Config Template rendering: templating with 100% more guesswork

[pobk]

Writing Jinja2 templates for config rendering in NetBox is a magical experience.

You add some contexts, throw a few {% if %} statements, maybe nest some includes... Open the preview and bam! Either:

1. You get a full-blown NetBox exception that looks like it escaped from the ninth circle of Django hell, or
2. A vague template rendering error, message that helpfully tells you nothing, or where it is, even when it's 14 levels deep in an include you wrote 2 years ago, and have completely forgotten about.

No line-numbers. No traceback. Just a quiet sense of shame and an afternoon of tears and regret, the likes of which drives you to crack open a botle of whisky at 9am on a Wednesday because it's going to be "One of those days".

I'm proposing a change to the rendering process:

• Add "debug mode" flag to the ConfigTemplate objects.
• When enabled, ConfigTemplates should gracefully handle and render errors and include any tracebacks, template info... dare we dream offending line-numbers?
• Stretch goal, include the Jinja environment variables used in the template - perhaps the output similar to the debug extension and {% debug %} tag.

Right now, debugging config templates feels like building IKEA furniture blinefolded, with the instructions printed in Base64.

Not having NetBox blow-up with an unhandled exception would really help as a starter for 10.

~ R

[jnovinger]

@pobk , I think this could be a significant quality-of-life improvement for writing config templates. Some things to keep in mind as you craft the FR:

• Templates show up in multiple places in NetBox, it would be great if this work could cover all the places.
• Propose specific changes and give at (the very) least what an implementation might look like.
• Include real-life pain points in your Use Case section, if at all possible. If you need to redact things, no problem, but help the reviewer understand the real need for this feature.
• Given that user-level templating is built on Jinja2, are there existing tools/patterns in Jinja that could help achieve your goal? What about other template editing experiences do you like from other projects that might help achieve the goal?
• Keep the humor, I love it.

Looking forward to seeing this FR!