Using Django's cached template loader causes an exception in the templates panel

[kezabelle]

Given:

TEMPLATE_LOADERS = (
    ('django.template.loaders.cached.Loader', (
        'django.template.loaders.filesystem.Loader',
        'django.template.loaders.app_directories.Loader',
    )),
)

• Open a page which shows djdt
• Open the templates panel (obviously, this panel needs to be enabled)
• Try and view one of the templates used.
• You should receive a 500 ISE.

NotImplementedError at /__debug__/template_source/
subclasses of BaseLoader must provide a load_template_source() method
Django Version: 1.7.1
Python Version: 2.7.6
Traceback:
File "/SITE_PACKAGES/django/core/handlers/base.py" in get_response
  111.                     response = wrapped_callback(request, *callback_args, **callback_kwargs)
File "/SITE_PACKAGES/debug_toolbar/panels/templates/views.py" in template_source
  27.             source, display_name = loader.load_template_source(template_name)
File "/SITE_PACKAGES/django/template/loader.py" in load_template_source
  65.         raise NotImplementedError('subclasses of BaseLoader must provide a load_template_source() method')

Which makes some amount of sense, as the caching Loader doesn't implement load_template_source (arguably upstream could make a change to provide one, though, possibly by just re-calling find_template)

There may very well be nothing that can done in djdt, but I couldn't see any documentation caveats that explain as much (having searched RTD and google), and it was a bit confusing, given that the template panel appeared to work fine -- showed the correct templates used, etc.

[tim-schilling]

Thanks for the bug report. The toolbar replicates part of Django's logic for getting the source of a template, but it didn't handle the slight difference of the cached template loader.