Pull Request for Issue #28522 (comment).

Summary of Changes

When deleting one or more usergroups, the lftand rgt values in the #__usergroups table are not recalculated, i.e. the nested set tree is not rebuilt.

This PR adds the missing function call for that purpose to the delete routine of the Usergroup table class.

Testing Instructions

1. On a clean, new installation, check with an SQL client (e.g. phpMyAdmin when using MySQL or MariaDB) the content of the #__usergroups as follows:
   

2. In backend as a super user and not being member of one of these groups, delete the usergroup "Manager", which will also delete its child group "Administrator". (You can also delete others but then it's on you to calculate the right lftand rgt values to check if this PR is right.)

3. Check again with an SQL client the content of the #__usergroups with the same SQL query as before.

Result: lftand rgt values in the #__usergroups table haven't changed for the remaining records:

4. If you want to delete in the next test the same user group as in the test before: Make a new installation.

5. Apply the patch.

6. Repeat steps 2 and 3.

Result: lftand rgt values in the #__usergroups table have been recalculated. If you have deleted the group as described above, it should look as follows:

The calculation scheme is as follows for that example:

Expected result

The lftand rgt values in the #__usergroups table are correctly recalculated.

Actual result

The lftand rgt values in the #__usergroups table are not recalculated.

Documentation Changes Required

None.

Additional information

When inserting new user groups or moving some around between parent groups, the lftand rgt values in the #__usergroups table are recalculated without this patch using the same function, so I assume the lftand rgt values are still relevant.