ast: fix array of reference sumtype appending (#14797)

vlib/v/ast/table.v

@@ -1342,7 +1342,7 @@ pub fn (t &Table) is_sumtype_or_in_variant(parent Type, typ Type) bool {
 	if typ == 0 {
 		return false
 	}
-	if t.type_kind(typ) == .sum_type && parent.idx() == typ.idx()
+	if t.sym(typ).kind == .sum_type && parent.idx() == typ.idx()
 		&& parent.nr_muls() == typ.nr_muls() {
 		return true
 	}

vlib/v/tests/array_of_reference_sumtype_append_test.v

@@ -0,0 +1,35 @@
+struct Element {
+	AbstractNode
+	name       string
+	attributes []&Attribute
+}
+
+struct Attribute {
+	AbstractNode
+	name  string
+	value string
+}
+
+pub type Node = Attribute | Element
+
+struct AbstractNode {
+pub mut:
+	child_nodes []&Node
+}
+
+pub fn (mut n AbstractNode) append_child(child &Node) {
+	n.child_nodes << child
+}
+
+fn test_array_of_reference_sumtype_append() {
+	mut parent := &Element{
+		name: 'parent'
+	}
+	mut child := &Element{
+		name: 'child'
+	}
+	parent.append_child(child)
+
+	dump(parent)
+	assert parent.child_nodes[0].name == 'child'
+}