From 9adeb6c49f0c64e33c0d810d48e5612b7ef4d6c3 Mon Sep 17 00:00:00 2001
From: Alexander Medvednikov <alexander@medvednikov.com>
Date: Tue, 21 Apr 2026 05:21:25 +0300
Subject: [PATCH] x.json2: fix @[json_null] field attribute ignored on encode
 (fixes #26905)

---
 vlib/x/json2/encode.v                |  8 +++++++-
 vlib/x/json2/tests/attributes_test.v | 25 +++++++++++++++++++++++++
 2 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/vlib/x/json2/encode.v b/vlib/x/json2/encode.v
index 838909d0e..a82ed111b 100644
--- a/vlib/x/json2/encode.v
+++ b/vlib/x/json2/encode.v
@@ -499,6 +499,7 @@ struct EncoderFieldInfo {
 	is_skip      bool
 	is_omitempty bool
 	is_required  bool
+	is_json_null bool
 }
 
 fn get_value_from_optional[T](val ?T) T {
@@ -557,6 +558,7 @@ fn (mut encoder Encoder) cached_field_infos[T]() []EncoderFieldInfo {
 			mut key_name := ''
 			mut is_omitempty := false
 			mut is_required := false
+			mut is_json_null := false
 			for attr in field.attrs {
 				match attr {
 					'skip' {
@@ -569,6 +571,9 @@ fn (mut encoder Encoder) cached_field_infos[T]() []EncoderFieldInfo {
 					'required' {
 						is_required = true
 					}
+					'json_null' {
+						is_json_null = true
+					}
 					else {}
 				}
 
@@ -586,6 +591,7 @@ fn (mut encoder Encoder) cached_field_infos[T]() []EncoderFieldInfo {
 				is_skip:      is_skip
 				is_omitempty: is_omitempty
 				is_required:  is_required
+				is_json_null: is_json_null
 			}
 		}
 	}
@@ -633,7 +639,7 @@ fn struct_field_should_encode[T](field_info EncoderFieldInfo, val T) bool {
 			return false
 		}
 	}
-	if !field_info.is_required && struct_field_is_none(val) {
+	if !field_info.is_required && !field_info.is_json_null && struct_field_is_none(val) {
 		return false
 	}
 	if struct_field_is_nil(val) {
diff --git a/vlib/x/json2/tests/attributes_test.v b/vlib/x/json2/tests/attributes_test.v
index cc93a220a..e1d37298b 100644
--- a/vlib/x/json2/tests/attributes_test.v
+++ b/vlib/x/json2/tests/attributes_test.v
@@ -46,12 +46,37 @@ struct Foo {
 	a int @[required]
 }
 
+struct JsonNullAttrBar {
+	name ?string @[json_null]
+}
+
+struct JsonNullAttrFoo {
+	name   ?string @[json_null]
+	age    ?int    @[json_null]
+	text   ?string
+	other  ?JsonNullAttrBar
+	other2 ?JsonNullAttrBar @[json_null]
+}
+
 fn test_last_field_requiered() {
 	assert json.decode[Foo]('{"a":0}')! == Foo{
 		a: 0
 	}
 }
 
+fn test_json_null_attribute() {
+	assert json.encode(JsonNullAttrFoo{}) == '{"name":null,"age":null,"other2":null}'
+	assert json.encode(JsonNullAttrFoo{ name: '' }) == '{"name":"","age":null,"other2":null}'
+	assert json.encode(JsonNullAttrFoo{ age: 10 }) == '{"name":null,"age":10,"other2":null}'
+	assert json.encode(JsonNullAttrFoo{
+		age:    10
+		other2: JsonNullAttrBar{
+			name: none
+		}
+	}) == '{"name":null,"age":10,"other2":{"name":null}}'
+	assert json.decode[JsonNullAttrFoo](json.encode(JsonNullAttrFoo{}))! == JsonNullAttrFoo{}
+}
+
 fn test_skip_and_rename_attributes() {
 	assert json.decode[StruWithJsonAttribute]('{"name": "hola1", "a": 2, "b": 3}')! == StruWithJsonAttribute{
 		a:     2
-- 
2.39.5