From 358027748bbc883d91efbc88cc1118526539acba Mon Sep 17 00:00:00 2001
From: Alexander Medvednikov <alexander@medvednikov.com>
Date: Thu, 26 Feb 2026 10:23:15 +0300
Subject: [PATCH] json: fix decode transforms empty objects to empty strings
 (fixes #19791)

---
 vlib/json/json_primitives.c.v                    | 12 +++++++++---
 vlib/json/tests/json_prim_type_validation_test.v | 13 +++++++++++++
 vlib/v/gen/c/json.v                              |  2 +-
 3 files changed, 23 insertions(+), 4 deletions(-)

diff --git a/vlib/json/json_primitives.c.v b/vlib/json/json_primitives.c.v
index 97fec6cd5..081fd37be 100644
--- a/vlib/json/json_primitives.c.v
+++ b/vlib/json/json_primitives.c.v
@@ -24,6 +24,8 @@ pub struct C.cJSON {
 }
 
 fn C.cJSON_IsTrue(&C.cJSON) bool
+fn C.cJSON_IsObject(&C.cJSON) bool
+fn C.cJSON_IsArray(&C.cJSON) bool
 
 fn C.cJSON_CreateNumber(f64) &C.cJSON
 
@@ -163,10 +165,14 @@ fn decode_string(root &C.cJSON) string {
 	if isnil(root) {
 		return ''
 	}
-	if isnil(root.valuestring) {
-		return ''
+	if !isnil(root.valuestring) {
+		return unsafe { tos_clone(&u8(root.valuestring)) } // , _strlen(root.valuestring))
 	}
-	return unsafe { tos_clone(&u8(root.valuestring)) } // , _strlen(root.valuestring))
+	// Object/array values can be stringified JSON payloads (e.g. `{}` from JSON.stringify()).
+	if C.cJSON_IsObject(root) || C.cJSON_IsArray(root) {
+		return json_print(root)
+	}
+	return ''
 }
 
 @[markused]
diff --git a/vlib/json/tests/json_prim_type_validation_test.v b/vlib/json/tests/json_prim_type_validation_test.v
index 3477ff0f1..b426a709f 100644
--- a/vlib/json/tests/json_prim_type_validation_test.v
+++ b/vlib/json/tests/json_prim_type_validation_test.v
@@ -8,6 +8,11 @@ struct MyStruct {
 	active bool
 }
 
+struct TestStructOne {
+	property_one string @[json: 'propertyOne']
+	property_two string @[json: 'propertyTwo']
+}
+
 fn test_main() {
 	mut errors := 0
 	json.decode(MyStruct, '{ "name": 1}') or {
@@ -24,4 +29,12 @@ fn test_main() {
 	}
 	res := json.decode(MyStruct, '{ "name": "John Doe", "age": "1"}') or { panic(err) }
 	assert errors == 3
+	assert res.name == 'John Doe'
+}
+
+fn test_decode_object_into_string_field() {
+	payload := '{"propertyOne":"property_two should stay a regular string {}","propertyTwo":{}}'
+	res := json.decode(TestStructOne, payload) or { panic(err) }
+	assert res.property_one == 'property_two should stay a regular string {}'
+	assert res.property_two == '{}'
 }
diff --git a/vlib/v/gen/c/json.v b/vlib/v/gen/c/json.v
index f781a3d0f..d5c010280 100644
--- a/vlib/v/gen/c/json.v
+++ b/vlib/v/gen/c/json.v
@@ -645,7 +645,7 @@ fn (mut g Gen) gen_prim_type_validation(name string, typ ast.Type, tmp string, i
 	type_check := if typ.is_int() || typ.is_float() {
 		'${none_check}cJSON_IsNumber(jsonroot_${tmp}) || (cJSON_IsString(jsonroot_${tmp}) && strlen(jsonroot_${tmp}->valuestring))'
 	} else if typ.is_string() {
-		'${none_check}cJSON_IsString(jsonroot_${tmp})'
+		'${none_check}(cJSON_IsString(jsonroot_${tmp}) || cJSON_IsObject(jsonroot_${tmp}) || cJSON_IsArray(jsonroot_${tmp}))'
 	} else if typ.is_bool() {
 		'${none_check}cJSON_IsBool(jsonroot_${tmp})'
 	} else {
-- 
2.39.5