New Symfony 3 installation: Could not open input file: app/console in composer install

Just create var directory. After that composer install and composer update will work ok.

Explanation:

vendor/sensio/distribution-bundle/Composer/ScriptHandler.php:462

protected static function useNewDirectoryStructure(array $options)
{
    return isset($options['symfony-var-dir']) && is_dir($options['symfony-var-dir']);
}

So you need both to have symfony-var-dir in composer.json's extra and have this directory existing.

The ScriptHandler take the dir from the extra config key in the composer.json files names as symfony-bin-dir. So check that the composer contain the correct configuration key, as example:

composer.json

....
"extra": {
    "symfony-app-dir": "app",
    "symfony-bin-dir": "bin",
    "symfony-var-dir": "var",
    ....

EDIT:

The problem was related to the cache of composer. It was solved clearing it with the command:

>php composer.phar clear-cache

Hope this helps.

I have been running into the same problem. The script uses the existance of the var directory to decide whether to use the new directory structure or the old one. If var exists, the new directory structure is used. Otherwise it uses the old structure.

The default .gitignore file prevents both the var directory and the bin directory from being added to git.

What I did to solve the problem for me was to edit .gitignore in the project directory so that it looks like this:

/app/config/parameters.yml
/bin/*
/build/
/composer.phar
/vendor/
/web/bundles/
/var/*
!var/cache
/var/cache/*
!var/cache/.gitkeep
!var/logs
/var/logs/*
!var/logs/.gitkeep
!var/sessions
/var/sessions/*
!var/sessions/.gitkeep
!bin/console
!bin/symfony_requirements
/phpunit.xml

I do not pretend to be an expert on .gitignore, so I'm not sure that is the most elegant way of doing it, but it is what worked for me.