance-btree-invariant-types.rs:17:5
    |
 LL |     v
    |     ^ lifetime mismatch
    |
-   = note: expected struct `std::collections::btree_map::OccupiedEntry<'_, &'new (), _>`
-              found struct `std::collections::btree_map::OccupiedEntry<'_, &'static (), _>`
-note: the lifetime `'new` as defined on the function body at 16:20...
-  --> $DIR/variance-btree-invariant-types.rs:16:20
+   = note: expected struct `RangeMut<'_, &'new (), _>`
+              found struct `RangeMut<'_, &'static (), _>`
+note: the lifetime `'new` as defined on the function body at 16:22...
+  --> $DIR/variance-btree-invariant-types.rs:16:22
    |
-LL | fn occ_cov_key<'a, 'new>(v: OccupiedEntry<'a, &'static (), ()>)
-   |                    ^^^^
+LL | fn range_cov_key<'a, 'new>(v: RangeMut<'a, &'static (), ()>) -> RangeMut<'a, &'new (), ()> {
+   |                      ^^^^
    = note: ...does not necessarily outlive the static lifetime
 
 error[E0308]: mismatched types
-  --> $DIR/variance-btree-invariant-types.rs:22:5
+  --> $DIR/variance-btree-invariant-types.rs:20:5
    |
 LL |     v
    |     ^ lifetime mismatch
    |
-   = note: expected struct `std::collections::btree_map::OccupiedEntry<'_, _, &'new ()>`
-              found struct `std::collections::btree_map::OccupiedEntry<'_, _, &'static ()>`
-note: the lifetime `'new` as defined on the function body at 20:20...
-  --> $DIR/variance-btree-invariant-types.rs:20:20
+   = note: expected struct `RangeMut<'_, _, &'new ()>`
+              found struct `RangeMut<'_, _, &'static ()>`
+note: the lifetime `'new` as defined on the function body at 19:22...
+  --> $DIR/variance-btree-invariant-types.rs:19:22
    |
-LL | fn occ_cov_val<'a, 'new>(v: OccupiedEntry<'a, (), &'static ()>)
-   |                    ^^^^
+LL | fn range_cov_val<'a, 'new>(v: RangeMut<'a, (), &'static ()>) -> RangeMut<'a, (), &'new ()> {
+   |                      ^^^^
+   = note: ...does not necessarily outlive the static lifetime
+
+error[E0308]: mismatched types
+  --> $DIR/variance-btree-invariant-types.rs:23:5
+   |
+LL |     v
+   |     ^ lifetime mismatch
+   |
+   = note: expected struct `RangeMut<'_, &'static (), _>`
+              found struct `RangeMut<'_, &'new (), _>`
+note: the lifetime `'new` as defined on the function body at 22:25...
+  --> $DIR/variance-btree-invariant-types.rs:22:25
+   |
+LL | fn range_contra_key<'a, 'new>(v: RangeMut<'a, &'new (), ()>) -> RangeMut<'a, &'static (), ()> {
+   |                         ^^^^
    = note: ...does not necessarily outlive the static lifetime
 
 error[E0308]: mismatched types
@@ -94,28 +109,28 @@ error[E0308]: mismatched types
 LL |     v
    |     ^ lifetime mismatch
    |
-   = note: expected struct `std::collections::btree_map::OccupiedEntry<'_, &'static (), _>`
-              found struct `std::collections::btree_map::OccupiedEntry<'_, &'new (), _>`
-note: the lifetime `'new` as defined on the function body at 24:23...
-  --> $DIR/variance-btree-invariant-types.rs:24:23
+   = note: expected struct `RangeMut<'_, _, &'static ()>`
+              found struct `RangeMut<'_, _, &'new ()>`
+note: the lifetime `'new` as defined on the function body at 25:25...
+  --> $DIR/variance-btree-invariant-types.rs:25:25
    |
-LL | fn occ_contra_key<'a, 'new>(v: OccupiedEntry<'a, &'new (), ()>)
-   |                       ^^^^
+LL | fn range_contra_val<'a, 'new>(v: RangeMut<'a, (), &'new ()>) -> RangeMut<'a, (), &'static ()> {
+   |                         ^^^^
    = note: ...does not necessarily outlive the static lifetime
 
