starting from 'emacs -Q':
Toggle-truncate-lines (so that long lines are truncated)
Evaluate the following:
(setq auto-hscroll-mode 'current-line)
(setq hscroll-margin 5)
(setq hscroll-step 1)
Insert enough text such that the line starts to hscroll
On the line directly below, insert enough text to fill about half the
width of the frame
Move point to the long line near the end (must be hscrolling the single
line)
Move point down to the next line, it should hscroll even though it does
not need to
See the animated gifs on this post:
https://www.reddit.com/r/emacs/comments/wgef0b/looking_for_better_alternative_to_autohscrollmode/

I have attached a patch that I think fixes the issue.  Please tell me
how to proceed, and what other information you need.


In GNU Emacs 27.2 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.20)
 of 2021-11-22 built on erik-lair
Windowing system distributor 'The X.Org Foundation', version 11.0.12013000
System Description: Ubuntu 20.04.3 LTS

Recent messages:
Type C-c C-c to finish, C-c C-k to cancel, and M-p and M-n to recover older
messages
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Commands: m, u, t, RET, g, k, S, D, Q; q to quit; h for help
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Saving file /home/erik/projects/emacs_build/emacs_git/.git/COMMIT_EDITMSG...
Wrote /home/erik/projects/emacs_build/emacs_git/.git/COMMIT_EDITMSG
Git finished

Configured features:
XPM JPEG TIFF GIF PNG SOUND GPM DBUS GSETTINGS GLIB NOTIFY INOTIFY
LIBSELINUX GNUTLS FREETYPE HARFBUZZ XFT ZLIB TOOLKIT_SCROLL_BARS GTK3
X11 XDBE XIM MODULES THREADS PDUMPER GMP

Important settings:
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Major mode: C/*l

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Load-path shadows:
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Memory information:
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