res_user_group_ids_privilege

The access rights grid is assembled by res_user_group_ids, which generates a form view at runtime. Each privilege in that generated form is rendered by this widget.

A row is a selection or a boolean, plus a small icon that opens a popover explaining what the selected group grants. The widget works out which group is currently selected, which group is implied by another selection, and whether any of them conflict.

It is registered in the fields registry like any other widget, which is why it turns up in a registry listing. That is the only sense in which it is a widget you could use.

The part of this that matters outside a development team is the warning triangle. When two selected groups are marked as disjoint, meaning they should not be held together, this row stops showing an information icon and shows a red triangle instead.

Administrators tend to read that as decoration. It is not. It is Odoo saying the combination of access rights on this user is contradictory, and it is worth stopping to read the popover before saving.

There is no correct example of applying this widget yourself. The source says so directly:

/*
 * /!\ This widget is not meant to be used anywhere else than inside form view
 * dynamically generated by the res_user_group_ids widget.
 */

What you apply is the parent, which builds the rows itself:

<field name="group_ids" widget="res_user_group_ids" nolabel="1"/>

The dependency is not a convention, it is structural. In setup the component reaches into its environment:

setup() {
    this.isDebug = odoo.debug;
    this.popover = usePopover(ResUserGroupIdsPopover);
    this.groups = this.env.resUserGroupsInfo.groups;
}

resUserGroupsInfo is put into a child sub-environment by res_user_group_ids. Nothing else in Odoo provides it. Put this widget on an ordinary field and the lookup fails immediately, because the environment has no such key. That is why it is registered but has zero usages: the registration exists so the generated form can resolve it by name.

The icon logic is the useful part to know:

get infoButtonClassnames() {
    const invisible = !this.isSet && !this.impliedGroup?.id;
    const isDisjoint = this.isDisjoint;
    return {
        ...
        "fa-info-circle": !isDisjoint,
        "fa-exclamation-triangle": isDisjoint,
        "link-danger": isDisjoint,
    };
}

Three states. No icon at all when nothing is set and nothing is implied. An information circle when a group is selected or implied and everything is consistent. A red exclamation triangle when the selected group is disjoint from another the user holds.

The row also distinguishes a group the administrator chose from one that arrived through implication. A privilege the user did not set explicitly but holds anyway, because another group implies it, still shows an icon and names the implying group in the popover. That is the mechanism behind the common support question of why a user has an access right nobody granted them.

No change. Diffing the registration between the 19.0 and 20.0 branches shows no options added or removed and no registration changes.

One Odoo 19 registration variant, form.hr_presence_status_private, was removed from a neighboring widget in Odoo 20, but this one keeps both of its registrations.