From 346a49fe48fd22bd9588d929bc3115016e654801 Mon Sep 17 00:00:00 2001
From: Nixon Enraght-Moony <nixon.emoony@gmail.com>
Date: Sun, 2 Oct 2022 12:57:10 +0100
Subject: [PATCH] Make Hash{Set,Map}::with_hasher unstably const

---
 library/std/src/collections/hash/map.rs       | 3 ++-
 library/std/src/collections/hash/map/tests.rs | 6 ++++++
 library/std/src/collections/hash/set.rs       | 3 ++-
 library/std/src/collections/hash/set/tests.rs | 6 ++++++
 library/std/src/lib.rs                        | 1 +
 5 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/library/std/src/collections/hash/map.rs b/library/std/src/collections/hash/map.rs
index d2db4bb7a46f5..34983b976e3e6 100644
--- a/library/std/src/collections/hash/map.rs
+++ b/library/std/src/collections/hash/map.rs
@@ -280,7 +280,8 @@ impl<K, V, S> HashMap<K, V, S> {
     /// ```
     #[inline]
     #[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
-    pub fn with_hasher(hash_builder: S) -> HashMap<K, V, S> {
+    #[rustc_const_unstable(feature = "const_collections_with_hasher", issue = "102575")]
+    pub const fn with_hasher(hash_builder: S) -> HashMap<K, V, S> {
         HashMap { base: base::HashMap::with_hasher(hash_builder) }
     }
 
diff --git a/library/std/src/collections/hash/map/tests.rs b/library/std/src/collections/hash/map/tests.rs
index cb3032719fa64..65634f2063f36 100644
--- a/library/std/src/collections/hash/map/tests.rs
+++ b/library/std/src/collections/hash/map/tests.rs
@@ -1115,3 +1115,9 @@ fn from_array() {
     // that's a problem!
     let _must_not_require_type_annotation = HashMap::from([(1, 2)]);
 }
+
+#[test]
+fn const_with_hasher() {
+    const X: HashMap<(), (), ()> = HashMap::with_hasher(());
+    assert_eq!(X.len(), 0);
+}
diff --git a/library/std/src/collections/hash/set.rs b/library/std/src/collections/hash/set.rs
index 5b6a415fadc1e..c36eeae3388db 100644
--- a/library/std/src/collections/hash/set.rs
+++ b/library/std/src/collections/hash/set.rs
@@ -376,7 +376,8 @@ impl<T, S> HashSet<T, S> {
     /// ```
     #[inline]
     #[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
-    pub fn with_hasher(hasher: S) -> HashSet<T, S> {
+    #[rustc_const_unstable(feature = "const_collections_with_hasher", issue = "102575")]
+    pub const fn with_hasher(hasher: S) -> HashSet<T, S> {
         HashSet { base: base::HashSet::with_hasher(hasher) }
     }
 
diff --git a/library/std/src/collections/hash/set/tests.rs b/library/std/src/collections/hash/set/tests.rs
index 233db276b9e61..941a0450cc770 100644
--- a/library/std/src/collections/hash/set/tests.rs
+++ b/library/std/src/collections/hash/set/tests.rs
@@ -496,3 +496,9 @@ fn from_array() {
     // that's a problem!
     let _must_not_require_type_annotation = HashSet::from([1, 2]);
 }
+
+#[test]
+fn const_with_hasher() {
+    const X: HashSet<(), ()> = HashSet::with_hasher(());
+    assert_eq!(X.len(), 0);
+}
diff --git a/library/std/src/lib.rs b/library/std/src/lib.rs
index 97eed8a65c52e..353785d3d12a0 100644
--- a/library/std/src/lib.rs
+++ b/library/std/src/lib.rs
@@ -351,6 +351,7 @@
 // Only used in tests/benchmarks:
 //
 // Only for const-ness:
+#![feature(const_collections_with_hasher)]
 #![feature(const_io_structs)]
 #![feature(const_ip)]
 #![feature(const_ipv4)]