Currently if you want to use inline bootstrap form rendering, this is usually

enough:

1. Using bootstrap_3_layout.html.twig
2. Rendering form with `{{ form(form, { 'attr': {'class': 'form-inline'} }) }}`

Form rendering breaks for buttons as the buttons are rendered in a separate
<div> element without any attributes (this is coming from
form_div_layout.html.twig which has this block hard-coded). The rest of the
elements render with <div class="form-group"> which make them compatible with
form-inline attribute in the form (`<form class="form-inline">`).

The problem makes buttons render on new lines for inline forms. Extending
button_row in bootstrap_3_layout.html.twig template fixes this.

Signed-off-by: Edvinas Klovas <edvinas@pnd.io>

src/Symfony/Bridge/Twig/Resources/views/Form/bootstrap_3_layout.html.twig

@@ -181,6 +181,12 @@
     </div>
 {%- endblock form_row %}
 
+{% block button_row -%}
+    <div class="form-group">
+        {{- form_widget(form) -}}
+    </div>
+{%- endblock button_row %}
+
 {% block choice_row -%}
     {% set force_error = true %}
     {{ block('form_row') }}