bug#59721: 30.0.50; tab bar groups are not ordered properly

[Mickey Petersen <mickey@masteringemacs.org>]

Juri Linkov <juri@linkov.net> writes:

>> 1. Enable tab-bar-mode and then alter tab-bar-format to show
>> groups. Something like this:
>>
>>   (setq tab-bar-format '(tab-bar-format-history
>> tab-bar-format-tabs-groups tab-bar-separator
>> tab-bar-format-add-tab))
>>
>> 2. Create three tabs: A, B, C.  Now switch to A and use M-x
>> tab-bar-change-tab-group and name it "foo".  Now switch to C and name
>> it "foo" also.
>>
>> 3. The tab bar groups are _not_ merged; with a large array of tab
>> bars, this causes endless confusion as there are man duplicae tab
>> groups.  You would expect a tab group to coalesce like tab group
>> members into a singular tab group --- that is after all their purpose.
>
> Thanks for the bug report.  We had a discussion about this problem
> in the past, and in the result we arrived at such a solution that the
> customizable variable `tab-bar-tab-post-change-group-functions' provides
> an option `tab-bar-move-tab-to-group', so that when you select it,
> then after changing the group name the tab is moved to its tab group.

I did not check if that solves it, but this issue -- and how I discovered it -- manifests itself when you use `display-buffer-in-[new]-tab' and set a tab group that way.

This can result in a large amount of distinct tab group entries for the same tab group; does `tab-bar-tab-post-change-group-functions' also resolve this?

Because just about anybody who'd use said display buffer action would find themselves in this predicament and that variable (and subsequently adding that function to it) is... unintuitive.