From f3ffcfd61eefe2a4c69ce0f5dcbe819dc7881947 Mon Sep 17 00:00:00 2001
From: Artem Vorotnikov <artem@vorotnikov.me>
Date: Wed, 20 Feb 2019 04:30:53 +0300
Subject: [PATCH 1/2] impl Serialize and Deserialize for core::cmp::Reverse

---
 serde/src/de/impls.rs  |  2 ++
 serde/src/lib.rs       |  1 +
 serde/src/ser/impls.rs | 13 +++++++++++++
 3 files changed, 16 insertions(+)

diff --git a/serde/src/de/impls.rs b/serde/src/de/impls.rs
index 13c8b5a7..9a036180 100644
--- a/serde/src/de/impls.rs
+++ b/serde/src/de/impls.rs
@@ -578,6 +578,8 @@ macro_rules! forwarded_impl {
 #[cfg(all(feature = "std", de_boxed_c_str))]
 forwarded_impl!((), Box<CStr>, CString::into_boxed_c_str);
 
+forwarded_impl!((T), Reverse<T>, Reverse);
+
 ////////////////////////////////////////////////////////////////////////////////
 
 struct OptionVisitor<T> {
diff --git a/serde/src/lib.rs b/serde/src/lib.rs
index 1d953d84..21a8ecd9 100644
--- a/serde/src/lib.rs
+++ b/serde/src/lib.rs
@@ -139,6 +139,7 @@ mod lib {
 
     pub use self::core::cell::{Cell, RefCell};
     pub use self::core::clone::{self, Clone};
+    pub use self::core::cmp::Reverse;
     pub use self::core::convert::{self, From, Into};
     pub use self::core::default::{self, Default};
     pub use self::core::fmt::{self, Debug, Display};
diff --git a/serde/src/ser/impls.rs b/serde/src/ser/impls.rs
index 8b40bda3..a8dd49bf 100644
--- a/serde/src/ser/impls.rs
+++ b/serde/src/ser/impls.rs
@@ -824,3 +824,16 @@ where
         self.0.serialize(serializer)
     }
 }
+
+impl<T> Serialize for Reverse<T>
+    where
+        T: Serialize,
+{
+    #[inline]
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+        where
+            S: Serializer,
+    {
+        self.0.serialize(serializer)
+    }
+}

From 71fe2a55349b8384430417ebc20e05c35c4d69de Mon Sep 17 00:00:00 2001
From: Artem Vorotnikov <artem@vorotnikov.me>
Date: Wed, 20 Feb 2019 04:53:34 +0300
Subject: [PATCH 2/2] Reverse impls available for Rust >=1.19

---
 serde/build.rs         | 6 ++++++
 serde/src/de/impls.rs  | 1 +
 serde/src/lib.rs       | 1 +
 serde/src/ser/impls.rs | 1 +
 4 files changed, 9 insertions(+)

diff --git a/serde/build.rs b/serde/build.rs
index 82129bc7..e27e2f34 100644
--- a/serde/build.rs
+++ b/serde/build.rs
@@ -23,6 +23,12 @@ fn main() {
         println!("cargo:rustc-cfg=collections_bound");
     }
 
+    // core::cmp::Reverse stabilized in Rust 1.19:
+    // https://doc.rust-lang.org/stable/core/cmp/struct.Reverse.html
+    if minor >= 19 {
+        println!("cargo:rustc-cfg=core_reverse");
+    }
+
     // CString::into_boxed_c_str stabilized in Rust 1.20:
     // https://doc.rust-lang.org/std/ffi/struct.CString.html#method.into_boxed_c_str
     if minor >= 20 {
diff --git a/serde/src/de/impls.rs b/serde/src/de/impls.rs
index 9a036180..1c18fd96 100644
--- a/serde/src/de/impls.rs
+++ b/serde/src/de/impls.rs
@@ -578,6 +578,7 @@ macro_rules! forwarded_impl {
 #[cfg(all(feature = "std", de_boxed_c_str))]
 forwarded_impl!((), Box<CStr>, CString::into_boxed_c_str);
 
+#[cfg(core_reverse)]
 forwarded_impl!((T), Reverse<T>, Reverse);
 
 ////////////////////////////////////////////////////////////////////////////////
diff --git a/serde/src/lib.rs b/serde/src/lib.rs
index 21a8ecd9..17d07dc3 100644
--- a/serde/src/lib.rs
+++ b/serde/src/lib.rs
@@ -139,6 +139,7 @@ mod lib {
 
     pub use self::core::cell::{Cell, RefCell};
     pub use self::core::clone::{self, Clone};
+    #[cfg(core_reverse)]
     pub use self::core::cmp::Reverse;
     pub use self::core::convert::{self, From, Into};
     pub use self::core::default::{self, Default};
diff --git a/serde/src/ser/impls.rs b/serde/src/ser/impls.rs
index a8dd49bf..46d406b2 100644
--- a/serde/src/ser/impls.rs
+++ b/serde/src/ser/impls.rs
@@ -825,6 +825,7 @@ where
     }
 }
 
+#[cfg(core_reverse)]
 impl<T> Serialize for Reverse<T>
     where
         T: Serialize,