From 9eb285f4aabb27b8e3cb144a9e020ee1ac0fa747 Mon Sep 17 00:00:00 2001
From: epriestley <git@epriestley.com>
Date: Wed, 17 May 2017 08:25:39 -0700
Subject: [PATCH] Fix "left"/"right" changeset ID selection for synthetic
 deletions

Summary:
Fixes T8323. See that task for a description.

We were using `nonempty()`, but that rule doesn't cover synthetic deletions (file present in an earlier diff, but no longer present in the later diff).

Test Plan: Followed the steps in T8323, got a clean comment.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T8323

Differential Revision: https://secure.phabricator.com/D17929
---
 .../view/DifferentialChangesetDetailView.php  | 24 +++++++++++++++----
 1 file changed, 20 insertions(+), 4 deletions(-)

diff --git a/src/applications/differential/view/DifferentialChangesetDetailView.php b/src/applications/differential/view/DifferentialChangesetDetailView.php
index 219dfaaa1f..42be1c6444 100644
--- a/src/applications/differential/view/DifferentialChangesetDetailView.php
+++ b/src/applications/differential/view/DifferentialChangesetDetailView.php
@@ -150,15 +150,31 @@ final class DifferentialChangesetDetailView extends AphrontView {
     $renderer = DifferentialChangesetHTMLRenderer::getHTMLRendererByKey(
       $this->getRenderer());
 
+    $changeset_id = $this->changeset->getID();
+
+    $vs_id = $this->getVsChangesetID();
+    if (!$vs_id) {
+      // Showing a changeset normally.
+      $left_id = $changeset_id;
+      $right_id = $changeset_id;
+    } else if ($vs_id == -1) {
+      // Showing a synthetic "deleted" changeset for a file which was
+      // removed between changes.
+      $left_id = $changeset_id;
+      $right_id = null;
+    } else {
+      // Showing a diff-of-diffs.
+      $left_id = $vs_id;
+      $right_id = $changeset_id;
+    }
+
     return javelin_tag(
       'div',
       array(
         'sigil' => 'differential-changeset',
         'meta'  => array(
-          'left'  => nonempty(
-            $this->getVsChangesetID(),
-            $this->changeset->getID()),
-          'right' => $this->changeset->getID(),
+          'left'  => $left_id,
+          'right' => $right_id,
           'renderURI' => $this->getRenderURI(),
           'whitespace' => $this->getWhitespace(),
           'highlight' => null,