From 6bac6939e804c55464eaed7cfa047adb4674c267 Mon Sep 17 00:00:00 2001
From: Christopher Durham <cad97@cad97.com>
Date: Sat, 9 Nov 2019 13:43:11 -0500
Subject: [PATCH 1/2] Make Layout::new const

---
 src/libcore/alloc.rs | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/src/libcore/alloc.rs b/src/libcore/alloc.rs
index 71517ffb0065e..b049a446cdcd0 100644
--- a/src/libcore/alloc.rs
+++ b/src/libcore/alloc.rs
@@ -17,7 +17,7 @@ use crate::num::NonZeroUsize;
 #[derive(Debug)]
 pub struct Excess(pub NonNull<u8>, pub usize);
 
-fn size_align<T>() -> (usize, usize) {
+const fn size_align<T>() -> (usize, usize) {
     (mem::size_of::<T>(), mem::align_of::<T>())
 }
 
@@ -119,13 +119,12 @@ impl Layout {
     /// Constructs a `Layout` suitable for holding a value of type `T`.
     #[stable(feature = "alloc_layout", since = "1.28.0")]
     #[inline]
-    pub fn new<T>() -> Self {
+    pub const fn new<T>() -> Self {
         let (size, align) = size_align::<T>();
         // Note that the align is guaranteed by rustc to be a power of two and
         // the size+align combo is guaranteed to fit in our address space. As a
         // result use the unchecked constructor here to avoid inserting code
         // that panics if it isn't optimized well enough.
-        debug_assert!(Layout::from_size_align(size, align).is_ok());
         unsafe {
             Layout::from_size_align_unchecked(size, align)
         }

From 878d3b3171d98f5c68c826d99d30986d60f4f7bb Mon Sep 17 00:00:00 2001
From: CAD97 <cad97@cad97.com>
Date: Tue, 17 Dec 2019 14:55:46 -0500
Subject: [PATCH 2/2] Mark Layout::new as const stable

---
 src/libcore/alloc.rs | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/libcore/alloc.rs b/src/libcore/alloc.rs
index b049a446cdcd0..ceb4a73db61cd 100644
--- a/src/libcore/alloc.rs
+++ b/src/libcore/alloc.rs
@@ -118,6 +118,7 @@ impl Layout {
 
     /// Constructs a `Layout` suitable for holding a value of type `T`.
     #[stable(feature = "alloc_layout", since = "1.28.0")]
+    #[rustc_const_stable(feature = "alloc_layout_const_new", since = "1.42.0")]
     #[inline]
     pub const fn new<T>() -> Self {
         let (size, align) = size_align::<T>();