Pass GIT_ENVIRONMENTAL_MAGIC through to hook subprocesses to support Git 2.11.0

Summary:
Fixes T11940. In 2.11.0, Git has made a change so that newly-pushed changes are held in a temporary area until the hook accepts or rejects them.

This magic temporary area is only readable if the appropriate `GIT_ENVIRONMENTAL_MAGIC` variables are available. When executing `git` commands, pass them through from the calling context.

We're intentionally conservative about which variables we pass, and with good reason (see "httpoxy" in T11359). I think this continues to be the correct default behavior.

Test Plan:
  - Upgraded to Git 2.11.0.
  - Tried to push over SSH, got a hook error.
  - Applied patch.
  - Pulled and pushed over SSH.
  - Pulled and pushed over HTTP.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T11940

Differential Revision: https://secure.phabricator.com/D16988

src/applications/diffusion/engine/DiffusionCommitHookEngine.php

@@ -610,7 +610,11 @@ final class DiffusionCommitHookEngine extends Phobject {
       self::ENV_REMOTE_ADDRESS => $this->getRemoteAddress(),
     );
 
-    $directories = $this->getRepository()->getHookDirectories();
+    $repository = $this->getRepository();
+
+    $env += $repository->getPassthroughEnvironmentalVariables();
+
+    $directories = $repository->getHookDirectories();
     foreach ($directories as $directory) {
       $hooks = $this->getExecutablesInDirectory($directory);
       sort($hooks);

src/applications/diffusion/protocol/DiffusionCommandEngine.php

@@ -209,6 +209,8 @@ abstract class DiffusionCommandEngine extends Phobject {
       }
     }
 
+    $env += $repository->getPassthroughEnvironmentalVariables();
+
     return $env;
   }
 

src/applications/repository/storage/PhabricatorRepository.php

@@ -2015,6 +2015,57 @@ final class PhabricatorRepository extends PhabricatorRepositoryDAO
     return $client;
   }
 
+  public function getPassthroughEnvironmentalVariables() {
+    $env = $_ENV;
+
+    if ($this->isGit()) {
+      // $_ENV does not populate in CLI contexts if "E" is missing from
+      // "variables_order" in PHP config. Currently, we do not require this
+      // to be configured. Since it may not be, explictitly bring expected Git
+      // environmental variables into scope. This list is not exhaustive, but
+      // only lists variables with a known impact on commit hook behavior.
+
+      // This can be removed if we later require "E" in "variables_order".
+
+      $git_env = array(
+        'GIT_OBJECT_DIRECTORY',
+        'GIT_ALTERNATE_OBJECT_DIRECTORIES',
+        'GIT_QUARANTINE_PATH',
+      );
+      foreach ($git_env as $key) {
+        $value = getenv($key);
+        if (strlen($value)) {
+          $env[$key] = $value;
+        }
+      }
+
+      $key = 'GIT_PUSH_OPTION_COUNT';
+      $git_count = getenv($key);
+      if (strlen($git_count)) {
+        $git_count = (int)$git_count;
+        $env[$key] = $git_count;
+        for ($ii = 0; $ii < $git_count; $ii++) {
+          $key = 'GIT_PUSH_OPTION_'.$ii;
+          $env[$key] = getenv($key);
+        }
+      }
+    }
+
+    $result = array();
+    foreach ($env as $key => $value) {
+      // In Git, pass anything matching "GIT_*" though. Some of these variables
+      // need to be preserved to allow `git` operations to work properly when
+      // running from commit hooks.
+      if ($this->isGit()) {
+        if (preg_match('/^GIT_/', $key)) {
+          $result[$key] = $value;
+        }
+      }
+    }
+
+    return $result;
+  }
+
 /* -(  Repository URIs  )---------------------------------------------------- */