Symfony3 Variable does not exist in including template - php

Question

I get the following error: Variable "file" does not exist.
The included template Contractor:file.html.twig looks like this:
{{ dump(file) }}
The main template form.html.twig looks like this:
{% extends '::base.html.twig' %}
{% form_theme form 'NaSoftEdmBundle:Form:fields.html.twig' %}
...
{% block files %}
{% for file in form.files %}
{{ include('NaSoftEdmBundle:Contractor:file.html.twig', {'file': file}) }}
{% endfor %}
{% endblock %}
Controller:
public function editAction(Request $request, Contractor $contractor)
{
...
return $this->render('NaSoftEdmBundle:Contractor:form.html.twig', array(
'form' => $form->createView(),
));
}
But when I try to display a variable inside the main template file (form.html.twig), the variable becomes available:
{% for file in form.files %}
{{ dump(file) }} {# it work! #}
{% endfor %}
ContractorFile {#499 ▼
-id: 154
-uploadedFile: null
-name: "57c6d217d9a92.jpg"
-origName: "1471590585502.jpg"
-path: "/contractor/docs/files/2/335"
-size: 153536
-mimeType: "image/jpeg"
-updateDate: DateTime {#496 ▶}
-contractor: Contractor {#370 ▶}
}
command php app/console cache:clear did not help

Answer 1

The problem was that I was before starting the cycle "for" included the same template for attribute data-prototype:
data-prototype="{% filter escape %}
{% include 'NaSoftEdmBundle: Contractor: file.html.twig' with { '_form':form.files.vars.prototype} %}
{% endfilter %}"
I've created for the attribute "data-prototype" new template and it worked.
data-prototype="{% filter escape %}
{% include 'NaSoftEdmBundle: Contractor: filePrototype.html.twig' with { 'file':_form.files.vars.prototype} %}
{% endfilter %}"
This has been implemented to customize the template collection

Answer 2

The correct way to pass variables to a Twig include command is this:
{% include 'NaSoftEdmBundle:Contractor:file.html.twig' with {'file': file} %}
As #walther pointed out in comments, it is not actually required to pass variables since an included template get access to variables of the active context, i.e. you can simply write:
{% include 'NaSoftEdmBundle:Contractor:file.html.twig' %}
and the file variable will be used.
You still have to use the with syntax if you want to assign a new variable, e.g.
{% include 'NaSoftEdmBundle:Contractor:files.html.twig' with {'files': form.files} %}
See http://twig.sensiolabs.org/doc/tags/include.html