dj-angles doesn't seem to play well with missing template context variables

[joshuadavidthomas]

Okay, so I'm starting this discussion primarily to track me trying to debug this issue. The title is a hypothesis, I'm not totally sure what's going on TBH, but it does seem to involve something with dj-angles.

I installed and configured dj-angles on one of our projects at work and immediately one of the views I was working on refused to load. It's a view that contains a couple of django-tables2 tables (one big one, with a bunch of sub-tables on each row) and a django-bird component for modals on each of the rows. The template is pretty standard, with if checks for context variables that may exist and if they don't fall back to the else, for example here's the table header:

          {% if table.show_header %}
            <thead class="text-sm font-semibold text-left text-gray-900 bg-gray-100 bg-opacity-75 border-b border-gray-300 border-t-[0.5px] backdrop-blur backdrop-filter"
                   {{ table.attrs.thead.as_html }}>
              <tr>
                {% for column in table.columns %}
                  <th scope="col"
                      class="py-3.5 {% if forloop.first %}pr-3 pl-4 sm:pl-6 lg:pl-8{% elif forloop.last %}pl-3 pr-4 sm:pr-6 lg:pr-8{% else %}px-3{% endif %}{% if column.attrs.right_align %} text-right{% endif %}"
                      data-column="{{ column.name }}"
                      {{ column.attrs.th.as_html }}>
                    {% if column.orderable %}
                      <a href="{% querystring table.prefixed_order_by_field=column.order_by_alias.next %}"
                         class="inline-flex items-center hover:underline group">
                        {{ column.header }}
                        {% if column.is_ordered %}
                          <span class="flex-none ml-2 text-gray-900 bg-gray-200 rounded group-hover:bg-gray-300">
                            {% if column.order_by_alias|startswith:'-' %}
                              {% heroicon_mini "chevron-up" size=16 %}
                            {% else %}
                              {% heroicon_mini "chevron-down" size=16 %}
                            {% endif %}
                          </span>
                        {% endif %}
                      </a>
                    {% else %}
                      {{ column.header }}
                    {% endif %}
                  </th>
                {% endfor %}
              </tr>
            </thead>
          {% endif %}

When attempting to load this view, the browser just spins and never resolves while the development server logs show nothing. Enabling DEBUG logging helped, as it starts to output logs like this:

app-1  | 2025-02-05 08:58:00,042 django.template DEBUG    Exception while resolving variable 'right_align' in template 'django_twc_ui/tables/select_table.html'.
app-1  | Traceback (most recent call last):
app-1  |   File "/usr/local/lib/python3.12/site-packages/django/template/base.py", line 883, in _resolve_lookup
app-1  |     current = current[bit]
app-1  |               ~~~~~~~^^^^^
app-1  | KeyError: 'right_align'
app-1  | 
app-1  | During handling of the above exception, another exception occurred:
app-1  | 
app-1  | Traceback (most recent call last):
app-1  |   File "/usr/local/lib/python3.12/site-packages/django/template/base.py", line 893, in _resolve_lookup
app-1  |     current = getattr(current, bit)
app-1  |               ^^^^^^^^^^^^^^^^^^^^^
app-1  | AttributeError: 'dict' object has no attribute 'right_align'
app-1  | 
app-1  | During handling of the above exception, another exception occurred:
app-1  | 
app-1  | Traceback (most recent call last):
app-1  |   File "/usr/local/lib/python3.12/site-packages/django/template/base.py", line 899, in _resolve_lookup
app-1  |     current = current[int(bit)]
app-1  |                       ^^^^^^^^
app-1  | ValueError: invalid literal for int() with base 10: 'right_align'
app-1  | 
app-1  | During handling of the above exception, another exception occurred:
app-1  | 
app-1  | Traceback (most recent call last):
app-1  |   File "/usr/local/lib/python3.12/site-packages/django/template/base.py", line 906, in _resolve_lookup
app-1  |     raise VariableDoesNotExist(
app-1  | django.template.base.VariableDoesNotExist: Failed lookup for key [right_align] in {'thead': AttributeDict(), 'tbody': AttributeDict(), 'tfoot': AttributeDict(), 'th': AttributeDict({'class': 'orderable'}), 'td': AttributeDict({'class': None}), 'tf': AttributeDict({'class': None})}

I'm only including a small portion of the logs related to what I think is happening with the above table header snippet. There's actually a log entry for all of the undefined variables in the template.

This seems to be related to this portion of the table header:

{% if column.attrs.right_align %} text-right{% endif %}

What ends up happening is an endless loop, where browser is continuously loading and the logs keep scrolling past showing the same logs as seen above, over and over again on repeat.

If I remove dj_angles.template_loader.Loader from the list of template loaders, the problem goes away -- the logs show the VariableDoesNotExist error logs, but just once and the browser is able to load the page just fine.

[joshuadavidthomas]

I'll try and get a minimum repro here soon (or even better, a unit test or two), I wanted to capture this asap while I was working through it.

[adamghill]

I do similar things in my templates where variables might be missing sometimes. Just tried a simple example that I put a screenshot of below. The top is a regular template with <dj-movie-carousel />; the the bottom is the partial movie-carousel.html where I put in {% if missing_variable %} which seems to work as expected. I think I'm missing something here!

[joshuadavidthomas]

Yeah, I'm not totally convinced it's not just user error on my part and that something about that project's configuration is not quite right. The error logs only appearing when the dj-angles loader is there could be a red herring pointing me in the wrong direction.

That's why I wanted to try and get a minimal reproduction, but I've been up against a deadline and haven't had a chance to pick this back up yet.

Thanks for trying though. ☺️ I wouldn't waste anymore time on it until I can get to the bottom of this.

[adamghill]

Thanks for the initial discussion! If you can reproduce it, that would be great.

I have noticed that dj-angles chokes on newlines in some places so long lists of tailwind classes + VS Code reformatting my HTML causes some problems. Not sure if that is what is happening here or not, though.

[adamghill]

Looking at your code, I'm guessing the newline issue isn't the problem. But, I just pushed 0.13.0 with that change just in case.