Make BTreeMap::new and BTreeSet::new const

3 files changed, 5 insertions, 2 deletions

diff --git a/src/liballoc/collections/btree/map.rs b/src/liballoc/collections/btree/map.rs
index c0b976565e4..bc3411e57c5 100644
--- a/src/liballoc/collections/btree/map.rs
+++ b/src/liballoc/collections/btree/map.rs
@@ -556,7 +556,8 @@ impl<K: Ord, V> BTreeMap<K, V> {
     /// map.insert(1, "a");
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
-    pub fn new() -> BTreeMap<K, V> {
+    #[rustc_const_unstable(feature = "const_btree_new", issue = "71835")]
+    pub const fn new() -> BTreeMap<K, V> {
         BTreeMap { root: None, length: 0 }
     }
 
diff --git a/src/liballoc/collections/btree/set.rs b/src/liballoc/collections/btree/set.rs
index 9bf483f269f..dee5fb878ff 100644
--- a/src/liballoc/collections/btree/set.rs
+++ b/src/liballoc/collections/btree/set.rs
@@ -309,7 +309,8 @@ impl<T: Ord> BTreeSet<T> {
     /// let mut set: BTreeSet<i32> = BTreeSet::new();
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
-    pub fn new() -> BTreeSet<T> {
+    #[rustc_const_unstable(feature = "const_btree_new", issue = "71835")]
+    pub const fn new() -> BTreeSet<T> {
         BTreeSet { map: BTreeMap::new() }
     }
 
diff --git a/src/liballoc/lib.rs b/src/liballoc/lib.rs
index ecec1fb039b..5365c9d0168 100644
--- a/src/liballoc/lib.rs
+++ b/src/liballoc/lib.rs
@@ -82,6 +82,7 @@
 #![feature(cfg_sanitize)]
 #![feature(cfg_target_has_atomic)]
 #![feature(coerce_unsized)]
+#![feature(const_btree_new)]
 #![feature(const_generic_impls_guard)]
 #![feature(const_generics)]
 #![feature(const_in_array_repeat_expressions)]