From fd6548ee0cf94d1629e616d78ab99c2b374abe37 Mon Sep 17 00:00:00 2001
From: Peter Todd <pete@petertodd.org>
Date: Mon, 15 Feb 2021 02:36:48 -0500
Subject: [PATCH] Implement `Allocator` for `!`

Useful to represent situations where something will never actually
allocate, such as immutable version of a copy-on-write type.
---
 library/core/src/alloc/mod.rs | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/library/core/src/alloc/mod.rs b/library/core/src/alloc/mod.rs
index 06a761531b676..4946d140d4cc6 100644
--- a/library/core/src/alloc/mod.rs
+++ b/library/core/src/alloc/mod.rs
@@ -404,3 +404,16 @@ where
         unsafe { (**self).shrink(ptr, old_layout, new_layout) }
     }
 }
+
+#[unstable(feature = "allocator_api", issue = "32838")]
+unsafe impl Allocator for ! {
+    #[inline]
+    fn allocate(&self, _: Layout) -> Result<NonNull<[u8]>, AllocError> {
+        *self
+    }
+
+    #[inline]
+    unsafe fn deallocate(&self, _: NonNull<u8>, _: Layout) {
+        *self
+    }
+}