From 1975a6e710d6fbb583a415edc3efed1e8970296a Mon Sep 17 00:00:00 2001
From: Albin Hedman <albin9604@gmail.com>
Date: Sat, 26 Dec 2020 01:27:13 +0100
Subject: [PATCH] Constify MaybeUninit::assume_init_read

---
 library/core/src/lib.rs              | 1 +
 library/core/src/mem/maybe_uninit.rs | 3 ++-
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/library/core/src/lib.rs b/library/core/src/lib.rs
index acf4936ee081..4a3020d6b99e 100644
--- a/library/core/src/lib.rs
+++ b/library/core/src/lib.rs
@@ -94,6 +94,7 @@
 #![feature(const_precise_live_drops)]
 #![feature(const_ptr_offset)]
 #![feature(const_ptr_offset_from)]
+#![feature(const_ptr_read)]
 #![feature(const_raw_ptr_comparison)]
 #![feature(const_raw_ptr_deref)]
 #![feature(const_slice_from_raw_parts)]
diff --git a/library/core/src/mem/maybe_uninit.rs b/library/core/src/mem/maybe_uninit.rs
index 57e0bb1499bd..b2a4d897eede 100644
--- a/library/core/src/mem/maybe_uninit.rs
+++ b/library/core/src/mem/maybe_uninit.rs
@@ -575,8 +575,9 @@ pub const fn as_mut_ptr(&mut self) -> *mut T {
     /// // they both get dropped!
     /// ```
     #[unstable(feature = "maybe_uninit_extra", issue = "63567")]
+    #[rustc_const_unstable(feature = "maybe_uninit_extra", issue = "63567")]
     #[inline(always)]
-    pub unsafe fn assume_init_read(&self) -> T {
+    pub const unsafe fn assume_init_read(&self) -> T {
         // SAFETY: the caller must guarantee that `self` is initialized.
         // Reading from `self.as_ptr()` is safe since `self` should be initialized.
         unsafe {