#16147: {% include %} tag raises TemplateDoesNotExist at compile time of parent
template if TEMPLATE_DEBUG is True
-------------------------------------------------+-------------------------
Reporter: mrmachine | Owner: nobody
Type: Bug | Status: new
Milestone: 1.4 | Component:
Version: 1.3 | Template system
Keywords: include template | Severity: Normal
TemplateDoesNotExist TEMPLATE_DEBUG | Triage Stage:
Has patch: 0 | Unreviewed
| Easy pickings: 0
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I think this is a bug. Or at the very least, it can make for unexpected
behaviour that is difficult to trace. When developing locally, `DEBUG` and
`TEMPLATE_DEBUG` are often `True`. When `TEMPLATE_DEBUG` is `True`,
compiling a template that contains an `{% include %}` to a template that
doesn't exist will raise `TemplateDoesNotExist` at compile time of the
parent template.
{{{
>>> from django.template import Template
>>> t = Template('{% include "missing.html" %}')
Traceback (most recent call last):
...
TemplateDoesNotExist: missing.html
}}}
The problem is that when you try to conditionally load a template, and
perform a different action if it does not exist. For example, you might
have a view that uses `select_template` to load one of several templates
(if one exists) and send an email. If no email was sent (because no
template exists), render a different template/context to the response or
take some other action. If the email template contains a typo in the name
of an included template, the email template will not be loaded and no
email will be sent because `TemplateDoesNotExist` was raised.
In the local dev environment, this will not display a pretty debug page
showing the error inside the email template, it will simply behave
unexpectedly (by not sending an email when the email template DOES exist).
On the production server (or when `TEMPLATE_DEBUG` is `False`), it will
behave as expected. The email template will be found and it will be
rendered.
This problem doesn't exist when using a variable as the template name.
{{{
>>> t = Template('{% include somevar %}')
>>>
}}}
Why does Django try to execute the `{% include %}` when it contains a hard
coded string at compile time at all? I think this is a case of premature
optimisation. If it execution of the `{% include %}` was delayed until
render time, `select_template` would correctly return the email template
when `TEMPLATE_DEBUG` is `True`, and the proper error would be displayed
in the rendered email template (making it an easy fix to correct the
typo).
--
Ticket URL: <https://code.djangoproject.com/ticket/16147>
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