From 61c934449d17062786bfe7eaf31ae1bd05b2be7f Mon Sep 17 00:00:00 2001
From: epriestley <git@epriestley.com>
Date: Wed, 11 Dec 2013 14:46:46 -0800
Subject: [PATCH] Fix fatal in Git hook when a --force push completely rewrites
 a ref

Summary: Fixes T4224. If you `git merge-base A B`, and they have //no// ancestor, the command exits with an error. Assume errors mean "no ancestry" and continue.

Test Plan: Completely rewrite a repository with a `--force` push.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T4224

Differential Revision: https://secure.phabricator.com/D7756
---
 .../engine/DiffusionCommitHookEngine.php          | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/src/applications/diffusion/engine/DiffusionCommitHookEngine.php b/src/applications/diffusion/engine/DiffusionCommitHookEngine.php
index b76c4b8549..d57f4480bb 100644
--- a/src/applications/diffusion/engine/DiffusionCommitHookEngine.php
+++ b/src/applications/diffusion/engine/DiffusionCommitHookEngine.php
@@ -256,8 +256,19 @@ final class DiffusionCommitHookEngine extends Phobject {
     }
 
     foreach (Futures($futures)->limit(8) as $key => $future) {
-      list($stdout) = $future->resolvex();
-      $updates[$key]['merge-base'] = rtrim($stdout, "\n");
+
+      // If 'old' and 'new' have no common ancestors (for example, a force push
+      // which completely rewrites a ref), `git merge-base` will exit with
+      // an error and no output. It would be nice to find a positive test
+      // for this instead, but I couldn't immediately come up with one. See
+      // T4224. Assume this means there are no ancestors.
+
+      list($err, $stdout) = $future->resolve();
+      if ($err) {
+        $updates[$key]['merge-base'] = null;
+      } else {
+        $updates[$key]['merge-base'] = rtrim($stdout, "\n");
+      }
     }
 
     return $updates;