[14.0] base_user_role: warning when adding admin to role

When creating a new user role, it is possible to add a user to that role without having added any groups.
If this is saved, all that user’s access rights will be wiped and he will not able to login anymore (Internal Server Error).

base_user_role/models/role.py

@@ -175,3 +175,11 @@ def unlink(self):
         res = super(ResUsersRoleLine, self).unlink()
         users.set_groups_from_roles(force=True)
         return res
+
+    @api.onchange('user_id')
+    def _onchange_user_id(self):
+        if self.user_id and self.user_id._is_admin():
+            return {'warning': {
+                'title': _("Warning"),
+                'message': _("When adding a role to an administrator, make sure no essential groups will be removed."),
+            }}