Hooks and routes not working at all

Question

I have a module called hello_world.

I have a hello_world.info.yml file in drupal/web/modules/custom/hello_world whose content is the following.

name: Hello World
description: Hello World module
type: module
core: 8.x
package: Custom

This works perfectly ; the module is in the extension list.

I tried to make a help hook so I made in the same folder a hello_world.module file with the following code.

<?php

use Drupal\Core\Routing\RouteMatchInterface;

/**
 * Implements hook_help().
 */

function hello_world_help($route_name, RouteMatchInterface $route_match) {
    switch ($route_name) {
        case 'help.page.hello_world':
            $output = '';
            $output .= '<h3>' . t('About') . '</h3>';
            $output .= '<p>' . t('This is an example module.') . '</p>';
            return $output;
            break;
    }
}

This does not work at all. The help page is not shown.

I also tried to make a hello world page using this controller in drupal/web/modules/custom/hello_world/src/HelloWOrldCOntroller.php.

<?php

namespace Drupal\hello_world\Controller;

use Drupal\Core\Controller\ControllerBase;

/**
 * Controller for the salutation message.
 */
class HelloWorldController extends ControllerBase
{
    /**
     * Hello World.
     *
     * @return string
     */
    public function helloWorld()
    {
        return [
            '#markup' => $this->t('Hello World')
        ];
    }
}

I added hello_world.routing.yml to drupal/web/modules/custom/hello_world.

hello_world.hello:
path: '/hello'
defaults:
_controller:
'\Drupal\hello_world\Controller\HelloWorldController::helloWorld'
_title: 'Our first route'
requirements:
_permission: 'access content'

This does not work either, even after clearing the cache. As I said, the hello_world.info.yml works perfectly fine, but the help hook and the controller/routing does not. The rest of the core modules work. I am using Vagrant if it matters.

Answer 1

Creating the files is not enough: The module needs also to be installed. /admin/modules gives a list of modules and allows to install them.

After a module is installed, all its hooks are invoked from Drupal.

As side note, YAML files are required to use the correct indentation. The content of the hello_world.routing.yml file should be the following one.

hello_world.hello:
  path: '/hello'
  defaults:
    _controller: '\Drupal\hello_world\Controller\HelloWorldController::helloWorld'
    _title: 'Our first route'
  requirements:
    _permission: 'access content'

See the example give in Routing API, Registering simple routes.