cgen,json: bugfix for json.decode; now [skip] fields are initialised

vlib/json/json_decode_test.v

@@ -42,5 +42,30 @@ fn test_decode_u64() ? {
 	data := '{"size": 10737418240}'
 	m := json.decode(Mount, data) ?
 	assert m.size == 10737418240
-	println(m)
+	// println(m)
+}
+
+//
+
+pub struct Comment {
+pub mut:
+	id      string
+	comment string
+}
+
+pub struct Task {
+mut:
+	description    string
+	id             int
+	total_comments int
+	file_name      string    [skip]
+	comments       []Comment [skip]
+}
+
+fn test_skip_fields_should_be_initialised_by_json_decode() ? {
+	data := '{"total_comments": 55, "id": 123}'
+	mut task := json.decode(Task, data) ?
+	assert task.id == 123
+	assert task.total_comments == 55
+	assert task.comments == []
 }

vlib/v/gen/c/json.v

@@ -46,9 +46,15 @@ fn (mut g Gen) gen_jsons() {
 		// Code gen decoder
 		dec_fn_name := js_dec_name(styp)
 		dec_fn_dec := 'Option_$styp ${dec_fn_name}(cJSON* root)'
+
+		init_styp := g.expr_string(ast.Expr(ast.StructInit{
+			typ: utyp
+			typ_str: styp
+		}))
+
 		dec.writeln('
 $dec_fn_dec {
-	$styp res;
+	$styp res = $init_styp;
 	if (!root) {
 		const char *error_ptr = cJSON_GetErrorPtr();
 		if (error_ptr != NULL)	{