My custom block doesn't show up in the block library
<p>I am developing a custom module in Drupal 8. It shows data regarding some organizations that make use of our service. For this I have created a Controller that shows data from the database, which is put there by another module. From the scarce information and tutorials available on Drupal 8 developement I've been able to create the following. In the .routing.yml file I have created a path to this overview table like so (it doesn't properly copy here but the indents are okay): </p>

<pre><code>   OrganizationOverview.world:
     path: '/world'
     defaults:
       _controller:      'Drupal\OrganizationOverview\Controller\OrganizationOverviewController::overview'
    _title: 'World'
  requirements:
    _role: 'administrator'
    _permission: 'access content'
</code></pre>

<p>So now the overview is accessible with the URL <code>site.com/world</code>. But what we want is to show it on the frontpage or show it anywhere else on the site. For this it needs to be a Block. For this I have created an <code>OrganizationOverviewBlock</code> class in <code>OrganizationOverview/src/Plugin/Block/OrganizationOverviewBlock.php</code> which is the proper way according to the PSR-4 standard. The class looks like this:</p>

<pre><code>&lt;?php

namespace Drupal\OrganizationOverview\Plugin\Block;

use Drupal\Core\Block\BlockBase;
use Drupal\Core\Session\AccountInterface;

/**
 * Provides a 'OrganizationOverviewBlock' block.
 *
 * @Block(
 *  id = "organization_overview_block",
 *  admin_label = @Translation("OrganizationOverviewBlock"),
 *  category = @Translation("Custom")
 * )
 */
class OrganizationOverviewBlock extends BlockBase 
{


    public function build()
    {
        return array(
            '#markup' =&gt; 'Hello World',
        );
    }

    public function blockAccess(AccountInterface $account)
    {
        return $account-&gt;hasPermission('access content');
    }

}
</code></pre>

<p>So now it should show up in the Blocks Layout page (after flushing cache, which I do consistently) at <code>site.com/admin/structure/block/</code> as "Organization Overview Block" where I should enable it, according to plenty sources (<a href="https://www.drupal.org/node/2101565" rel="nofollow noreferrer">Create custom Block</a>, <a href="https://www.drupal.org/developing/api/8/block_api" rel="nofollow noreferrer">Block API Drupal 8</a>). But it doesn't show up there. I've tried implementing ContainerFactoryPluginInterface with some of those methods but that changes nothing. It does not show up. I've tried making a new test module with a block with the same code but a simpler name and it does not show up. I've copied the code to another platform (the production site) but it also doesn't show up there. What am I doing wrong? Can someone help me? I know Drupal 8 is new but this module really needs to be published soon.</p>