tests: cover guarded option sum types in generic calls

vlib/v/tests/generics/generic_option_sumtype_guard_test.v

@@ -0,0 +1,28 @@
+struct Named {
+	name string
+}
+
+struct Empty {}
+
+type Reference = Empty | Named
+
+fn unwrap[T](value ?T) T {
+	return value or { panic('none') }
+}
+
+fn name_after_guard(value ?Reference) string {
+	if value == none {
+		return 'none'
+	}
+	unwrapped := unwrap(value)
+	if unwrapped is Named {
+		return unwrapped.name
+	}
+	return 'empty'
+}
+
+fn test_guarded_optional_sumtype_is_passed_to_generic_option_parameter() {
+	assert name_after_guard(Reference(Named{ name: 'value' })) == 'value'
+	assert name_after_guard(Reference(Empty{})) == 'empty'
+	assert name_after_guard(none) == 'none'
+}