json: fix raw decode to option string of complex data (#18902)

vlib/json/json_option_raw_test.v

@@ -0,0 +1,62 @@
+import json
+
+pub struct Dto {
+pub:
+	key      string  [raw]
+	key2     string  [raw]
+	data     ?string [raw]
+	optional ?string [raw]
+}
+
+fn test_main() {
+	raw_json := '{
+        "key": [1, 2, "test"],
+        "key2": { "test": 1 },
+        "data": { "test": 1 },
+        "optional": "test"
+    }'
+
+	dto := json.decode(Dto, raw_json)!
+
+	println(dto)
+	assert dto.data? == '{"test":1}'
+}
+
+fn test_none() {
+	raw_json := '{
+        "key": [1, 2, "test"],
+        "optional": "test"
+    }'
+
+	dto := json.decode(Dto, raw_json)!
+
+	println(dto)
+	assert dto.data == none
+	assert dto.optional? == '"test"'
+}
+
+fn test_null() {
+	raw_json := '{
+        "key": [1, 2, "test"],
+       	"key2": null,
+        "data": null,
+        "optional": "test"
+    }'
+
+	dto := json.decode(Dto, raw_json)!
+
+	println(dto)
+	assert dto.key2 == 'null'
+	assert dto.data? == 'null'
+}
+
+fn test_not_set() {
+	raw_json := '{
+    }'
+
+	dto := json.decode(Dto, raw_json)!
+
+	println(dto)
+	assert dto.data == none
+	assert dto.optional == none
+}

vlib/v/gen/c/json.v

@@ -629,7 +629,7 @@ fn (mut g Gen) gen_struct_enc_dec(utyp ast.Type, type_info ast.TypeInfo, styp st
 			if field.typ.has_flag(.option) {
 				g.gen_json_for_type(field.typ)
 				base_typ := g.base_type(field.typ)
-				dec.writeln('\tif (!cJSON_IsString(js_get(root, "${name}")))')
+				dec.writeln('\tif (js_get(root, "${name}") == NULL)')
 				dec.writeln('\t\t_option_none(&(${base_typ}[]) { {0} }, &${prefix}${op}${c_name(field.name)}, sizeof(${base_typ}));')
 				dec.writeln('\telse')
 				dec.writeln('\t\t_option_ok(&(${base_typ}[]) {  tos5(cJSON_PrintUnformatted(js_get(root, "${name}"))) }, &${prefix}${op}${c_name(field.name)}, sizeof(${base_typ}));')