 error[E0308]: mismatched types
-  --> $DIR/variance-btree-invariant-types.rs:30:5
+  --> $DIR/variance-btree-invariant-types.rs:31:5
    |
 LL |     v
    |     ^ lifetime mismatch
    |
-   = note: expected struct `std::collections::btree_map::OccupiedEntry<'_, _, &'static ()>`
-              found struct `std::collections::btree_map::OccupiedEntry<'_, _, &'new ()>`
-note: the lifetime `'new` as defined on the function body at 28:23...
-  --> $DIR/variance-btree-invariant-types.rs:28:23
+   = note: expected struct `std::collections::btree_map::OccupiedEntry<'_, &'new (), _>`
+              found struct `std::collections::btree_map::OccupiedEntry<'_, &'static (), _>`
+note: the lifetime `'new` as defined on the function body at 29:20...
+  --> $DIR/variance-btree-invariant-types.rs:29:20
    |
-LL | fn occ_contra_val<'a, 'new>(v: OccupiedEntry<'a, (), &'new ()>)
-   |                       ^^^^
+LL | fn occ_cov_key<'a, 'new>(v: OccupiedEntry<'a, &'static (), ()>)
+   |                    ^^^^
    = note: ...does not necessarily outlive the static lifetime
 
 error[E0308]: mismatched types
@@ -124,12 +139,12 @@ error[E0308]: mismatched types
 LL |     v
    |     ^ lifetime mismatch
    |
-   = note: expected struct `std::collections::btree_map::VacantEntry<'_, &'new (), _>`
-              found struct `std::collections::btree_map::VacantEntry<'_, &'static (), _>`
+   = note: expected struct `std::collections::btree_map::OccupiedEntry<'_, _, &'new ()>`
+              found struct `std::collections::btree_map::OccupiedEntry<'_, _, &'static ()>`
 note: the lifetime `'new` as defined on the function body at 33:20...
   --> $DIR/variance-btree-invariant-types.rs:33:20
    |
-LL | fn vac_cov_key<'a, 'new>(v: VacantEntry<'a, &'static (), ()>)
+LL | fn occ_cov_val<'a, 'new>(v: OccupiedEntry<'a, (), &'static ()>)
    |                    ^^^^
    = note: ...does not necessarily outlive the static lifetime
 
@@ -139,13 +154,13 @@ error[E0308]: mismatched types
 LL |     v
    |     ^ lifetime mismatch
    |
-   = note: expected struct `std::collections::btree_map::VacantEntry<'_, _, &'new ()>`
-              found struct `std::collections::btree_map::VacantEntry<'_, _, &'static ()>`
-note: the lifetime `'new` as defined on the function body at 37:20...
-  --> $DIR/variance-btree-invariant-types.rs:37:20
+   = note: expected struct `std::collections::btree_map::OccupiedEntry<'_, &'static (), _>`
+              found struct `std::collections::btree_map::OccupiedEntry<'_, &'new (), _>`
+note: the lifetime `'new` as defined on the function body at 37:23...
+  --> $DIR/variance-btree-invariant-types.rs:37:23
    |
-LL | fn vac_cov_val<'a, 'new>(v: VacantEntry<'a, (), &'static ()>)
-   |                    ^^^^
+LL | fn occ_contra_key<'a, 'new>(v: OccupiedEntry<'a, &'new (), ()>)
+   |                       ^^^^
    = note: ...does not necessarily outlive the static lifetime
 
