{% if "x"|length_is:n %} always evaluates True

[Thomas Steinacher <tom@…>]

{% if "x"|capfirst|length_is:n %} is always true. Example:

In [1]: from django.template import Template, Context

In [2]: Template('{% if "x"|capfirst|length_is:0 %}This is wrong{% endif %}').render(Context({}))
Out[2]: u'This is wrong'

Using latest Django SVN.

[Carl Meyer]

capfirst is irrelevant. This also fails:

>>> Template('{% if "x"|length_is:0 %}Wrong{% endif %}').render(Context({}))
u'Wrong'

Changed summary to reflect this. Also changed version to SVN, as this problem is still present in trunk.

The problem here is that the is_safe attribute is set on the length_is tag, which causes mark_safe to be called on the return value, and mark_safe(False) returns the string 'False'. Not sure where in that chain is the proper place for the fix. It's possible that mark_safe needs to be smart about not always coercing its argument to a string, or FilterExpression.resolve needs to check if the return value is a string before calling mark_safe on it. But the naive fix is just to remove the is_safe attribute from length_is, since auto-escaping will never harm its return value.

[Carl Meyer]

failing test

[Carl Meyer]

simple fix (remove is_safe from length_is filter)

[Chris Beaven]

Removal of is_safe is the right thing to do. It's a gotcha though -- a note explaining that is_safe shouldn't be used if you're relying on a non-string return object in docs/howto/custom-template-tags.txt would be useful.

[Carl Meyer]

same patch, with warning note in docs

[Karen Tracey]

(In [9291]) Fixed #8966 -- Changed is_safe for length_is filter to False, since its return value is a boolean, not a string.

Thanks Thomas Steinacher and carljm.

[Karen Tracey]

(In [9292]) [1.0.X] Fixed #8966 -- Changed is_safe for length_is filter to False, since its return value is a boolean, not a string.

Thanks Thomas Steinacher, carljm, and SmileyChris.

Backport of r9291 from trunk.