ChoiceWidget.optgroups() doesn't group choices without a group together

[Riccardo Di Virgilio]

I'm having problems writing template for custom controls (a bootstrap button bar) using optgroup.
the problem is that optgroup is not grouping choices without groups, this makes very hard to create several button bars that grouped togheter:

from django.forms.widgets import ChoiceWidget

w = ChoiceWidget(choices = [
    ("one", 1),
    ("two", 2), [
        "italian", (
            ("uno", 1),
            ("due", 2)
        )
    ]
])

now see how choices are grouped from optgroup:

import json

print(json.dumps(w.optgroups("name", "one"), indent = 4))

[
    [
        null,
        [
            {
                "name": "name",
                "value": "one",
                "label": 1,
                "selected": true,
                "index": "0",
                "attrs": {
                    "checked": true
                },
                "type": null,
                "template_name": null
            }
        ],
        0
    ],
    [
        null,
        [
            {
                "name": "name",
                "value": "two",
                "label": 2,
                "selected": false,
                "index": "1",
                "attrs": {},
                "type": null,
                "template_name": null
            }
        ],
        1
    ],
    [
        "italian",
        [
            {
                "name": "name",
                "value": "uno",
                "label": 1,
                "selected": false,
                "index": "2_0",
                "attrs": {},
                "type": null,
                "template_name": null
            },
            {
                "name": "name",
                "value": "due",
                "label": 2,
                "selected": false,
                "index": "2_1",
                "attrs": {},
                "type": null,
                "template_name": null
            }
        ],
        2
    ]
]

this means that if choices are flats (no groups) you are getting a number of groups that is the same of the number of choices, and in order to fix this you need to use the grouping filters on the template in order to regroup choices.

I think this is a bug, and flat choices should be grouped together as None by optgroup method

thanks

[Tim Graham]

It might be fine -- can you offer a patch?

[Riccardo Di Virgilio]

Sure i'll do this in the next days.
Is it ok to provide just the function?

thanks!

[Carlton Gibson]

The suggested fix in ​PR#9621 breaks choice ordering: it will group all ungrouped choices at whatever index the first ungrouped happens to have. This isn't something we should impose. (We may want to present ungrouped default/common choices at the beginning, some groups, and then some ungrouped "other" choices at the end, for one example.)

How we might preserve current behaviour whilst allowing grouping of ungrouped items seems tricky at best. It looks to me as if a better approach would be to recommend using a custom widget and overriding optgroups in order to gather ungrouped choices if that is what's required.

I put this example on the PR. It's just an untested sketch but it should demonstrate the idea:

def optgroups(self, name, value, attrs=None):
    """Override optgroups to group ungrouped choices at end."""
    ret = []
    none_choices = []
    max_index = 0
    for group_name, choices, index in super().optgroups(name, value, attrs):
        if group_name is None:
            none_choices.append(choices)
        else:
            max_index = max(max_index, index) 
            ret.append((group_name, choices, index))
    
    ret.append((None, none_choices, max_index +1))
    return ret

As such I'd probably be inclined to close this as Won't Fix.

(We could document the suggestion, but "override methods to customise behaviour" is just OOP.)