Fix flaky subscribers policy rule unit test

Summary:
I'm about 90% sure this fixes the intermittent test failure on `testObjectSubscribersPolicyRule()` or whatever.

We use `spl_object_hash()` to identify objects when passing hints about policy changes to policy rules. This is hacky, and I think it's the source of the unit test issue.

Specifically, `spl_object_hash()` is approximately just returning the memory address of the object, and two objects can occasionally use the same memory address (one gets garbage collected; another uses the same memory).

If I replace `spl_object_hash()` with a static value like "zebra", the test failure reproduces.

Instead, sneak an object ID onto a runtime property. This is at least as hacky but shouldn't suffer from the same intermittent failure.

Test Plan: Ran `arc unit --everything`, but I never got a reliable repro of the issue in the first place, so who knows.

Reviewers: chad

Reviewed By: chad

Differential Revision: https://secure.phabricator.com/D17029

src/applications/policy/rule/PhabricatorPolicyRule.php

@@ -144,9 +144,30 @@ abstract class PhabricatorPolicyRule extends Phobject {
   private static function getObjectPolicyCacheKey(
     PhabricatorPolicyInterface $object,
     PhabricatorPolicyRule $rule) {
-    $hash = spl_object_hash($object);
-    $rule = get_class($rule);
-    return 'policycache.'.$hash.'.'.$rule;
+
+    // NOTE: This is quite a bit of a hack, but we don't currently have a
+    // better way to carry hints from the TransactionEditor into PolicyRules
+    // about pending policy changes.
+
+    // Put some magic secret unique value on each object so we can pass
+    // information about it by proxy. This allows us to test if pending
+    // edits to an object will cause policy violations or not, before allowing
+    // those edits to go through.
+
+    // Some better approaches might be:
+    //   - Use traits to give `PhabricatorPolicyInterface` objects real
+    //     storage (requires PHP 5.4.0).
+    //   - Wrap policy objects in a container with extra storage which the
+    //     policy filter knows how to unbox (lots of work).
+
+    // When this eventually gets cleaned up, the corresponding hack in
+    // LiskDAO->__set() should also be cleaned up.
+    static $id = 0;
+    if (!isset($object->_hashKey)) {
+      @$object->_hashKey = 'object.id('.(++$id).')';
+    }
+
+    return $object->_hashKey;
   }
 
 

src/infrastructure/storage/lisk/LiskDAO.php

@@ -1780,10 +1780,13 @@ abstract class LiskDAO extends Phobject {
    * @task   util
    */
   public function __set($name, $value) {
+    // Hack for policy system hints, see PhabricatorPolicyRule for notes.
+    if ($name != '_hashKey') {
       phlog(
         pht(
           'Wrote to undeclared property %s.',
           get_class($this).'::$'.$name));
+    }
     $this->$name = $value;
   }