bug#43835: 28.0.50; auto-hscroll-mode/current-line + show-paren-mode + gnus-summary-mode = bug

[Stephen Berman]

On Tue, 06 Oct 2020 22:05:42 +0200 Stephen Berman <stephen.berman@gmx.net> 
wrote:

> On Tue, 06 Oct 2020 22:10:26 +0300 Eli Zaretskii <eliz@gnu.org> wrote:
>
>>> I can reproduce this problem in Emacs 26, 27 and master, but I have only
>>> been able to reproduce it in Gnus summary buffers, and only on the last
>>> line of the summary and only when this line is longer than window-width
>>> (so that hscrolling can happen) and the line ends with a pair of paren
>>> characters (brackets and braces also show the effect) and
>>> show-paren-mode is enabled.  Sometimes I have seen the hscroll get
>>> restored after a several seconds, but other times this does not happen
>>> (though I haven't tried waiting for more than maybe 15-20 seconds).
>>
>> Does the hscroll get restored if you type "M-x"?
>
> As soon as I type `M-x' I see the line scroll left and the cursor at the
> end, and it remains like that, but if I then type `C-g', the line
> scrolls back to the right and point is again not visible, as in step 8.

I haven't yet rebuilt with --enable-checking='yes,glyphs', but I just
made a new, perhaps relevant, observation: after step 8 of the recipe,
i.e. with point at the end of the line but hscrolling undone, if I move
the mouse pointer to a position that pops up a tooltip (i.e., over a
tool-bar icon or a mode-line element), then with
x-gtk-use-system-tooltips set to t nothing changes but with
x-gtk-use-system-tooltips set to nil, the hscroll is restored, like with
`M-x' before `C-g', and the hscroll stays when I move the mouse so that
the tooltip vanishes, but if I then type `C-g', the hscroll is undone
again (and point remains at the end of the line, out of view).

Steve Berman