bug#46557: 28.0.50; Visual glitches in text mode when tab-bar visibility is altered at load time

[martin rudalics]

>> The following recipe creates a broken visual appearance of emacs in text
>> mode, at least on GNU/Linux:
>>
>> 1) Create a test.el file with these lines:
>>
>> (set-frame-parameter nil 'tab-bar-lines 0)
>> (set-frame-parameter nil 'tab-bar-lines 1)
>> (set-frame-parameter nil 'tab-bar-lines 0)
>
> This bug report can't be closed, because it seems
> this problem is related to https://debbugs.gnu.org/46827#153
> where setting tab-bar-lines to 1 changes tab-bar-lines to 2.
> Reproducible test case:
>
> (progn
>    (set-frame-parameter nil 'tab-bar-lines 1)
>    (let ((lines (frame-parameter nil 'tab-bar-lines)))
>      (sit-for 0)
>      (list lines (frame-parameter nil 'tab-bar-lines))))
>
> returns (1 2)

But IIUC the latter holds for a GUI only.  You cannot get two lines on a
TTY unless you wrap the tab bar (if that is possible on a TTY).

martin