CrispyFieldNode’s attribute expansion is overly strict

[interDist]

• Package version: 1.12.0
• Django version: 2.2.25

Description

The template tag {% crispy_field %} allows setting additional attributes to be rendered on the HTML tag. The expansion / resolving of the values is restricted to a variable defined in the template’s context and does not allow using filters.
This is due to the usage of template.Variable, while template.FilterExpression should have been used.

Example code:

{% crispy_field field "data-question" var_q|default_if_none:"?" %}

Expected

The resulting HTML page includes an <input> tag with data-question="?" attribute if var_q is None and with data-question="how?" attribute if var_q is "how?".

Actual behavior

The following template error:

VariableDoesNotExist

Failed lookup for key [var_q|default_if_none:"?"] in context.

Offending lines: https://github.com/django-crispy-forms/django-crispy-forms/blob/1.12.0/crispy_forms/templatetags/crispy_forms_field.py#L150-L153