Admin radio_fields have an invalid aria-describedby attribute.

[David Smith]

#35892 added support for Widget.use_fieldset in admin forms. Refs 4187da258fe212d494cb578a0bc2b52c4979ab95

An incorrect aria-describedby attribute is generated for radio_fields with help_text and no reference is available for errors.

Given this form:

class Colour(models.Model):
    name = models.CharField(max_length=100, help_text='Enter your name')

    COLOUR_CHOICES = [
        ('red', 'Red'),
        ('green', 'Green'),
        ('blue', 'Blue'),]

    favourite_colour = models.CharField(
        max_length=10,
        choices=COLOUR_CHOICES,
        help_text='Colour of the favourite colour',
    )

... and model admin:

class ColourAdmin(admin.ModelAdmin):
    radio_fields = {"favourite_colour": admin.VERTICAL}
    model = Colour

Adding a new Colour record in the admin with no inputs gives the following HTML for the favourite_colour field.

Notice how the aria-describedby in the <fieldset> is _helptext. This id does not exist, and also there is no reference to "id_favourite_colour_error" to reference the error list.

<fieldset aria-describedby="_helptext">
    <legend class="required">Favourite colour:</legend>
    <div class="flex-container errors">
        <div class="help">
            <div>Colour of the favourite colour</div>
        </div>

        <ul class="errorlist" id="id_favourite_colour_error">
            <li>This field is required.</li>
        </ul>

        <div id="id_favourite_colour" class="radiolist">
            <div>
                <label for="id_favourite_colour_0">
                    <input type="radio" name="favourite_colour" value="red" class="radiolist" required="" aria-invalid="true" id="id_favourite_colour_0" /> Red
                </label>
            </div>
            <div>
                <label for="id_favourite_colour_1">
                    <input type="radio" name="favourite_colour" value="green" class="radiolist" required="" aria-invalid="true" id="id_favourite_colour_1" /> Green
                </label>
            </div>
            <div>
                <label for="id_favourite_colour_2">
                    <input type="radio" name="favourite_colour" value="blue" class="radiolist" required="" aria-invalid="true" id="id_favourite_colour_2" /> Blue
                </label>
            </div>
        </div>
    </div>
</fieldset>

Contrast that to the name field where both the help_text and errors have a valid aria-describedby references from the <input>.

Using aria-describedby from the field's boundfield (field.field in this case) is where I'd be looking to fix the issue.

django/contrib/admin/templates/admin/includes/fieldset.html

@@ -10 +10 @@
     {% for line in fieldset %}
         <div class="form-row{% if not line.fields|length == 1 %} flex-container form-multiline{% endif %}{% if not line.has_visible_field %} hidden{% endif %}{% for field in line %}{% if field.field.name %} field-{{ field.field.name }}{% endif %}{% endfor %}">
             {% for field in line %}
-                {% if field.is_fieldset %}<fieldset{% if field.field.help_text %} aria-describedby="{{ field.field.id_for_label }}_helptext"{% endif %}>{{ field.label_tag }}{% endif %}
+                {% if field.is_fieldset %}<fieldset{% if field.field.aria_describedby %} aria-describedby="{{ field.field.aria_describedby }}"{% endif %}>{{ field.label_tag }}{% endif %}
                 <div class="flex-container{% if not field.is_readonly and field.errors or line.fields|length == 1 and line.errors %} errors{% endif %}{% if not line.fields|length == 1 %} fieldBox{% if field.field.name %} field-{{ field.field.name }}{% endif %}{% if field.field.is_hidden %} hidden{% endif %}{% endif %}{% if field.is_checkbox %} checkbox-row{% endif %}">
                     {% if field.is_checkbox %}
                         <div class="checkbox">
@@ -21 +21 @@
                         {% if not field.is_fieldset %}{{ field.label_tag }}{% endif %}
                     {% endif %}
                     {% if field.field.help_text %}
-                        <div class="help{% if field.field.is_hidden %} hidden{% endif %}"{% if field.field.id_for_label %} id="{{ field.field.id_for_label }}_helptext"{% endif %}>
+                        <div class="help{% if field.field.is_hidden %} hidden{% endif %}"{% if field.field.auto_id %} id="{{ field.field.auto_id }}_helptext"{% endif %}>
                             <div>{{ field.field.help_text|safe }}</div>
                         </div>
                     {% endif %}

Then for tests I'd suggest looking at the test that was added for admin fieldsets. Additional tests can be added to assert the correct aria-describedby attribute for both help_text and errors is present.
​https://github.com/django/django/blob/0b40210e4808937a7c0922e8b7502bff4752faa3/tests/admin_views/tests.py#L7365