Is a Twig block empty? - Symfony 2 - symfony

Question

I have a twig template with the following block:
{% block dashboard %}
{% include "::user_dashboard.html.twig" %}
{% endblock dashboard %}
Later in that template, I want to set a class on a div based on whether or not there is anything in that block (i.e., by default, it will have the include above, but children of this template may override it and empty it out).
What I had (that somewhat worked) was ...
{% set _dashboard = block('dashboard') %}
{% set _mainWidth = ( _dashboard|trim is empty ? "no-dashboard" : "with-dashboard" ) #}
<div id="main" class="{{ _mainWidth }}">
The problem here is that whole dashboard block gets called twice. This wouldn't bother me too much except that block renders a few controller actions, i.e. ...
{% render "UserWidget:userAppMenu" %}
... and the code in that action is being called twice. For various reasons, not the least of which is performance, this messes with some of the stuff in that dashboard block.
So, my question is ... is there any way to tell if that block is empty without loading it twice? Is there something really simple I'm missing or is this even possible?
Thanks!
EDIT:
Here is my full template if it helps clarify things:
{% extends '::base.html.twig' %}
{% block layout %}
{% block header %}
{% include "::header.html.twig" %}
{% endblock header %}
<div id="container" class="row-fluid">
{% block dashboard %}
{% include "::user_dashboard.html.twig" %}
{% endblock dashboard %}
{% set _dashboard = block('dashboard') %}
{% set _mainWidth = ( _dashboard|trim is empty ? "no-dashboard" : "with-dashboard" ) %}
<div id="main" class="{{ _mainWidth }}">
<h1 class="page-title">{% block page_title %}{% endblock %}</h1>
{% block main_filters %}{% endblock %}
{% if app.session.flashbag.has('message') %}
<div class="alert alert-block alert-success">
<ul>
{% for flashMessage in app.session.flashbag.get('message') %}
<li>{{ flashMessage }}</li>
{% endfor %}
</ul>
</div>
{% endif %}
{% if app.session.flashbag.has('warning') %}
<div class="alert alert-block alert-success">
<ul>
{% for flashWarning in app.session.flashbag.get('warning') %}
<li>{{ flashWarning }}</li>
{% endfor %}
</ul>
</div>
{% endif %}
{% block body %}{% endblock %}
{% block footer %}
{% include "::footer.html.twig" %}
{% endblock footer %}
</div>
</div>
{% endblock layout %}
Here you can see on lines 11 and 15 - both of those actually seem to include and process what is in that include.

Answer 1

What about this? This way the block should only be rendered once, when you call block('dashboard').
{# at top of twig #}
{% set _dashboard = block('dashboard') %}
{# where ever you include your block #}
<div>
{{ _dashboard|raw }}
</div>
{# and your main #}
{% set _mainWidth = ( _dashboard|trim is empty ? "no-dashboard" : "with-dashboard" ) #}
<div id="main" class="{{ _mainWidth }}">