From 27ce6918390088fbd6f786fb1a856d740bcf57b0 Mon Sep 17 00:00:00 2001
From: epriestley <git@epriestley.com>
Date: Wed, 9 Mar 2016 10:17:40 -0800
Subject: [PATCH] Fix an issue with the Herald engine field value cache

Summary:
To improve the performance of Herald, we attempt to generate the value for each field (e.g., a task title) only once.

For most field values this is cheap, but for some (like a commit's branches) it can be quite expensive. We only want to pay this cost once, so we cache field values.

However, D12957 accidentally added a check where we bypass the cache and generate the value for every field, before reading the cache. This causes us to generate each field for every rule that uses it, plus one extra time.

Instead, use the cache for this check, too. Also allow the cache to cache `null`, since it can be expensive to generate `null` even though the value isn't too interesting.

The value of this early hit isn't even used (we only care if it throws or not).

Test Plan:
  - Wrote a rule like "if any condition matches: branches contain a, branches contain b, branches contain c".
  - Put `phlog(new Exception())` in `DiffusionCommitBranchesHeraldField`.
  - Before patch, saw `bin/repository reparse --herald <any commit>` compute branches three times.
  - After patch, saw only one computation.
  - Verified field values in the transcript view

Reviewers: chad

Reviewed By: chad

Differential Revision: https://secure.phabricator.com/D15451
---
 src/applications/herald/engine/HeraldEngine.php | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/src/applications/herald/engine/HeraldEngine.php b/src/applications/herald/engine/HeraldEngine.php
index 00c063131a..df81117b80 100644
--- a/src/applications/herald/engine/HeraldEngine.php
+++ b/src/applications/herald/engine/HeraldEngine.php
@@ -274,7 +274,7 @@ final class HeraldEngine extends Phobject {
     } else {
       foreach ($conditions as $condition) {
         try {
-          $object->getHeraldField($condition->getFieldName());
+          $this->getConditionObjectValue($condition, $object);
         } catch (Exception $ex) {
           $reason = pht(
             'Field "%s" does not exist!',
@@ -366,14 +366,11 @@ final class HeraldEngine extends Phobject {
   }
 
   public function getObjectFieldValue($field) {
-    if (isset($this->fieldCache[$field])) {
-      return $this->fieldCache[$field];
+    if (!array_key_exists($field, $this->fieldCache)) {
+      $this->fieldCache[$field] = $this->object->getHeraldField($field);
     }
 
-    $result = $this->object->getHeraldField($field);
-
-    $this->fieldCache[$field] = $result;
-    return $result;
+    return $this->fieldCache[$field];
   }
 
   protected function getRuleEffects(