Format generated config files using the short array syntax

[cykirsch]

Description

1. Magento is following a standard of new code using short array syntax (Coding standards: arrays #758).
2. Magento has an automated checker to enforce the short array syntax precommit (https://github.com/magento/magento2/blob/2.2/.php_cs.dist#L31).
3. Magento recommends checking in app/etc/config.php (http://devdocs.magento.com/guides/v2.2/config-guide/config/config-php.html)

Check this file in to source control and use it in your development, staging, and production systems.

4. Magento's auto-generated app/etc/config.php uses the long array syntax.

Put that all together and the auto-generated config doesn't match the required standards to be checked in. The change made in this PR is to modify PhpFormatter to recursively return the array representation using short array syntax [] instead of long array(). If the given variable is not an array, it uses the standard var_export behavior.

Manual testing scenarios

1. bin/magento setup:upgrade
2. app/etc/config.php should use the short array syntax

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)

[cykirsch]

As an added note, I did attempt to do this using Zend\Code\Generator\ValueGenerator instead of var_export, but the array depth wasn't being tracked properly. The unit test array would look like this

[
  'ns1' => [
        's1' => [
            's11',
            's12',
        ],
        's2' => [
            's21',
            's22',
        ],
    ],
  'ns2' => [
        's1' => [
            's11',
        ],
    ],
  'ns3' => 'just text',
  'ns4' => 'just text',
]

[ishakhsuvarov]

Please avoid variables with unclear names. $r does not really describe what is it for.

[ishakhsuvarov]

Please take advantage of PHP 7.0 syntax (type hints and return types for methods)

[ishakhsuvarov]

Is there any specific reason not to use is_array?
Additionally, readability may be slightly improved by reversing the logic like

if (!is_array($var)) {
    return var_export($var, true);
}
/// Transforming to short array syntax here
...

[ishakhsuvarov]

Please add a description for the constant (docBlock)

[cykirsch]

@ishakhsuvarov @okorshenko I was more or less expecting these changes would be in 2.2.2. Is it odd to you that it is on the 2.2.2-preview branch but not on the 2.2.2 tag? Or does that happen often?

[clemblanco]

What if we want 4 spaces tab indentation? Shouldn't this follow a PSR?

[cykirsch]

@clementblanco That did cross my mind, and I would prefer it as well, but I neglected to do it...I think because I was continuing to use var_export and I didn't want to mix 4 and 2.