From f0d2e78d39d0efdb431af0b59c498d532d8146e2 Mon Sep 17 00:00:00 2001
From: Ralf Jung <post@ralfj.de>
Date: Fri, 12 Jun 2020 18:17:30 +0200
Subject: [PATCH 1/2] add raw_ref macros

---
 src/libcore/ptr/mod.rs | 67 ++++++++++++++++++++++++++++++++++++++++++
 src/libstd/lib.rs      |  1 +
 2 files changed, 68 insertions(+)

diff --git a/src/libcore/ptr/mod.rs b/src/libcore/ptr/mod.rs
index 777284ca5c096..199f08c3d5058 100644
--- a/src/libcore/ptr/mod.rs
+++ b/src/libcore/ptr/mod.rs
@@ -1399,3 +1399,70 @@ fnptr_impls_args! { A, B, C, D, E, F, G, H, I }
 fnptr_impls_args! { A, B, C, D, E, F, G, H, I, J }
 fnptr_impls_args! { A, B, C, D, E, F, G, H, I, J, K }
 fnptr_impls_args! { A, B, C, D, E, F, G, H, I, J, K, L }
+
+/// Create a `const` raw pointer to a place, without creating an intermediate reference.
+///
+/// Creating a reference with `&`/`&mut` is only allowed if the pointer is properly aligned
+/// and points to initialized data. For cases where those requirements do not hold,
+/// raw pointers should be used instead. However, `&expr as *const _` creates a reference
+/// before casting it to a raw pointer, and that reference is subject to the same rules
+/// as all other references. This macro can create a raw pointer *without* creating
+/// a reference first.
+///
+/// # Example
+///
+/// ```
+/// #![feature(raw_ref_macros)]
+/// use std::ptr;
+///
+/// #[repr(packed)]
+/// struct Packed {
+///     f1: u8,
+///     f2: u16,
+/// }
+///
+/// let packed = Packed { f1: 1, f2: 2 };
+/// // `&packed.f2` would create an unaligned reference, and thus be Undefined Behavior!
+/// let raw_f2 = ptr::raw_const!(packed.f2);
+/// assert_eq!(unsafe { raw_f2.read_unaligned() }, 2);
+/// ```
+#[unstable(feature = "raw_ref_macros", issue = "none")]
+#[rustc_macro_transparency = "semitransparent"]
+#[allow_internal_unstable(raw_ref_op)]
+pub macro raw_const($e:expr) {
+    &raw const $e
+}
+
+/// Create a `mut` raw pointer to a place, without creating an intermediate reference.
+///
+/// Creating a reference with `&`/`&mut` is only allowed if the pointer is properly aligned
+/// and points to initialized data. For cases where those requirements do not hold,
+/// raw pointers should be used instead. However, `&mut expr as *mut _` creates a reference
+/// before casting it to a raw pointer, and that reference is subject to the same rules
+/// as all other references. This macro can create a raw pointer *without* creating
+/// a reference first.
+///
+/// # Example
+///
+/// ```
+/// #![feature(raw_ref_macros)]
+/// use std::ptr;
+///
+/// #[repr(packed)]
+/// struct Packed {
+///     f1: u8,
+///     f2: u16,
+/// }
+///
+/// let mut packed = Packed { f1: 1, f2: 2 };
+/// // `&mut packed.f2` would create an unaligned reference, and thus be Undefined Behavior!
+/// let raw_f2 = ptr::raw_mut!(packed.f2);
+/// unsafe { raw_f2.write_unaligned(42); }
+/// assert_eq!({packed.f2}, 42); // `{...}` forces copying the field instead of creating a reference.
+/// ```
+#[unstable(feature = "raw_ref_macros", issue = "none")]
+#[rustc_macro_transparency = "semitransparent"]
+#[allow_internal_unstable(raw_ref_op)]
+pub macro raw_mut($e:expr) {
+    &raw mut $e
+}
diff --git a/src/libstd/lib.rs b/src/libstd/lib.rs
index d6493454db591..ef699ede2a140 100644
--- a/src/libstd/lib.rs
+++ b/src/libstd/lib.rs
@@ -298,6 +298,7 @@
 #![feature(prelude_import)]
 #![feature(ptr_internals)]
 #![feature(raw)]
+#![feature(raw_ref_macros)]
 #![feature(renamed_spin_loop)]
 #![feature(rustc_attrs)]
 #![feature(rustc_private)]

From 0265e4e61bcd51b11f0b13b712245feb9c59ab50 Mon Sep 17 00:00:00 2001
From: Ralf Jung <post@ralfj.de>
Date: Tue, 16 Jun 2020 09:25:29 +0200
Subject: [PATCH 2/2] add tracking issue

---
 src/libcore/ptr/mod.rs | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/libcore/ptr/mod.rs b/src/libcore/ptr/mod.rs
index 199f08c3d5058..30c0f9a375714 100644
--- a/src/libcore/ptr/mod.rs
+++ b/src/libcore/ptr/mod.rs
@@ -1426,7 +1426,7 @@ fnptr_impls_args! { A, B, C, D, E, F, G, H, I, J, K, L }
 /// let raw_f2 = ptr::raw_const!(packed.f2);
 /// assert_eq!(unsafe { raw_f2.read_unaligned() }, 2);
 /// ```
-#[unstable(feature = "raw_ref_macros", issue = "none")]
+#[unstable(feature = "raw_ref_macros", issue = "73394")]
 #[rustc_macro_transparency = "semitransparent"]
 #[allow_internal_unstable(raw_ref_op)]
 pub macro raw_const($e:expr) {
@@ -1460,7 +1460,7 @@ pub macro raw_const($e:expr) {
 /// unsafe { raw_f2.write_unaligned(42); }
 /// assert_eq!({packed.f2}, 42); // `{...}` forces copying the field instead of creating a reference.
 /// ```
-#[unstable(feature = "raw_ref_macros", issue = "none")]
+#[unstable(feature = "raw_ref_macros", issue = "73394")]
 #[rustc_macro_transparency = "semitransparent"]
 #[allow_internal_unstable(raw_ref_op)]
 pub macro raw_mut($e:expr) {