I've created a "PoC" project in order to ease with the bug reproduction, you can find it here: https://github.com/1ma/symfony-cmd-issue

Project contents

A brand new Symfony3 project with an empty entity (Test), its companion repository (TestRepository) and a command (TestCommand) defined as a service, as per the cookbook entry found at http://symfony.com/doc/current/cookbook/console/commands_as_services.html

# app/config/services.yml
services:
    test_repo:
        class: AppBundle\Repository\TestRepository
        factory: ["@doctrine.orm.default_entity_manager", getRepository]
        arguments: ["AppBundle:Test"]

    test_command:
        class: AppBundle\Command\TestCommand
        arguments:
            - "@test_repo"
        tags:
            - { name: console.command }

Steps to reproduce

1. $ git clone https://github.com/1ma/symfony-cmd-issue.git

2. $ cd symfony-cmd-issue; composer install

   When the prompt shows up, be sure to set valid values for database_user and database_password. They should map to a MySQL user with enough permissions to create the database.

3. At this point the installation will break. Further calls to bin/console will also fail with the following error message:

   marcel@workstation:~/workspace/symfony-cmd-issue$ php bin/console
   
   [Doctrine\DBAL\Exception\ConnectionException]                                      
   An exception occured in driver: SQLSTATE[42000] [1049] Unknown database 'symfony'  
   
   
   [Doctrine\DBAL\Driver\PDOException]                
   SQLSTATE[42000] [1049] Unknown database 'symfony'  
   
   
   [PDOException]                                     
   SQLSTATE[42000] [1049] Unknown database 'symfony'
   

4. In order to restore the console, remove the tags: block from the command service definition. Now you'll be able to execute the console and create the database:

   marcel@workstation:~/workspace/symfony-cmd-issue$ php bin/console doctrine:database:create
   Created database `symfony` for connection named default
   

5. Once the database is created you can restore the tags: block in the command service definition and the console will still work:

   marcel@workstation:~/workspace/symfony-cmd-issue$ php bin/console cmd:test
   AppBundle\Entity\Test
   

6. Drop the database, and the console breaks again:

   marcel@workstation:~/workspace/symfony-cmd-issue$ php bin/console doctrine:database:drop --force
   Dropped database for connection named `symfony`
   
   marcel@workstation:~/workspace/symfony-cmd-issue$ php bin/console cmd:test
   
   
   [Doctrine\DBAL\Exception\ConnectionException]                                      
   An exception occured in driver: SQLSTATE[42000] [1049] Unknown database 'symfony'  
   
   
   [Doctrine\DBAL\Driver\PDOException]                
   SQLSTATE[42000] [1049] Unknown database 'symfony'  
   
   
   [PDOException]                                     
   SQLSTATE[42000] [1049] Unknown database 'symfony'  
   

Troubleshooting

From what I've seen from the above exception stack trace, it seems that every service tagged with the console.command tag is instantiated at Application::registerCommands().

Then, if one of the command dependencies is a subclass of EntityRepository instantiated as EntityManager->getRepository('AppBundle:EntityName') a connection to the database will be always attempted down the line, even if it doesn't exist yet.

Here is the full stack trace with some of the most relevant entries highlighted in bold font:
#0 .../symfony-cmd-issue/vendor/doctrine/dbal/lib/Doctrine/DBAL/Driver/PDOMySql/Driver.php(45): Doctrine\DBAL\Driver\PDOConnection::__construct('mysql:host=127....', 'root', 'root', Array)

#1 .../symfony-cmd-issue/vendor/doctrine/dbal/lib/Doctrine/DBAL/Connection.php(360): Doctrine\DBAL\Driver\PDOMySql\Driver->connect(Array, 'root', 'root', Array)
#2 .../symfony-cmd-issue/vendor/doctrine/dbal/lib/Doctrine/DBAL/Connection.php(429): Doctrine\DBAL\Connection->connect()
#3 .../symfony-cmd-issue/vendor/doctrine/dbal/lib/Doctrine/DBAL/Connection.php(389): Doctrine\DBAL\Connection->getDatabasePlatformVersion()
#4 .../symfony-cmd-issue/vendor/doctrine/dbal/lib/Doctrine/DBAL/Connection.php(328): Doctrine\DBAL\Connection->detectDatabasePlatform()
#5 .../symfony-cmd-issue/vendor/doctrine/orm/lib/Doctrine/ORM/Mapping/ClassMetadataFactory.php(763): Doctrine\DBAL\Connection->getDatabasePlatform()

