title: How can I find the file that's causing a Django error? Getting "Invalid filter: 'add_class'" but no file
body: <p>So the site itself runs without any errors that I can find.</p>
  
  <p>I have shrink installed and I'm trying to run collect static.  In the process of running it gives me a TemplateSyntaxError.  Every file in the traceback is a site-package file and I'm not sure how to go about finding where the error is coming from.  Are there any tools that will check that and let me see where/how it's processing so I can perhaps have a way to find where the error is coming from?</p>
  
  <p>This is my traceback:</p>
  
  <pre><code>&gt; You have requested to collect static files at the destination location
  &gt; as specified in your settings.
  &gt; 
  &gt; This will overwrite existing files! Are you sure you want to do this?
  &gt; 
  &gt; Type 'yes' to continue, or 'no' to cancel: yes
  &gt; 
  &gt; 0 static files copied, 1249 unmodified. Traceback (most recent call
  &gt; last):   File "tools/manage.py", line 16, in &lt;module&gt;
  &gt;     execute_manager(settings)   File "/home/adam/pyprojects/trekadoo-web/venv/local/lib/python2.7/site-packages/django/core/management/__init__.py",
  &gt; line 459, in execute_manager
  &gt;     utility.execute()   File "/home/adam/pyprojects/trekadoo-web/venv/local/lib/python2.7/site-packages/django/core/management/__init__.py",
  &gt; line 382, in execute
  &gt;     self.fetch_command(subcommand).run_from_argv(self.argv)   File "/home/adam/pyprojects/trekadoo-web/venv/local/lib/python2.7/site-packages/django/core/management/base.py",
  &gt; line 196, in run_from_argv
  &gt;     self.execute(*args, **options.__dict__)   File "/home/adam/pyprojects/trekadoo-web/venv/local/lib/python2.7/site-packages/django/core/management/base.py",
  &gt; line 232, in execute
  &gt;     output = self.handle(*args, **options)   File "/home/adam/pyprojects/trekadoo-web/venv/local/lib/python2.7/site-packages/django/core/management/base.py",
  &gt; line 371, in handle
  &gt;     return self.handle_noargs(**options)   File "/home/adam/pyprojects/trekadoo-web/venv/local/lib/python2.7/site-packages/shrink/management/commands/collectstatic.py",
  &gt; line 58, in handle_noargs
  &gt;     templates.add(get_template(pjoin(dirpath, f)))   File "/home/adam/pyprojects/trekadoo-web/venv/local/lib/python2.7/site-packages/django/template/loader.py",
  &gt; line 145, in get_template
  &gt;     template, origin = find_template(template_name)   File "/home/adam/pyprojects/trekadoo-web/venv/local/lib/python2.7/site-packages/django/template/loader.py",
  &gt; line 134, in find_template
  &gt;     source, display_name = loader(name, dirs)   File "/home/adam/pyprojects/trekadoo-web/venv/local/lib/python2.7/site-packages/django/template/loader.py",
  &gt; line 42, in __call__
  &gt;     return self.load_template(template_name, template_dirs)   File "/home/adam/pyprojects/trekadoo-web/venv/local/lib/python2.7/site-packages/django/template/loader.py",
  &gt; line 48, in load_template
  &gt;     template = get_template_from_string(source, origin, template_name)   File
  &gt; "/home/adam/pyprojects/trekadoo-web/venv/local/lib/python2.7/site-packages/django/template/loader.py",
  &gt; line 156, in get_template_from_string
  &gt;     return Template(source, origin, name)   File "/home/adam/pyprojects/trekadoo-web/venv/local/lib/python2.7/site-packages/django/template/base.py",
  &gt; line 125, in __init__
  &gt;     self.nodelist = compile_string(template_string, origin)   File "/home/adam/pyprojects/trekadoo-web/venv/local/lib/python2.7/site-packages/django/template/base.py",
  &gt; line 153, in compile_string
  &gt;     return parser.parse()   File "/home/adam/pyprojects/trekadoo-web/venv/local/lib/python2.7/site-packages/django/template/base.py",
  &gt; line 267, in parse
  &gt;     compiled_result = compile_func(self, token)   File "/home/adam/pyprojects/trekadoo-web/venv/local/lib/python2.7/site-packages/django/template/loader_tags.py",
  &gt; line 214, in do_extends
  &gt;     nodelist = parser.parse()   File "/home/adam/pyprojects/trekadoo-web/venv/local/lib/python2.7/site-packages/django/template/base.py",
  &gt; line 267, in parse
  &gt;     compiled_result = compile_func(self, token)   File "/home/adam/pyprojects/trekadoo-web/venv/local/lib/python2.7/site-packages/django/template/loader_tags.py",
  &gt; line 189, in do_block
  &gt;     nodelist = parser.parse(('endblock',))   File "/home/adam/pyprojects/trekadoo-web/venv/local/lib/python2.7/site-packages/django/template/base.py",
  &gt; line 246, in parse
  &gt;     filter_expression = self.compile_filter(token.contents)   File "/home/adam/pyprojects/trekadoo-web/venv/local/lib/python2.7/site-packages/django/template/base.py",
  &gt; line 346, in compile_filter
  &gt;     return FilterExpression(token, self)   File "/home/adam/pyprojects/trekadoo-web/venv/local/lib/python2.7/site-packages/django/template/base.py",
  &gt; line 557, in __init__
  &gt;     filter_func = parser.find_filter(filter_name)   File "/home/adam/pyprojects/trekadoo-web/venv/local/lib/python2.7/site-packages/django/template/base.py",
  &gt; line 352, in find_filter
  &gt;     raise TemplateSyntaxError("Invalid filter: '%s'" % filter_name) django.template.base.TemplateSyntaxError: Invalid filter: 'add_class'
  </code></pre>
  
  <p>add_class is used hundreds of time throughout the project.</p>