From d22b755310833c0a85dc7a9fed2f370e8162aaf4 Mon Sep 17 00:00:00 2001
From: Mads Marquart <mads@marquart.dk>
Date: Tue, 1 Jun 2021 16:43:53 +0200
Subject: [PATCH 1/2] Use a struct to represent Exception instead of an
 uninhabited enum

Having pointers to uninhabited enums is maybe undefined behaviour, and dereferencing them definitely is.
---
 objc_exception/src/lib.rs | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/objc_exception/src/lib.rs b/objc_exception/src/lib.rs
index 80098a24f..df924e3b9 100644
--- a/objc_exception/src/lib.rs
+++ b/objc_exception/src/lib.rs
@@ -24,7 +24,18 @@ extern "C" {
 }
 
 /// An opaque type representing any Objective-C object thrown as an exception.
-pub enum Exception {}
+///
+/// In the future this will be an [`extern type`][rfc-1861], if that gets
+/// stabilized.
+///
+/// [rfc-1861]: https://rust-lang.github.io/rfcs/1861-extern-types.html
+#[repr(C)]
+pub struct Exception {
+    /// See the [Nomicon] for details on representing opaque structs.
+    ///
+    /// [Nomicon]: https://doc.rust-lang.org/nomicon/ffi.html#representing-opaque-structs
+    _priv: [u8; 0],
+}
 
 /// Throws an Objective-C exception.
 /// The argument must be a pointer to an Objective-C object.

From cc1430af276a80c03a11bbe916fdee303ebdd037 Mon Sep 17 00:00:00 2001
From: Mads Marquart <mads@marquart.dk>
Date: Tue, 31 Aug 2021 18:07:29 +0200
Subject: [PATCH 2/2] Fix opaque struct usage in objc_foundation

---
 examples/foundation_custom_class.rs | 10 +++++++++-
 objc_foundation/src/macros.rs       |  4 +++-
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/examples/foundation_custom_class.rs b/examples/foundation_custom_class.rs
index 22bef447b..30dee30bd 100644
--- a/examples/foundation_custom_class.rs
+++ b/examples/foundation_custom_class.rs
@@ -6,7 +6,15 @@ use objc::runtime::{Class, Object, Sel};
 use objc::Message;
 use objc_foundation::{INSObject, NSObject};
 
-pub enum MYObject {}
+/// In the future this should be an `extern type`, if that gets stabilized,
+/// see [RFC-1861](https://rust-lang.github.io/rfcs/1861-extern-types.html).
+#[repr(C)]
+pub struct MYObject {
+    /// See the [Nomicon] for details on representing opaque structs.
+    ///
+    /// [Nomicon]: https://doc.rust-lang.org/nomicon/ffi.html#representing-opaque-structs
+    _priv: [u8; 0],
+}
 
 impl MYObject {
     fn number(&self) -> u32 {
diff --git a/objc_foundation/src/macros.rs b/objc_foundation/src/macros.rs
index 9b45930af..4c2e39a5d 100644
--- a/objc_foundation/src/macros.rs
+++ b/objc_foundation/src/macros.rs
@@ -1,8 +1,10 @@
 #[macro_export]
 macro_rules! object_struct {
     ($name:ident) => {
+        // TODO: `extern type`
+        #[repr(C)]
         pub struct $name {
-            _private: (),
+            _private: [u8; 0],
         }
 
         unsafe impl ::objc::Message for $name {}