Cyril Brulebois <k...@debian.org> (2021-05-21):
> There might be simpler (shorter) ways to trigger this but the following
> is robust:
> 
>  - Initially detected while testing an encrypted LVM install in Swedish
>    (confirming all hangs go away), when reaching the partition layout
>    confirmation dialog, the selected entry is the last one in the list,
>    but the selection isn't seen. One might wonder where the focus is,
>    why no entry was selected, etc. Since that can happen in various
>    places, I think users might get confused. That should not be specific
>    to Swedish, it just happens to be the first occurrence I noticed.

That particular part seems solved with my current hackish patch series.

>  - Slightly shorter (`kvm -m 1G -cdrom mini.iso`, no disk layout or even
>    disk required), pick a language like French and all default choices,
>    until the mirror country selection, pick the very last one
>    (États-Unis), and on the mirror host selection, pick the very last
>    one again (the actual hostname doesn't matter). Now, on the next
>    dialog, hit “Revenir en arrière” (Back), and see the selected
>    hostname isn't focussed. Another step back shows the selected country
>    isn't focussed either. That should happen with other languages as
>    well, using French has the main advantage for me to get the
>    appropriate keyboard layout automatically plus get two “back” steps
>    that exhibit the problem (other countries might not have a mirror
>    list as big as the US one).

That one is strange:
 - getting back to mirror hostname selection is still buggy;
 - getting back to mirror country selection is no longer buggy.

I'm not sure whether my current approach can be refined to work in all
cases, but solving at least the obvious “forward-only” (= no step back)
issue that was seen at least on the layout confirmation screen… seems
worth considering for bullseye, even if it's ugly and doesn't solve all
cases? And maybe users are going to tell us about other occurrences
because of different languages/options combinations that result in
different layout, triggering the scrolling issue or not.

> Next on my list of things to try was adding a pointer to the frontend
> object (and its `data` member) so that we could keep the callback alive
> until set_text_in_idle has done its job. I thought it might need some
> mutex or locking around a counter of pending set_text calls and I
> haven't touched that yet. And today, the following rang a bell… :)
>   https://salsa.debian.org/installer-team/cdebconf/-/merge_requests/7

Merging that on top of my code didn't seem to make any difference
regarding the “back to the mirror hostname selection” issue that
remains.

I'll try and tidy up my patches, and push a branch somewhere, also
posting traces that show that events seem to have happened in the right
order.


Cheers,
-- 
Cyril Brulebois (k...@debian.org)            <https://debamax.com/>
D-I release manager -- Release team member -- Freelance Consultant

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