firstof template tag documentation incorrectly specifies value testing.

[Keryn Knight]

The documentation for {%firstof x y z %} says:

Outputs the first argument variable that is not False. Outputs nothing if all the passed variables are False.

The emphasis not mine, and indicates it's specifically testing for the singleton False. But the example it gives as an equivalent is based on normal ​truth value testing:

{% if var1 %}
    {{ var1 }}
{% elif var2 %}
    {{ var2 }}
{% elif var3 %}
    {{ var3 }}
{% endif %}

and the ​code is also based on truthiness

The documentation for how a simple {% if ... %} behaves meanwhile more correctly prescribes it's function related to "true" and what that means.

evaluates a variable, and if that variable is “true” (i.e. exists, is not empty, and is not a false boolean value) the contents of the block are output

Were it actually based on False rather than Falsiness, the following would not output truthy.

>>> from django.template import Template, Context
>>> context = {'a': None,'b': False,'c': 0,'d': '','e': (),'f': [],'g': {},'h': set(),'i': "truthy"}
>>> t = Template("{% firstof a b c d e f g h i %}")
>>> t.render(Context(context))
'truthy'

Suggestion is to clarify that it's based on truthiness/falsiness, rather than imply it's directly based on encountering False.

[Uttam Kini]

Pull request: ​https://github.com/django/django/pull/12162

[Mariusz Felisiak <felisiak.mariusz@…>]

In 84936ac2:

[3.0.x] Fixed #31024 -- Clarified {% firstof %} tag's handling of arguments.

Backport of d646e3d14fa04b5081476b84f4500c8651c167c2 from master

[Mariusz Felisiak <felisiak.mariusz@…>]

In d646e3d:

Fixed #31024 -- Clarified {% firstof %} tag's handling of arguments.