system: use is_int()/array_key_first() in toArray() and fromArray() #9485

The approximation of the magic here is that we are looking for array
elements created by a natural append [] = or equivalent which has
an integer key of a rough range of 0 to count() - 1, but not always as
we can see from the ticket.

unset() breaks the pledge of sequential lists and makes array_is_list()
fail.  Sorting would also break the sequential pledge without resetting
the keyes using array_values() but that approach is too broad.

Instead, get a single key we can do a strict int type check on so that
we are as likely to succeed as was the case before the change in 7ee3b2c.

It's also fast.  ;)

Author: fichtner

src/opnsense/mvc/app/library/OPNsense/Core/Config.php

@@ -118,7 +118,7 @@ public function toArray($forceList = null, $node = null)
                     $old_content = $result[$xmlNodeName];
                     // check if array content is associative, move items to new list
                     // (handles first item of specific type)
-                    if (!is_array($old_content) || !array_is_list($old_content)) {
+                    if (!is_array($old_content) || !is_int(array_key_first($old_content))) {
                         $result[$xmlNodeName] = array();
                         $result[$xmlNodeName][] = $old_content;
                     }
@@ -240,10 +240,10 @@ function ($errno, $errstr, $errfile, $errline) {
                     }
                 }
                 continue;
-            } elseif (is_numeric($itemKey)) {
+            } elseif (is_int($itemKey)) {
                 // recurring tag (content), use parent tagname.
                 $childNode = $node->addChild($parentTagName);
-            } elseif (is_array($itemValue) && array_is_list($itemValue)) {
+            } elseif (is_array($itemValue) && is_int(array_key_first($itemValue))) {
                 // recurring tag, skip placeholder.
                 $childNode = $node;
             } else {