Subwidgets not passed required and disabled attributes in BoundField.__iter__()

[Jon Dufresne]

Similar in spirit to #20555.

I have a form with a field like:

my_field = forms.ChoiceField(widget=forms.RadioSelect, choice=get_choices(), disabled=True)

The field's radio buttons are rendered in a template by iterating over the BoundField:

{% for choice in form.my_field %}
  {{ choice.tag }}
{% endfor %}

The rendered HTML input is not disabled. This is because ​BoundField.__iter__() does not pass the required and disabled attributes to subwidgets.

Contrast this with ​BoundField.as_widget() where the values are passed.

Perhaps this attribute building should be factored to a utility function out and shared across these two functions.

[Jon Dufresne]

​PR

I think this PR, or at least parts of it, should be considered for 1.10. The required attribute is newly introduced in 1.10 with the following concerns:

1. The ​documentation about looping over subwidgets suggests the required attribute will be carried over during iteration. (From this one might also assume disabled.)
2. IMO more importantly, as noted in the PR, the CheckboxSelectMultiple widget will behave incorrectly with the required attribute. When browsers see multiple checkboxes with the same name attribute marked required the browser requires all checkboxes checked instead of at least one. This validation contradicts Django's server side validation of requiring at least one item for multiple choice fields. This will make Django forms using CheckboxSelectMultiple appear broken.

[Tim Graham <timograham@…>]

In ac3aaaa:

Fixed #26927 -- Made subwidget iteration pass disabled and required attributes.

[Tim Graham <timograham@…>]

In 6a3f31fa:

[1.10.x] Fixed #26927 -- Made subwidget iteration pass disabled and required attributes.

Backport of ac3aaaa740dcf9c6efd2f88ee9219c1924c7695e from master