Using the flatten filter in scripts and rest sensors causes them to break after a restart

[philipdouglas]

I was very excited when I discovered Spook because I have so many times found myself reaching for a flatten filter that didn't exist when writing HA templates. I've started using it in various places and run into problems when I restart home assistant.

I tried using it in a restful sensor's value_template but I get an error when HA starts because it cannot find the flatten filter which then disables the sensor.

Similarly, I am using it in a script, but it also gets disabled after a restart because the filter isn't recognised. I can workaround this by tweaking the script and saving it, but it's annoying to have to do that after every restart.

Is there either a way to force spook to load before these other integrations, or to change the templates to fail more gracefully when flatten hasn't loaded yet?

Thanks in advance for any suggestions!

[philipdouglas]

After writing the above, I discovered the is filter test (https://jinja.palletsprojects.com/en/3.1.x/templates/#jinja-tests.filter) which seemed to do what I want. However, despite it working as I'd expect in the dev tools, when I use it in a rest sensor, it seems to always fail:

        value_template:  >-
          {% if "flatten" is filter %}
            {{ value_json.data.category_groups | map(attribute="categories") | flatten(levels=1) | selectattr("balance", "lt", 0) | list | length }}'
          {% else %}
            unavailable
          {% endif %}

Even well after a restart, this sensor is stuck as "unavailable".