Implement Ser+De for Saturating<T>

This implementation is heavily inspired by the existing trait
implentation for `std::num::Wrapping<T>`.

fix serde-rs#2708

serde/build.rs

@@ -64,6 +64,12 @@ fn main() {
     if minor < 64 {
         println!("cargo:rustc-cfg=no_core_cstr");
     }
+
+    // Support for core::num::Saturating and std::num::Saturating stabilized in Rust 1.74
+    // https://blog.rust-lang.org/2023/11/16/Rust-1.74.0.html#stabilized-apis
+    if minor < 74 {
+        println!("cargo:rustc-cfg=no_core_num_saturating");
+    }
 }
 
 fn rustc_minor_version() -> Option<u32> {

serde/src/de/impls.rs

@@ -3004,6 +3004,19 @@ where
     }
 }
 
+#[cfg(not(no_core_num_saturating))]
+impl<'de, T> Deserialize<'de> for Saturating<T>
+where
+    T: Deserialize<'de>,
+{
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        Deserialize::deserialize(deserializer).map(Saturating)
+    }
+}
+
 #[cfg(all(feature = "std", not(no_std_atomic)))]
 macro_rules! atomic_impl {
     ($($ty:ident $size:expr)*) => {

serde/src/lib.rs

@@ -274,6 +274,9 @@ mod lib {
     pub use std::sync::atomic::{AtomicI64, AtomicU64};
     #[cfg(all(feature = "std", not(no_target_has_atomic), target_has_atomic = "ptr"))]
     pub use std::sync::atomic::{AtomicIsize, AtomicUsize};
+
+    #[cfg(not(no_core_num_saturating))]
+    pub use self::core::num::Saturating;
 }
 
 // None of this crate's error handling needs the `From::from` error conversion

serde/src/ser/impls.rs

@@ -1026,6 +1026,20 @@ where
     }
 }
 
+#[cfg(not(no_core_num_saturating))]
+impl<T> Serialize for Saturating<T>
+where
+    T: Serialize,
+{
+    #[inline]
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        self.0.serialize(serializer)
+    }
+}
+
 impl<T> Serialize for Reverse<T>
 where
     T: Serialize,