From 717c102f55136653c585a45d6d47fae9a62b2312 Mon Sep 17 00:00:00 2001
From: MSxDOS <15524350+MSxDOS@users.noreply.github.com>
Date: Tue, 16 Jul 2019 21:09:33 +0300
Subject: [PATCH] Update FIELD_OFFSET It may now be used in constants e.g. for
 static assertions (but not inside constant functions, yet, see
 https://github.com/rust-lang/rust/issues/51909)

---
 src/macros.rs | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/src/macros.rs b/src/macros.rs
index 1dff0c2..ace5f94 100644
--- a/src/macros.rs
+++ b/src/macros.rs
@@ -28,7 +28,16 @@ macro_rules! EXTERN {
 macro_rules! FIELD_OFFSET {
     ($_type:ty, $field:ident$(.$cfields:ident)*) => {
         unsafe {
-            &(*$crate::_core::ptr::null::<$_type>()).$field$(.$cfields)* as *const _ as usize
+            union Transmuter<T: 'static> {
+                p: *const T,
+                r: &'static T,
+                i: usize,
+            }
+            Transmuter {
+                r: &(Transmuter {
+                    p: $crate::_core::ptr::null::<$_type>()
+                }.r).$field$(.$cfields)*
+            }.i
         }
     };
 }