Auto merge of #78104 - ssomers:btree_root_redux, r=Mark-Simulacrum

BTreeMap: replace Root with NodeRef<Owned, ...>

`NodeRef<marker::Owned, …>` already exists as a representation of root nodes, and it makes more sense to alias `Root` to that than to reuse the space-efficient `BoxedNode` that is oblivious to height, where height is required.

r? `@Mark-Simulacrum`

1 files changed, 2 insertions, 2 deletions

diff --git a/src/test/debuginfo/pretty-std-collections.rs b/src/test/debuginfo/pretty-std-collections.rs
index 1adda813604..8026550882d 100644
--- a/src/test/debuginfo/pretty-std-collections.rs
+++ b/src/test/debuginfo/pretty-std-collections.rs
@@ -102,7 +102,7 @@ fn main() {
         btree_set.insert(i);
     }
 
-    let mut empty_btree_set: BTreeSet<i32> = BTreeSet::new();
+    let empty_btree_set: BTreeSet<i32> = BTreeSet::new();
 
     // BTreeMap
     let mut btree_map = BTreeMap::new();
@@ -110,7 +110,7 @@ fn main() {
         btree_map.insert(i, i);
     }
 
-    let mut empty_btree_map: BTreeMap<i32, u32> = BTreeMap::new();
+    let empty_btree_map: BTreeMap<i32, u32> = BTreeMap::new();
 
     let mut option_btree_map: BTreeMap<bool, Option<bool>> = BTreeMap::new();
     option_btree_map.insert(false, None);