Template Debug highlights wrong {% for %} tag

[Charmless <jim-django@…>]

When an exception happens within a for tag's head, the error source is assigned always assigned to the top-level for loop, even if the erroneous for tag is nested.

Example:

{% for a in as %}
  {% for b in a.bs %}
    {% for c in b.relatedobject_set %}
       {{ c.foo }}
    {% endfor %}
  {% endfor %}
{% endfor %}

The error here is at "b.relatedobject_set", which should be "b.relatedobject_set.all" (assuming b is a model related to a model releatedobject).

As is, the template debug system marks the top level for tag, "{% for a in as %}", as being the point of error. The correct place to mark is the for tag where the error happened.

Attached is a patch that fixes this. I'm not familiar with Django's tag tests, so I can't include any, but would be happy to learn and supply some if it is agreed that this is a correct fix.

[Charmless <jim-django@…>]

patch against SVN revision 6626

[Gary Wilson]

#6468 marked as a dup. It also has a template example that shows the bug.

[Julien Phalip]

Confirming that this issue is still occurring. Needs tests to take this further. The patch also needs improvement as the ForNode's code has changed since 4 years ago.

[Vladimir Moskva]

django.template.defaulttags.ForNode.render method calls .render method for subnodes and there loses the information which exactly node caused the error, that's why DebugNodeList always marked the first forloop of nested as which caused the error.

I've made a patch which adds source of the the node that actually caused the error as the exception's attribute, which is later intercepted by DebugNodeList.render method.

Tests are included.

[Vladimir Moskva]

Chanded order if and try..except statements. Now try..except is performed only when settings.TEMPLATE_DEBUG is true, so it shouldn't slower rendering with debugger disabled.

[Vladimir Moskva]

Chanded order if and try..except statements. Now try..except is performed only when settings.TEMPLATE_DEBUG is true, so it shouldn't slower rendering with debugger disabled.

[Vladimir Moskva]

Fixed typo in a comment

[Jannis Leidel]

In [16605]:

Fixed #5831 -- Made sure the ForNode reports the correct source of an exception happening in one of the loops. Thanks, Charmless and vladmos.