A numerical value of 0 is incorrectly treated as falsy

[latimer1]

Per https://shopify.github.io/liquid/basics/truthy-and-falsy/ "All values in Liquid are truthy except nil and false."

However, the integer 0 and float 0.0 are being treated as falsy.

Trying the following code input:

{% if 0.0 %} 0.0 float {% endif %}
{% if 0 %} 0 int {% endif %}
{% if '0' %} 0 string {% endif %}

Output:

0 string

If this is intended, I don't see this boolean behavior defined in known issues in https://jg-rp.github.io/liquid/known_issues

[latimer1]

The issue is https://github.com/jg-rp/liquid/blob/main/liquid/expression.py#L914

obj in (False, None) evaluates to true because 0.0 == False is True.

[jg-rp]

Hi @latimer1,

I believe the case of {% if 0 %}... was fixed in version 1.4.2 with #65, but I hadn't considered {% if 0.0 %}..., so that's defiantly a bug that needs fixing.

Expected output from your example:

 0.0 float 
 0 int 
 0 string

Thanks for letting me know.

[latimer1]

I wonder if adding a type check would address any edge cases.

if type(obj) == type(False) and obj == False:
   return False
if type(obj) == type(None) and obj == None:
   return False

[jg-rp]

There are a couple of cases that that does not cover. Undefined variables and drops that define __bool__ or __int__ methods can be falsy too.

This bug also extends to comparison operators and the default filter:

{% if 0.0 == false %}0.0 == false{% endif %}
{{ 0.0 | default: "hello" }}

Expected output

0.0

Actual output

0.0 == false 
hello

[jg-rp]

Fixed in version 1.4.5, now released.