RFC: Arbitrary variables as nested content

[koterpillar]

Motivation

I have the following widgets (simplified for brevity):

{% block _label %}
  <label for="{{ id_for_label }}">{{ label }}</label>
{% endblock %}

{% block CharField %}
  {% reuse _label %}
  <input id="{{ id_for_label }}" type="text">
{% endblock %}

For a particular use case, I want to generate the following:

<label for="id_my_field">Customized <a href="/somewhere">HTML</a> label</label>
<input id="id_my_field" type="text">

Where /somewhere is a result of reverse('some_view').

The hacky solution is set the label of the form field to the HTML and mark it safe. However, due to circular imports and mark_safe not playing along with reverse_lazy this isn't feasible, and besides, HTML belongs in the templates.

Solution

Sniplates has nested_widget, but it forces the variable name to be content, not label, and doesn't have the automatic attribute extraction of the form_field.

Mild option

{% form_field my_field nested_content_for='label' %}
  Customized {% url 'some_view' %} label
{% end_form_field %}

Upon seeing nested_content_for, form_field parses the inside content and assigns the result to label in the context. widget works the same. nested_widget is deprecated as it is equivalent to {% widget nested_content_for='content' %}.

If nested_content_for is not specified as an argument for form_field or widget, they behave like now.

Crazy option

{% form_field my_field nested %}
{% attribute 'label' %}
  Customized {% url 'some_view' %} label
{% attribute 'something_else' %}
  Multiple parameters can be specified!
{% end_form_field %}

Upon seeing nested as an attribute, form_field (and widget) look for {% attribute ... %} sections and add their result to the context. The advantage over the first option is the ability to specify multiple inline arguments.

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I'm not particularly attached to the wording, etc. If you're okay with either option, I can write up a PR.

[funkybob]

Why can't you use {% url %} to get the lookup of the url?

Also, if this is the same problem you were having the other day, why must it be a lazy reverse? Why not do the reverse in the Form init?

[koterpillar]

I can put label in __init__, but that still leaves a chunk of HTML in the Python file. I never said I couldn't use {% url %}, though.

[koterpillar]

I don't remember why I needed this anymore...