From 8cdb507bedad05bc516c470c6f8245a67023f8f9 Mon Sep 17 00:00:00 2001
From: Felipe Pena <felipensp@gmail.com>
Date: Mon, 30 Dec 2024 15:59:28 -0300
Subject: [PATCH] json: support `@[json_null]` tag to enforce `null`, when
 encoding `none` option values (#23319)

---
 vlib/json/tests/json_is_null_attr_test.v | 26 ++++++++++++++++++++++++
 vlib/v/gen/c/json.v                      | 10 ++++++++-
 2 files changed, 35 insertions(+), 1 deletion(-)
 create mode 100644 vlib/json/tests/json_is_null_attr_test.v

diff --git a/vlib/json/tests/json_is_null_attr_test.v b/vlib/json/tests/json_is_null_attr_test.v
new file mode 100644
index 0000000000..98abc96674
--- /dev/null
+++ b/vlib/json/tests/json_is_null_attr_test.v
@@ -0,0 +1,26 @@
+import json
+
+struct Bar {
+	name ?string @[json_null]
+}
+
+struct Foo {
+	name   ?string @[json_null]
+	age    ?int    @[json_null]
+	text   ?string
+	other  ?Bar
+	other2 ?Bar @[json_null]
+}
+
+fn test_main() {
+	assert json.encode(Foo{}) == '{"name":null,"age":null,"other2":null}'
+	assert json.encode(Foo{ name: '' }) == '{"name":"","age":null,"other2":null}'
+	assert json.encode(Foo{ age: 10 }) == '{"name":null,"age":10,"other2":null}'
+	assert json.encode(Foo{
+		age:    10
+		other2: Bar{
+			name: none
+		}
+	}) == '{"name":null,"age":10,"other2":{"name":null}}'
+	assert json.decode(Foo, json.encode(Foo{}))! == Foo{}
+}
diff --git a/vlib/v/gen/c/json.v b/vlib/v/gen/c/json.v
index 2013abb461..e379385945 100644
--- a/vlib/v/gen/c/json.v
+++ b/vlib/v/gen/c/json.v
@@ -649,6 +649,7 @@ fn (mut g Gen) gen_struct_enc_dec(utyp ast.Type, type_info ast.TypeInfo, styp st
 		mut is_required := false
 		mut is_omit_empty := false
 		mut skip_embed := false
+		mut is_json_null := false
 
 		for attr in field.attrs {
 			match attr.name {
@@ -672,6 +673,9 @@ fn (mut g Gen) gen_struct_enc_dec(utyp ast.Type, type_info ast.TypeInfo, styp st
 				'omitempty' {
 					is_omit_empty = true
 				}
+				'json_null' {
+					is_json_null = true
+				}
 				else {}
 			}
 		}
@@ -952,7 +956,11 @@ fn (mut g Gen) gen_struct_enc_dec(utyp ast.Type, type_info ast.TypeInfo, styp st
 		}
 
 		if is_option {
-			enc.writeln('\t} // !none')
+			if is_json_null {
+				enc.writeln('\t} else {')
+				enc.writeln('\t\tcJSON_AddItemToObject(o, "${name}", cJSON_CreateNull());')
+			}
+			enc.writeln('\t}')
 		}
 	}
 }