From a091a07aa2a70ce45e7c61146b4387630239eae8 Mon Sep 17 00:00:00 2001
From: David Tolnay <dtolnay@gmail.com>
Date: Wed, 25 Oct 2023 19:42:00 -0700
Subject: [PATCH 1/3] Add float NaN tests

---
 test_suite/tests/test_de.rs | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/test_suite/tests/test_de.rs b/test_suite/tests/test_de.rs
index 33dc7351b..b7d82ecff 100644
--- a/test_suite/tests/test_de.rs
+++ b/test_suite/tests/test_de.rs
@@ -11,6 +11,7 @@
 #![cfg_attr(feature = "unstable", feature(never_type))]
 
 use fnv::FnvHasher;
+use serde::de::value::{F32Deserializer, F64Deserializer};
 use serde::de::{Deserialize, DeserializeOwned, Deserializer, IntoDeserializer};
 use serde_derive::Deserialize;
 use serde_test::{assert_de_tokens, Configure, Token};
@@ -832,6 +833,26 @@ fn test_f64() {
     test(1.11, &[Token::F64(1.11)]);
 }
 
+#[test]
+fn test_nan() {
+    let f32_deserializer = F32Deserializer::<serde::de::value::Error>::new;
+    let f64_deserializer = F64Deserializer::<serde::de::value::Error>::new;
+
+    let pos_f32_nan = f32_deserializer(f32::NAN.copysign(1.0));
+    let pos_f64_nan = f64_deserializer(f64::NAN.copysign(1.0));
+    assert!(f32::deserialize(pos_f32_nan).unwrap().is_sign_positive());
+    assert!(f32::deserialize(pos_f64_nan).unwrap().is_sign_positive());
+    assert!(f64::deserialize(pos_f32_nan).unwrap().is_sign_positive());
+    assert!(f64::deserialize(pos_f64_nan).unwrap().is_sign_positive());
+
+    let neg_f32_nan = f32_deserializer(f32::NAN.copysign(-1.0));
+    let neg_f64_nan = f64_deserializer(f64::NAN.copysign(-1.0));
+    assert!(f32::deserialize(neg_f32_nan).unwrap().is_sign_negative());
+    assert!(f32::deserialize(neg_f64_nan).unwrap().is_sign_negative());
+    assert!(f64::deserialize(neg_f32_nan).unwrap().is_sign_negative());
+    assert!(f64::deserialize(neg_f64_nan).unwrap().is_sign_negative());
+}
+
 #[test]
 fn test_char() {
     test('a', &[Token::Char('a')]);

From d2fcc346b9f8f8a61d05474b4e95198788c05ed0 Mon Sep 17 00:00:00 2001
From: David Tolnay <dtolnay@gmail.com>
Date: Wed, 25 Oct 2023 19:37:47 -0700
Subject: [PATCH 2/3] Ensure f32 deserialized from f64 and vice versa preserve
 NaN sign

---
 serde/build.rs        |  6 ++++++
 serde/src/de/impls.rs | 26 ++++++++++++++++++++++++--
 2 files changed, 30 insertions(+), 2 deletions(-)

diff --git a/serde/build.rs b/serde/build.rs
index 2b10c5893..fe5486a7a 100644
--- a/serde/build.rs
+++ b/serde/build.rs
@@ -27,6 +27,12 @@ fn main() {
         println!("cargo:rustc-cfg=no_relaxed_trait_bounds");
     }
 
+    // f32::copysign and f64::copysign stabilized in Rust 1.35.
+    // https://blog.rust-lang.org/2019/05/23/Rust-1.35.0.html#copy-the-sign-of-a-floating-point-number-onto-another
+    if minor < 35 {
+        println!("cargo:rustc-cfg=no_float_copysign");
+    }
+
     // Current minimum supported version of serde_derive crate is Rust 1.56.
     if minor < 56 {
         println!("cargo:rustc-cfg=no_serde_derive");
diff --git a/serde/src/de/impls.rs b/serde/src/de/impls.rs
index fbee1554b..9b8755bd7 100644
--- a/serde/src/de/impls.rs
+++ b/serde/src/de/impls.rs
@@ -180,6 +180,28 @@ macro_rules! num_as_self {
     };
 }
 
+macro_rules! num_as_copysign_self {
+    ($ty:ident : $visit:ident) => {
+        #[inline]
+        fn $visit<E>(self, v: $ty) -> Result<Self::Value, E>
+        where
+            E: Error,
+        {
+            #[cfg(no_float_copysign)]
+            {
+                Ok(v as Self::Value)
+            }
+
+            #[cfg(not(no_float_copysign))]
+            {
+                // Preserve sign of NaN. The `as` produces a nondeterministic sign.
+                let sign = if v.is_sign_positive() { 1.0 } else { -1.0 };
+                Ok((v as Self::Value).copysign(sign))
+            }
+        }
+    };
+}
+
 macro_rules! int_to_int {
     ($ty:ident : $visit:ident) => {
         #[inline]
@@ -351,7 +373,7 @@ impl_deserialize_num! {
 impl_deserialize_num! {
     f32, deserialize_f32
     num_self!(f32:visit_f32);
-    num_as_self!(f64:visit_f64);
+    num_as_copysign_self!(f64:visit_f64);
     num_as_self!(i8:visit_i8 i16:visit_i16 i32:visit_i32 i64:visit_i64);
     num_as_self!(u8:visit_u8 u16:visit_u16 u32:visit_u32 u64:visit_u64);
 }
@@ -359,7 +381,7 @@ impl_deserialize_num! {
 impl_deserialize_num! {
     f64, deserialize_f64
     num_self!(f64:visit_f64);
-    num_as_self!(f32:visit_f32);
+    num_as_copysign_self!(f32:visit_f32);
     num_as_self!(i8:visit_i8 i16:visit_i16 i32:visit_i32 i64:visit_i64);
     num_as_self!(u8:visit_u8 u16:visit_u16 u32:visit_u32 u64:visit_u64);
 }

From 6ba9c12ff6309114fd22d56a9f4acf32284352f4 Mon Sep 17 00:00:00 2001
From: David Tolnay <dtolnay@gmail.com>
Date: Wed, 25 Oct 2023 19:55:12 -0700
Subject: [PATCH 3/3] Float copysign does not exist in libcore yet

---
 serde/src/de/impls.rs | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/serde/src/de/impls.rs b/serde/src/de/impls.rs
index 9b8755bd7..b7e4c549d 100644
--- a/serde/src/de/impls.rs
+++ b/serde/src/de/impls.rs
@@ -187,12 +187,12 @@ macro_rules! num_as_copysign_self {
         where
             E: Error,
         {
-            #[cfg(no_float_copysign)]
+            #[cfg(any(no_float_copysign, not(feature = "std")))]
             {
                 Ok(v as Self::Value)
             }
 
-            #[cfg(not(no_float_copysign))]
+            #[cfg(all(not(no_float_copysign), feature = "std"))]
             {
                 // Preserve sign of NaN. The `as` produces a nondeterministic sign.
                 let sign = if v.is_sign_positive() { 1.0 } else { -1.0 };