Promote instance identity to the upstream and pass it to commit hooks

Summary:
Fixes T7019. In a cluster environment, pushes currently fail because the commit hook can't identify the instance.

For web processes, the hostname identifies the instance -- but we don't have a hostname in the hook.

For CLI processes, the environment identifies the instance -- but we don't have an environment in the hook under SVN.

Promote the instance identifier into the upstream and pack/unpack it explicitly for hooks. This is probably not useful for anyone but us, but the amount of special-purpose code we're introducing is very small.

I poked at trying to do this in a more general way, but:

  - We MUST know this BEFORE we run code, so the normal subclassing stuff is useless.
  - I couldn't come up with any other parameter which might ever be useful to pass in.

Test Plan: Used `git push` to push code through proxied HTTP, got a clean push.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T7019

Differential Revision: https://secure.phabricator.com/D11495

scripts/repository/commit_hook.php

@@ -1,6 +1,25 @@
 #!/usr/bin/env php
 <?php
 
+// Commit hooks execute in an unusual context where the environment may be
+// unavailable, particularly in SVN. The first parameter to this script is
+// either a bare repository identifier ("X"), or a repository identifier
+// followed by an instance identifier ("X:instance"). If we have an instance
+// identifier, unpack it into the environment before we start up. This allows
+// subclasses of PhabricatorConfigSiteSource to read it and build an instance
+// environment.
+
+if ($argc > 1) {
+  $context = $argv[1];
+  $context = explode(':', $context, 2);
+  $argv[1] = $context[0];
+
+  if (count($context) > 1) {
+    $_ENV['PHABRICATOR_INSTANCE'] = $context[1];
+    putenv('PHABRICATOR_INSTANCE='.$context[1]);
+  }
+}
+
 $root = dirname(dirname(dirname(__FILE__)));
 require_once $root.'/scripts/__init_script__.php';