From 8bab6a37a4c999abc2a4f6898f1e258dd7941aa5 Mon Sep 17 00:00:00 2001
From: Birh Burh <birhburh@gmail.com>
Date: Sat, 31 Aug 2024 17:11:04 +0200
Subject: [PATCH] serde_json: serialize None as null if there is default
 attribute

---
 derive/src/serde_json.rs | 30 +++++++++++++++++++++++++++---
 tests/json.rs            | 16 ++++++++++++----
 2 files changed, 39 insertions(+), 7 deletions(-)

diff --git a/derive/src/serde_json.rs b/derive/src/serde_json.rs
index 0bedcd4..aae2387 100644
--- a/derive/src/serde_json.rs
+++ b/derive/src/serde_json.rs
@@ -57,16 +57,40 @@ pub fn derive_ser_json_struct(struct_: &Struct) -> TokenStream {
             let proxied_field = ser_proxy_guard(&format!("self.{struct_fieldname}"), field);
 
             if field.ty.base() == "Option" {
+                let proxy_attr = crate::shared::attrs_proxy(&field.attributes);
+                let null_on_none = proxy_attr.is_none();
+                let field_header = &format!("if first_field_was_serialized {{
+                                                 s.conl();
+                                             }};
+                                             first_field_was_serialized = true;
+                                             s.field(d+1, \"{}\");", json_fieldname);
                 l!(
                     s,
-                    "if let Some(t) = &{} {{ if first_field_was_serialized {{ s.conl(); }};first_field_was_serialized = true;s.field(d+1, \"{}\");t.ser_json(d+1, s);}};",
+                    "{}
+                    if let Some(t) = &{} {{
+                        {}
+                        t.ser_json(d+1, s);
+                    }} {}",
+                    if null_on_none { field_header } else { "" },
                     proxied_field,
-                    json_fieldname
+                    if null_on_none { "" } else { field_header },
+                    if null_on_none {
+                        "else {{
+                            Option::<i32>::ser_json(&None, d+1, s);
+                        }}"
+                    } else {
+                        ""
+                    }
                 );
             } else {
                 l!(
                     s,
-                    "if first_field_was_serialized {{ s.conl(); }};first_field_was_serialized = true;s.field(d+1,\"{}\"); {}.ser_json(d+1, s);",
+                    "if first_field_was_serialized {{
+                        s.conl();
+                    }};
+                    first_field_was_serialized = true;
+                    s.field(d+1,\"{}\");
+                    {}.ser_json(d+1, s);",
                     json_fieldname,
                     proxied_field
                 );
diff --git a/tests/json.rs b/tests/json.rs
index d8b0bc8..542f040 100644
--- a/tests/json.rs
+++ b/tests/json.rs
@@ -271,8 +271,8 @@ fn rename() {
 }
 
 #[test]
-fn de_field_default() {
-    #[derive(DeJson)]
+fn de_ser_field_default() {
+    #[derive(DeJson, SerJson)]
     struct Foo {
         x: i32,
     }
@@ -282,7 +282,7 @@ fn de_field_default() {
         }
     }
 
-    #[derive(DeJson)]
+    #[derive(DeJson, SerJson)]
     pub struct Test {
         a: i32,
         #[nserde(default)]
@@ -302,6 +302,8 @@ fn de_field_default() {
         g: Option<i32>,
         #[nserde(default = "world")]
         h: Option<String>,
+        #[nserde(default = 5.2)]
+        i: Option<f32>,
     }
 
     fn some_value() -> f32 {
@@ -310,7 +312,8 @@ fn de_field_default() {
 
     let json = r#"{
         "a": 1,
-        "foo2": { "x": 3 }
+        "foo2": { "x": 3 },
+        "i": null
     }"#;
 
     let test: Test = DeJson::deserialize_json(json).unwrap();
@@ -324,6 +327,11 @@ fn de_field_default() {
     assert_eq!(test.h, Some(String::from("world")));
     assert_eq!(test.foo.x, 23);
     assert_eq!(test.foo2.x, 3);
+    assert_eq!(test.i, None);
+
+    let ser_json = r#"{"a":1,"foo":{"x":23},"foo2":{"x":3},"b":4.0,"c":3.0,"d":1,"e":"hello","f":{"x":3},"g":5,"h":"world","i":null}"#;
+    let serialized = SerJson::serialize_json(&test);
+    assert_eq!(serialized, ser_json);
 }
 
 #[test]