Document that {% include %} suppresses errors when DEBUG=False

[Pratyush Mittal]

It seems that the TemplateDoesNotExist error is not raised in Django 1.8 tests. Adding {% include "MissingTemplate.html" %} in templates will pass the tests without an error, though it will raise an error on manual browsing.

Demo Code: ​https://github.com/pratyushmittal/DummyProject

I have provided an example testcase above. In the DummyProject, running python manage.py test should pass the tests, while python manage.py runserver and opening 127.0.0.1:8000 should raise a TemplateDoesNotExist error.

[Andriy Sokolovskiy]

Checked on built-in django template engine, error is not rising.
Got TemplateNotFound on jinja2.

Seems to be a bug.

[Pratyush Mittal]

It seems that include template tag is altogether being skipped in the tests in Django 1.8.

[Tim Graham]

Django tests run with DEBUG=False. In this case, template tag exceptions are often suppressed. It might be worth adding a note to ​the {% include %} documentation that the tag ​will render as an empty string if rendering the included template raises an exception.

[Andriy Sokolovskiy]

In this case, template tag exceptions are often suppressed

Seems that other template engines should have the same behaviour.

[Tim Graham]

I'm not sure what you have in mind, but it doesn't make sense to me that we can enforce design decisions of the Django template language onto other templating languages. In particular, the relevant documentation can be found in the ​custom template tags docs:

render() should generally fail silently, particularly in a production environment. In some cases however, particularly if context.template.engine.debug is True, this method may raise an exception to make debugging easier. For example, several core tags raise django.template.TemplateSyntaxError if they receive the wrong number or type of arguments.

[Tim Graham]

​PR (with comments for improvement).

[Tim Graham <timograham@…>]

In fc3409b0:

Fixed #24813 -- Documented {% include %} debug behavior variance

[Tim Graham <timograham@…>]

In 5a0e39b:

[1.8.x] Fixed #24813 -- Documented {% include %} debug behavior variance

Backport of fc3409b0932959f2aca42715e9147113d0e40f79 from master