Migrating PHP templates to Twig

Tip: if you're using VS Code, install this plugin: bajdzis.vscode-twig-pack

Basic migration

PHP

<?php
$view->extend('MauticCoreBundle:Default:content.html.php');
$view['slots']->set('mauticContent', 'mauticWebhook');
$view['slots']->set('headerTitle', $view['translator']->trans('mautic.webhook.webhooks'));
?>

// ROUTING
<a href="<?php echo $view['router']->path('/emails', ['objectAction' => 'batchDelete']); ?">Hello world!</a>

// FORMS
<?php echo $view['form']->start($form); ?>
<?php echo $view['form']->row($form['email']); ?>
<?php echo $view['form']->end($form); ?>

// PAGE ACTIONS
$view['slots']->set('actions', $view->render('MauticCoreBundle:Helper:page_actions.html.php', [
    'item'            => $item,
    'templateButtons' => [
        'edit'   => $view['security']->hasEntityAccess($permissions['webhook:webhooks:editown'], $permissions['webhook:webhooks:editother'], $item->getCreatedBy()),
        'clone'  => $permissions['webhook:webhooks:create'],
        'delete' => $view['security']->hasEntityAccess($permissions['webhook:webhooks:deleteown'], $permissions['webhook:webhooks:deleteown'], $item->getCreatedBy()),
    ],
    'routeBase' => 'webhook',
]));

// TODO add more examples

Becomes

Twig

{% extends '@MauticCore/Default/content.html.twig' %}

{% block headerTitle %}{% trans %}mautic.webhook.webhooks{% endtrans %}{% endblock %}
{% block mauticContent %}mauticWebhook{% endblock %}

{# ROUTING #}
<a href="{{ path('/emails', {objectAction: 'batchDelete'}) }}">Hello world!</a>

{# FORMS #}
{{ form_start(form) }}
{{ form_row(form.email) }}
{{ form_end(form) }}

{# PAGE ACTIONS #}
{% block actions %}
    {{- include(
        '@MauticCore/Helper/page_actions.html.twig', {
            item: item,
            templateButtons: {
                'edit': securityHasEntityAccess(
                    permissions['webhook:webhooks:editown'],
                    permissions['webhook:webhooks:editother'],
                    item.getCreatedBy()
                ),
                'clone': permissions['webhook:webhooks:create'],
                'delete': securityHasEntityAccess(
                    permissions['webhook:webhooks:deleteown'],
                    permissions['webhook:webhooks:deleteother'],
                    item.getCreatedBy()
                )
            },
            routeBase: 'webhook'
    }) -}}
{% endblock %}

{# TODO add more examples #}

Random notes

strict_variables is enabled both in dev mode (config_dev.php) and in prod mode (config_prod.php) to help you prevent bugs in your code. See the Twig documentation for more details.
If you extend MauticCoreBundle:Default:content.html.twig, everything HAS to be in blocks. Trying to put any HTML elements outside a block will fail with the following error:

A template that extends another one cannot include content outside Twig blocks.
If you need to extend a Twig template but also need to override variabes inside of it, you can use Embed(embed) instead. This tag combines the functionality of include and extends.
You're probably used to writing if !empty($variable) {} in PHP. That checks if the variable is set and whether it is not empty. In Twig, you explicity have to write if variable is defined and variable is not empty. It's a lot more descriptive. In some cases, you can use Twig's default filter, like:
Twig
```
Before:

{% set nameGetter = nameGetter is defined and nameGetter is not empty ? nameGetter : 'getName' %}

After:

{% set nameGetter = nameGetter|default('getName') %}
```
Regarding the default filter: pay special attention to the documented use case where false is treated as an empty value. Consider using ?? true instead of |default(true) when using the default filter on a variable that could already have a boolean value set.

You can use text replacement with the {% trans %} tag as a built-in functionality:

{% trans with {'%code%': status_code} %}message{% endtrans %}

Alternatively, you can use the more compact |trans filter instead.:

{{ message|trans({'%code%': status_code}) }}
```    
The nice thing about using filters, is that you can chain them:
```
{{ message|striptags|trans({'%code%': status_code}) }}
```

Symfony Best Practices for Templates
Twig for Template Designers is a good overview on creating templates.