Impossible to install or update when prestissimo is installed

[groovytron]

Container version: php:7.1

Command to reproduce

$ composer install

Error

Downloading https://repo.packagist.org/packages.json                                                                                                                                                                                                           
                                                                                                                                                                                                                                                               
                                                                                                                                                                                                                                                               
  [ErrorException]                                                                                                                                                                                                                                             
  mkdir(): Not a directory                                                                                                                                                                                                                                     
                                                                                                                                                                                                                                                               
                                                                                                                                                                                                                                                               
Exception trace:                                                                                                                                                                                                                                               
 () at /home/dev/.composer/vendor/hirak/prestissimo/src/CopyRequest.php:103                                                                                                                                                                                    
 Composer\Util\ErrorHandler::handle() at n/a:n/a                                                                                                                                                                                                               
 mkdir() at /home/dev/.composer/vendor/hirak/prestissimo/src/CopyRequest.php:103                                                                                                                                                                               
 Hirak\Prestissimo\CopyRequest->createDir() at /home/dev/.composer/vendor/hirak/prestissimo/src/CopyRequest.php:89                                                                                                                                             
 Hirak\Prestissimo\CopyRequest->setDestination() at /home/dev/.composer/vendor/hirak/prestissimo/src/CopyRequest.php:39                                                                                                                                        
 Hirak\Prestissimo\CopyRequest->__construct() at /home/dev/.composer/vendor/hirak/prestissimo/src/ParallelizedComposerRepository.php:26                                                                                                                        
 Hirak\Prestissimo\ParallelizedComposerRepository->preloadProviderListings() at /home/dev/.composer/vendor/hirak/prestissimo/src/ParallelizedComposerRepository.php:39                                                                                         
 Hirak\Prestissimo\ParallelizedComposerRepository->prefetch() at /home/dev/.composer/vendor/hirak/prestissimo/src/Plugin.php:150                                                                                                                               
 Hirak\Prestissimo\Plugin->prefetchComposerRepositories() at /home/dev/.composer/vendor/hirak/prestissimo/src/Plugin.php:82                                                                                                                                    
 Hirak\Prestissimo\Plugin->activate() at phar:///usr/local/bin/composer/src/Composer/Plugin/PluginManager.php:236                                                                                                                                              
 Composer\Plugin\PluginManager->addPlugin() at phar:///usr/local/bin/composer/src/Composer/Plugin/PluginManager.php:205                                                                                                                                        
 Composer\Plugin\PluginManager->registerPackage() at phar:///usr/local/bin/composer/src/Composer/Plugin/PluginManager.php:261                                                                                                                                  
 Composer\Plugin\PluginManager->loadRepository() at phar:///usr/local/bin/composer/src/Composer/Plugin/PluginManager.php:79                                                                                                                                    
 Composer\Plugin\PluginManager->loadInstalledPlugins() at phar:///usr/local/bin/composer/src/Composer/Factory.php:384                                                                                                                                          
 Composer\Factory->createComposer() at phar:///usr/local/bin/composer/src/Composer/Factory.php:576                                                                                                                                                             
 Composer\Factory::create() at phar:///usr/local/bin/composer/src/Composer/Console/Application.php:345                                                                                                                                                         
 Composer\Console\Application->getComposer() at phar:///usr/local/bin/composer/src/Composer/Console/Application.php:458                                                                                                                                        
 Composer\Console\Application->getPluginCommands() at phar:///usr/local/bin/composer/src/Composer/Console/Application.php:156                                                                                                                                  
 Composer\Console\Application->doRun() at phar:///usr/local/bin/composer/vendor/symfony/console/Application.php:117                                                                                                                                            
 Symfony\Component\Console\Application->run() at phar:///usr/local/bin/composer/src/Composer/Console/Application.php:104
 Composer\Console\Application->run() at phar:///usr/local/bin/composer/bin/composer:61
 require() at /usr/local/bin/composer:24

[groovytron]

If you set the environment variable COMPOSER_CACHE_DIR to /dev/null in your container, you will get this error because prestissimo tries to write into it and it's writable for anybody except `root.

So don't set it to /dev/null and simply clear your cache with composer in your container at startup if you don't want any cache.

Or use the --no-cache option to avoid using the cache. (https://getcomposer.org/doc/03-cli.md#global-options).

[groovytron]

This information should be documented in the README.