How to display a twig template via a controller's render array

Question

I'm trying to do something you'd think was simple, but I don't find good documentation for it.

I'm trying to create a controller that displays a twig template.

I've done the following so far:

1) In my module directory, I've created a templates/ directory. It contains a field-permission-description.html.twig file, containing mostly HTML text. So far, I don't even have any {{ twig_variables }} in it:

<div class='examples-description>

  <p>Field permision text will be here.</p>

</div>

2) I have a theme function in my MY_MODULE.module file:

/**
 * Implementation of hook_theme
 *
 * Since we have a lot to explain, we're going to use Twig to do it.
 */
function MY_MODULE_theme($existing, $type, $theme, $path) {
    return [
      'field_permission_description' => [
        'variables' => [
          'stuff' => NULL
        ]
      ]
    ];  
}

3) In my controller, the function returning the render array looks like this:

  /**
   * A simple controller method to explain what this example is about.
   */
  public function description() {
    $build = [
      'description' => [
        '#theme' => 'field_permission_description',
        '#stuff' => 'some stuff',
      ]
    ];
    return $build;
  }

I clear the cache with drush, and go to the page. There's no error, even in the watchdog, but the content region of the description page is blank; the template does not render.

It's not a problem with the controller, since if I substitute something else (say, just a little HTML in a #markup key), it renders fine.

There's been a couple of answers a year or two ago, but these all have things that no longer work as of RC1.

What do I need to do to get a twig template to render the way I'm trying to do here?

Answer 1

The problem turns out to be a missing ' mark in the twig file itself.

It turns out that the twig was rendering, but since I had

<div class='examples-description>

and not

<div class='examples-description'>

the browser refused to show the badly written HTML.

So this was user error, but a hard user error to debug. I saw what was going on by looking at the source for the page, which made it obvious.

Hopefully this will save folks some trouble. But in any event: the technique I use here is valid, and works if you don't do stupid things in your twig :-)