From af8d110201aaf6e5846f146b73207f7887327638 Mon Sep 17 00:00:00 2001
From: zachs18 <8355914+zachs18@users.noreply.github.com>
Date: Thu, 31 Oct 2024 05:30:11 +0000
Subject: [PATCH] More `TransparentWrapper` impls (`core::cmp::Reverse` and
 `core::num::Saturating`) (#269)

* impl<T> TransparentWrapper<T> for core::cmp::Reverse<T>

* impl<T> TransparentWrapper<T> for core::num::Saturating<T>, with a new feature for non-base-MSRV stdlib TransparentWrapper impls.

* Restrict TransparentWrapper<T> for Reverse<T> to cfg(feature = "transparentwrapper_extra").

* nightly_docs for transparent_wrapper_extra

---------

Co-authored-by: Lokathor <zefria@gmail.com>
---
 Cargo.toml         |  5 +++++
 src/transparent.rs | 17 +++++++++++++++++
 2 files changed, 22 insertions(+)

diff --git a/Cargo.toml b/Cargo.toml
index 67ff212..ee1ccca 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -40,6 +40,11 @@ aarch64_simd = [] # MSRV 1.59.0: support aarch64 simd types
 
 must_cast = [] # MSRV 1.64.0: support the `must` module.
 
+# Adds `TransparentWrapper` impls for stdlib types newer than bytemuck's base MSRV.
+# Current MSRV 1.74.0: `core::num::Saturating`.
+# MSRV may increase if impls are added for newer types.
+transparentwrapper_extra = []
+
 const_zeroed = [] # MSRV 1.75.0: support const `zeroed()`
 
 # Do not use if you can avoid it, because this is **unsound**!!!!
diff --git a/src/transparent.rs b/src/transparent.rs
index 44f2606..a588eea 100644
--- a/src/transparent.rs
+++ b/src/transparent.rs
@@ -303,3 +303,20 @@ pub unsafe trait TransparentWrapper<Inner: ?Sized> {
 }
 
 unsafe impl<T> TransparentWrapper<T> for core::num::Wrapping<T> {}
+#[cfg(feature = "transparentwrapper_extra")]
+#[cfg_attr(
+  feature = "nightly_docs",
+  doc(cfg(feature = "transparentwrapper_extra"))
+)]
+unsafe impl<T> TransparentWrapper<T> for core::num::Saturating<T> {}
+
+// Note that `Reverse` existed since Rust 1.19.0, but was only made `#[repr(transparent)]`
+// in Rust 1.52.0 (PR: https://github.com/rust-lang/rust/pull/81879), so we have it under
+// the same feature as `Saturating`, which was stabilized in Rust 1.74.0, so that this
+// impl cannot be used on a version before 1.52.0 where it would be unsound.
+#[cfg(feature = "transparentwrapper_extra")]
+#[cfg_attr(
+  feature = "nightly_docs",
+  doc(cfg(feature = "transparentwrapper_extra"))
+)]
+unsafe impl<T> TransparentWrapper<T> for core::cmp::Reverse<T> {}