cgen: fix option struct init with reference option (#17617)

vlib/v/gen/c/struct.v

@@ -547,10 +547,11 @@ fn (mut g Gen) struct_init_field(sfield ast.StructInitField, language ast.Langua
 				g.write('/* autoref */&')
 			}
 
-			if sfield.expected_type.has_flag(.option)
+			if (sfield.expected_type.has_flag(.option) && !sfield.typ.has_flag(.option))
 				|| (sfield.expected_type.has_flag(.result) && !sfield.typ.has_flag(.result)) {
 				g.expr_with_opt(sfield.expr, sfield.typ, sfield.expected_type)
 			} else {
+				g.left_is_opt = true
 				g.expr_with_cast(sfield.expr, sfield.typ, sfield.expected_type)
 			}
 		}

vlib/v/tests/option_struct_init_with_ref_opt_test.v

@@ -0,0 +1,51 @@
+struct Node {
+	value int
+mut:
+	prev ?&Node = none
+	next ?&Node = none
+}
+
+struct LinkedList {
+mut:
+	head ?&Node = none
+	tail ?&Node = none
+}
+
+pub fn (mut l LinkedList) push(value int) {
+	node := &Node{
+		value: value
+		prev: l.tail
+	}
+	if l.head == none {
+		l.head = node
+	} else {
+		mut tail := l.tail or { panic('head is not none but tail is') }
+		tail.next = node
+	}
+	l.tail = node
+}
+
+pub fn (mut l LinkedList) pop() int {
+	tail := l.tail or { panic('Empty list not supported') }
+	if tail.prev == none { // single element
+		l.head = none
+		l.tail = none
+	} else { // multiple elements
+		mut prev := tail.prev or { panic('prev cannot be none at this point') }
+		prev.next = none
+		l.tail = prev
+	}
+	return tail.value
+}
+
+fn test_option_struct_init_with_ref_opt() {
+	mut ll := LinkedList{}
+	ll.push(11)
+	ll.push(22)
+	ret1 := ll.pop()
+	println(ret1)
+	assert ret1 == 22
+	ret2 := ll.pop()
+	println(ret2)
+	assert ret2 == 11
+}