 error[E0308]: mismatched types
@@ -154,30 +169,75 @@ error[E0308]: mismatched types
 LL |     v
    |     ^ lifetime mismatch
    |
-   = note: expected struct `std::collections::btree_map::VacantEntry<'_, &'static (), _>`
-              found struct `std::collections::btree_map::VacantEntry<'_, &'new (), _>`
+   = note: expected struct `std::collections::btree_map::OccupiedEntry<'_, _, &'static ()>`
+              found struct `std::collections::btree_map::OccupiedEntry<'_, _, &'new ()>`
 note: the lifetime `'new` as defined on the function body at 41:23...
   --> $DIR/variance-btree-invariant-types.rs:41:23
    |
+LL | fn occ_contra_val<'a, 'new>(v: OccupiedEntry<'a, (), &'new ()>)
+   |                       ^^^^
+   = note: ...does not necessarily outlive the static lifetime
+
+error[E0308]: mismatched types
+  --> $DIR/variance-btree-invariant-types.rs:48:5
+   |
+LL |     v
+   |     ^ lifetime mismatch
+   |
+   = note: expected struct `std::collections::btree_map::VacantEntry<'_, &'new (), _>`
+              found struct `std::collections::btree_map::VacantEntry<'_, &'static (), _>`
+note: the lifetime `'new` as defined on the function body at 46:20...
+  --> $DIR/variance-btree-invariant-types.rs:46:20
+   |
+LL | fn vac_cov_key<'a, 'new>(v: VacantEntry<'a, &'static (), ()>)
+   |                    ^^^^
+   = note: ...does not necessarily outlive the static lifetime
+
+error[E0308]: mismatched types
+  --> $DIR/variance-btree-invariant-types.rs:52:5
+   |
+LL |     v
+   |     ^ lifetime mismatch
+   |
+   = note: expected struct `std::collections::btree_map::VacantEntry<'_, _, &'new ()>`
+              found struct `std::collections::btree_map::VacantEntry<'_, _, &'static ()>`
+note: the lifetime `'new` as defined on the function body at 50:20...
+  --> $DIR/variance-btree-invariant-types.rs:50:20
+   |
+LL | fn vac_cov_val<'a, 'new>(v: VacantEntry<'a, (), &'static ()>)
+   |                    ^^^^
+   = note: ...does not necessarily outlive the static lifetime
+
+error[E0308]: mismatched types
+  --> $DIR/variance-btree-invariant-types.rs:56:5
+   |
+LL |     v
+   |     ^ lifetime mismatch
+   |
+   = note: expected struct `std::collections::btree_map::VacantEntry<'_, &'static (), _>`
+              found struct `std::collections::btree_map::VacantEntry<'_, &'new (), _>`
+note: the lifetime `'new` as defined on the function body at 54:23...
+  --> $DIR/variance-btree-invariant-types.rs:54:23
+   |
 LL | fn vac_contra_key<'a, 'new>(v: VacantEntry<'a, &'new (), ()>)
    |                       ^^^^
    = note: ...does not necessarily outlive the static lifetime
 
 error[E0308]: mismatched types
-  --> $DIR/variance-btree-invariant-types.rs:47:5
+  --> $DIR/variance-btree-invariant-types.rs:60:5
    |
 LL |     v
    |     ^ lifetime mismatch
    |
    = note: expected struct `std::collections::btree_map::VacantEntry<'_, _, &'static ()>`
               found struct `std::collections::btree_map::VacantEntry<'_, _, &'new ()>`
-note: the lifetime `'new` as defined on the function body at 45:23...
-  --> $DIR/variance-btree-invariant-types.rs:45:23
+note: the lifetime `'new` as defined on the function body at 58:23...
+  --> $DIR/variance-btree-invariant-types.rs:58:23
    |
 LL | fn vac_contra_val<'a, 'new>(v: VacantEntry<'a, (), &'new ()>)
    |                       ^^^^
    = note: ...does not necessarily outlive the static lifetime
 
-error: aborting due to 12 previous errors
+error: aborting due to 16 previous errors
 
 For more information about this error, try `rustc --explain E0308`.