support additional experimental typechecker options

Author: fredemmott

.hhconfig

@@ -1,7 +1,8 @@
 assume_php=false
-enable_experimental_tc_features = no_fallback_in_namespaces
+enable_experimental_tc_features = no_fallback_in_namespaces, unpacking_check_arity, disallow_refs_in_array, disallow_untyped_lambda_as_non_function_type
 safe_array = true
 safe_vector_array = true
+disallow_destruct = true
 
 # ignore HHAST as:
 # - otherwise, we get a circular dependency

composer.lock

@@ -204,8 +204,8 @@ function coalesce<T>(?T $_head, ?T ...$rest): ?T {
  *
  * Will take `?T ...$args` when HHVM 3.12 support is dropped.
  */
-function coalescex<T>(?T $_head, ?T ...$_rest): T {
-  $result = coalesce(...\func_get_args());
+function coalescex<T>(?T $head, ?T ...$rest): T {
+  $result = coalesce($head, ...$rest);
   invariant($result !== null, 'All arguments were null');
   return $result;
 }