Symfony Demo Application - where to find twigs? - symfony

Question

I'm trying to orientate myself with Symfony framework by going through the "Symfony Demo application" and am trying to work my way through the interconnections. However in the below code snippet I can't find where this twig reference is getting defined value="{{ last_username }}":
\app\Resources\view\security\login.html.twig
{% extends 'base.html.twig' %}
{% block body_id 'login' %}
{% block main %}
{% if error %}
<div class="alert alert-danger">
{{ error.messageKey|trans(error.messageData) }}
</div>
{% endif %}
<div class="row">
<div class="col-sm-5">
<div class="well">
<form action="{{ path('security_login_check') }}" method="post">
<fieldset>
<legend><i class="fa fa-lock"></i> Secure Sign in</legend>
<div class="form-group">
<label for="username">Username</label>
<input type="text" id="username" name="_username" value="{{ last_username }}" class="form-control"/>
</div>
<div class="form-group">
<label for="password">Password:</label>
<input type="password" id="password" name="_password" class="form-control" />
</div>
<input type="hidden" name="_csrf_token" value="{{ csrf_token('authenticate') }}"/>
<button type="submit" class="btn btn-primary">
<i class="fa fa-sign-in"></i> Sign in
</button>
</fieldset>
</form>
</div>
</div>
I have searched the whole demo application for last_username and it only appears in these four files:
\app\cache\dev\classes.php
\app\cache\prod\classes.php
\vendor\symfony\symfony\src\Symfony\Component\Security\Core\SecurityContextInterface.php
\vendor\symfony\symfony\src\Symfony\Component\Security\Core\Security.php
...all of which don't seem to offer anything helpful of defining last_username.

Answer 1

The last_username parameter is passed to the template via the SecurityController, which is defined in the src/AppBundle/Controller/SecurityController.php file.
One of the coolest features of the Symfony Demo application is that all pages include a Show code which shows you both the controller and the template used to create the page you are looking at. For example, in the case of the login page: