Add build number display based on git information.

mayan/apps/appearance/templates/appearance/about.html

@@ -58,8 +58,12 @@
     <h3>{% trans 'About' %}</h3>
     <hr>
 
+    {% build as build_number %}
     <div class="well">
         <h3 class="text-center">{% project_name %} ({% trans 'Version' %} {% project_version %})</h3>
+        {% if build_number %}
+            <p class='text-center'>{% blocktrans with build_number as build_number %}Build number: {{ build_number }}{% endblocktrans %}</p>
+        {% endif %}
         <p class="text-center">
             {% project_description as project_description %}
             {% trans project_description %}

mayan/apps/common/templatetags/common_tags.py

@@ -2,6 +2,8 @@ from __future__ import unicode_literals
 
 from json import dumps
 
+import sh
+
 from django.conf import settings
 from django.template import Context, Library
 from django.template.loader import get_template
@@ -12,6 +14,14 @@ from ..utils import return_attrib
 
 register = Library()
 
+try:
+    BUILD = sh.Command('git').bake('describe', '--tags', '--always', 'HEAD')
+    DATE = sh.Command('git').bake('--no-pager', 'log', '-1', '--format=%cd')
+except sh.CommandNotFound:
+    logger.debug('git not found')
+    BUILD = None
+    DATE = None
+
 
 @register.filter
 def get_encoded_parameter(item, parameters_dict):
@@ -61,3 +71,11 @@ def render_subtemplate(context, template_name, template_context):
     new_context = Context(context)
     new_context.update(Context(template_context))
     return get_template(template_name).render(new_context)
+
+
+@register.assignment_tag
+def build():
+    if BUILD:
+        return '{} {}'.format(BUILD(), DATE().decode())
+    else:
+        return 'No build information'