From 292f8fc612bd2d070110eb22877454937bfd7899 Mon Sep 17 00:00:00 2001
From: epriestley <git@epriestley.com>
Date: Sat, 26 Oct 2019 12:06:45 -0700
Subject: [PATCH] Fix an issue where added or removed source files could
 incorrectly select a DocumentEngine

Summary:
Ref T13425. The changes in D20865 could incorrectly lead to selection of a DocumentEngine that can not generate document diffs if a file was added or removed (for example, when a source file is added).

Move the engine pruning code to be shared -- we should always discard engines which can't generate a diff, even if we don't have both documents.

Test Plan: Viewed an added source file, no more document ref error arising from document engine selection.

Maniphest Tasks: T13425

Differential Revision: https://secure.phabricator.com/D20866
---
 .../parser/DifferentialChangesetParser.php           | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/src/applications/differential/parser/DifferentialChangesetParser.php b/src/applications/differential/parser/DifferentialChangesetParser.php
index 571405f64b..92d5f23c1a 100644
--- a/src/applications/differential/parser/DifferentialChangesetParser.php
+++ b/src/applications/differential/parser/DifferentialChangesetParser.php
@@ -1743,12 +1743,6 @@ final class DifferentialChangesetParser extends Phobject {
     if ($new_engines !== null && $old_engines !== null) {
       $shared_engines = array_intersect_key($new_engines, $old_engines);
       $default_engine = head_key($new_engines);
-
-      foreach ($shared_engines as $key => $shared_engine) {
-        if (!$shared_engine->canDiffDocuments($old_ref, $new_ref)) {
-          unset($shared_engines[$key]);
-        }
-      }
     } else if ($new_engines !== null) {
       $shared_engines = $new_engines;
       $default_engine = head_key($shared_engines);
@@ -1759,6 +1753,12 @@ final class DifferentialChangesetParser extends Phobject {
       return null;
     }
 
+    foreach ($shared_engines as $key => $shared_engine) {
+      if (!$shared_engine->canDiffDocuments($old_ref, $new_ref)) {
+        unset($shared_engines[$key]);
+      }
+    }
+
     $engine_key = $this->getDocumentEngineKey();
     if (strlen($engine_key)) {
       if (isset($shared_engines[$engine_key])) {