checker: fix error for array of sumtype init (#13501)

vlib/v/checker/containers.v

@@ -71,11 +71,15 @@ pub fn (mut c Checker) array_init(mut node ast.ArrayInit) ast.Type {
 	if node.exprs.len > 0 && node.elem_type == ast.void_type {
 		mut expected_value_type := ast.void_type
 		mut expecting_interface_array := false
+		mut expecting_sumtype_array := false
 		if c.expected_type != 0 {
 			expected_value_type = c.table.value_type(c.expected_type)
-			if c.table.sym(expected_value_type).kind == .interface_ {
+			expected_value_sym := c.table.sym(expected_value_type)
+			if expected_value_sym.kind == .interface_ {
 				// Array of interfaces? (`[dog, cat]`) Save the interface type (`Animal`)
 				expecting_interface_array = true
+			} else if expected_value_sym.kind == .sum_type {
+				expecting_sumtype_array = true
 			}
 		}
 		// expecting_interface_array := c.expected_type != 0 &&
@@ -104,6 +108,11 @@ pub fn (mut c Checker) array_init(mut node ast.ArrayInit) ast.Type {
 					}
 				}
 				continue
+			} else if expecting_sumtype_array {
+				if i == 0 {
+					elem_type = expected_value_type
+				}
+				continue
 			}
 			// The first element's type
 			if i == 0 {

vlib/v/tests/array_of_sumtype_init_test.v

@@ -0,0 +1,25 @@
+pub type MenuItem = Action | Group | Separater
+
+pub struct Group {
+	children []MenuItem
+}
+
+pub struct Separater {}
+
+pub struct Action {}
+
+fn test_array_of_sumtype_init() {
+	g := Group{
+		children: [
+			Action{},
+			Separater{},
+			Group{
+				children: [
+					Action{},
+				]
+			},
+		]
+	}
+	println(g)
+	assert g.children.len == 3
+}