#6 .../symfony-cmd-issue/vendor/doctrine/orm/lib/Doctrine/ORM/Mapping/ClassMetadataFactory.php(616): Doctrine\ORM\Mapping\ClassMetadataFactory->getTargetPlatform()
#7 .../symfony-cmd-issue/vendor/doctrine/orm/lib/Doctrine/ORM/Mapping/ClassMetadataFactory.php(174): Doctrine\ORM\Mapping\ClassMetadataFactory->completeIdGeneratorMapping(Object(Doctrine\ORM\Mapping\ClassMetadata))
#8 .../symfony-cmd-issue/vendor/doctrine/common/lib/Doctrine/Common/Persistence/Mapping/AbstractClassMetadataFactory.php(332): Doctrine\ORM\Mapping\ClassMetadataFactory->doLoadMetadata(Object(Doctrine\ORM\Mapping\ClassMetadata), NULL, false, Array)
#9 .../symfony-cmd-issue/vendor/doctrine/orm/lib/Doctrine/ORM/Mapping/ClassMetadataFactory.php(78): Doctrine\Common\Persistence\Mapping\AbstractClassMetadataFactory->loadMetadata('AppBundle\Entit...')
#10 .../symfony-cmd-issue/vendor/doctrine/common/lib/Doctrine/Common/Persistence/Mapping/AbstractClassMetadataFactory.php(216): Doctrine\ORM\Mapping\ClassMetadataFactory->loadMetadata('AppBundle\Entit...')
#11 .../symfony-cmd-issue/vendor/doctrine/orm/lib/Doctrine/ORM/EntityManager.php(281): Doctrine\Common\Persistence\Mapping\AbstractClassMetadataFactory->getMetadataFor('AppBundle:Test')
#12 .../symfony-cmd-issue/vendor/doctrine/orm/lib/Doctrine/ORM/Repository/DefaultRepositoryFactory.php(44): Doctrine\ORM\EntityManager->getClassMetadata('AppBundle:Test')
#13 .../symfony-cmd-issue/vendor/doctrine/orm/lib/Doctrine/ORM/EntityManager.php(698): Doctrine\ORM\Repository\DefaultRepositoryFactory->getRepository(Object(Doctrine\ORM\EntityManager), 'AppBundle:Test')

#14 .../symfony-cmd-issue/var/cache/dev/appDevDebugProjectContainer.php(2465): Doctrine\ORM\EntityManager->getRepository('AppBundle:Test')
#15 .../symfony-cmd-issue/vendor/symfony/symfony/src/Symfony/Component/DependencyInjection/Container.php(273): appDevDebugProjectContainer->getTestRepoService()

#16 .../symfony-cmd-issue/var/cache/dev/appDevDebugProjectContainer.php(2452): Symfony\Component\DependencyInjection\Container->get('test_repo')
#17 .../symfony-cmd-issue/vendor/symfony/symfony/src/Symfony/Component/DependencyInjection/Container.php(273): appDevDebugProjectContainer->getTestCommandService()

#18 .../symfony-cmd-issue/vendor/symfony/symfony/src/Symfony/Bundle/FrameworkBundle/Console/Application.php(101): Symfony\Component\DependencyInjection\Container->get('test_command')
#19 .../symfony-cmd-issue/vendor/symfony/symfony/src/Symfony/Bundle/FrameworkBundle/Console/Application.php(71): Symfony\Bundle\FrameworkBundle\Console\Application->registerCommands()
#20 .../symfony-cmd-issue/vendor/symfony/symfony/src/Symfony/Component/Console/Application.php(117): Symfony\Bundle\FrameworkBundle\Console\Application->doRun(Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#21 .../symfony-cmd-issue/bin/console(29): Symfony\Component\Console\Application->run(Object(Symfony\Component\Console\Input\ArgvInput))
#22 {main}

Further details

Tested on a Debian Jessie x64 virtual machine with PHP 5.6, Symfony 3.0.2 and Doctrine ORM 2.5.4