使用composer安装XHP时出错

Question

我尝试使用composer在OSX上安装XHP。我有一个composer.phar和composer.json的目录。我的composer.json文件如下所示：

{
    "require": {
            "facebook/xhp-lib": "~2.2"
    }
}

我还安装了最新版本的HHVM。我试过跑

hhvm composer.phar install --verbose

但出现以下错误：

[ErrorException]    
  Undefined index: 0  



Exception trace:
 () at phar://composer.phar/bin/../src/../vendor/symfony/process/Pipes/AbstractPipes.php:140
 Composer\Util\ErrorHandler::handle() at phar://composer.phar/bin/../src/../vendor/symfony/process/Pipes/AbstractPipes.php:140
 Symfony\Component\Process\Pipes\AbstractPipes->write() at phar://composer.phar/bin/../src/../vendor/symfony/process/Pipes/UnixPipes.php:98
 Symfony\Component\Process\Pipes\UnixPipes->readAndWrite() at phar://composer.phar/bin/../src/../vendor/symfony/process/Process.php:1359
 Symfony\Component\Process\Process->readPipes() at phar://composer.phar/bin/../src/../vendor/symfony/process/Process.php:1279
 Symfony\Component\Process\Process->updateStatus() at phar://composer.phar/bin/../src/../vendor/symfony/process/Process.php:305
 Symfony\Component\Process\Process->start() at phar://composer.phar/bin/../src/../vendor/symfony/process/Process.php:201
 Symfony\Component\Process\Process->run() at phar://composer.phar/bin/../src/../src/Composer/Util/ProcessExecutor.php:68
 Composer\Util\ProcessExecutor->execute() at phar://composer.phar/bin/../src/../src/Composer/Package/Version/VersionGuesser.php:88
 Composer\Package\Version\VersionGuesser->guessGitVersion() at phar://composer.phar/bin/../src/../src/Composer/Package/Version/VersionGuesser.php:67
 Composer\Package\Version\VersionGuesser->guessVersion() at phar://composer.phar/bin/../src/../src/Composer/Package/Loader/RootPackageLoader.php:76
 Composer\Package\Loader\RootPackageLoader->load() at phar://composer.phar/bin/../src/../src/Composer/Factory.php:332
 Composer\Factory->createComposer() at phar://composer.phar/bin/../src/../src/Composer/Factory.php:552
 Composer\Factory::create() at phar://composer.phar/bin/../src/../src/Composer/Console/Application.php:308
 Composer\Console\Application->getComposer() at phar://composer.phar/bin/../src/../src/Composer/Console/Application.php:420
 Composer\Console\Application->getPluginCommands() at phar://composer.phar/bin/../src/../src/Composer/Console/Application.php:131
 Composer\Console\Application->doRun() at phar://composer.phar/bin/../src/../vendor/symfony/console/Application.php:123
 Symfony\Component\Console\Application->run() at phar://composer.phar/bin/../src/../src/Composer/Console/Application.php:102
 Composer\Console\Application->run() at phar://composer.phar/bin/composer:43
 include() at /Users/chrisapa/Sites/project1/composer.phar:24

我不知道该怎么做。