bug#42622: 26.3; Scheme mode: Wrong indentation (no indentation) when pressing tab

[Kjetil Matheussen <k.s.matheussen@gmail.com>]

Follow-up: It appears as if the bug is not present in 26.2, at least
when using this recipe.

On Thu, Jul 30, 2020 at 11:08 AM Kjetil Matheussen
<k.s.matheussen@gmail.com> wrote:
>
> Recipe to reproduce:
> (note that it's important that you do _exactly_ as described. The bug
> happens very often (and is extremely annoying), but it's very unclear
> what triggers it.)
>
> 1. wget http://users.notam02.no/~kjetism/emacsindentationbug.scm
> 2. emacs emacsindentationbug.scm
> 3. Press Ctrl + S, search for "define column-widths"
> 4. The cursor should now be placed at line 2790
> 5. Press down-arrow so that that cursor is placed at line 2791
> 6. Press up -arrow so that the cursor is placed at line 2790 again.
> 7. Press TAB.
> 8. The line is wrongly indented (no indentation).
>
>
> In GNU Emacs 26.3 (build 1, x86_64-pc-linux-gnu, X toolkit, Xaw scroll bars)
>  of 2020-07-18 built on localhost.localdomain
> Windowing system distributor 'Fedora Project', version 11.0.11405000
> System Description: Fedora release 20 (Heisenbug)
>
> Recent messages:
> Checking 24 files in /home/kjetil/site/share/emacs/26.3/lisp/cedet...
> Checking 57 files in /home/kjetil/site/share/emacs/26.3/lisp/calendar...
> Checking 87 files in /home/kjetil/site/share/emacs/26.3/lisp/calc...
> Checking 105 files in /home/kjetil/site/share/emacs/26.3/lisp/obsolete...
> Checking for load-path shadows...done
> previous-line: Beginning of buffer [3 times]
> Auto-saving...done
> previous-line: Beginning of buffer [5 times]
> Buffer *unsent mail to bug-gnu-emacs@gnu.org* modified; kill anyway? (y or n) y
> Mark saved where search started [2 times]
>
> Configured using:
>  'configure --prefix=/home/kjetil/site --with-x-toolkit=lucid'
>
> Configured features:
> XPM JPEG TIFF GIF PNG SOUND DBUS GSETTINGS GLIB NOTIFY LIBSELINUX GNUTLS
> LIBXML2 FREETYPE XFT ZLIB TOOLKIT_SCROLL_BARS LUCID X11 XDBE XIM THREADS
>
> Important settings:
>   value of $LANG: en_US.UTF-8
>   locale-coding-system: utf-8-unix
>
> Major mode: Scheme
>
> Minor modes in effect:
>   diff-auto-refine-mode: t
>   iswitchb-mode: t
>   shell-dirtrack-mode: t
>   tooltip-mode: t
>   global-eldoc-mode: t
>   electric-indent-mode: t
>   mouse-wheel-mode: t
>   menu-bar-mode: t
>   file-name-shadow-mode: t
>   global-font-lock-mode: t
>   font-lock-mode: t
>   auto-composition-mode: t
>   auto-encryption-mode: t
>   auto-compression-mode: t
>   column-number-mode: t
>   line-number-mode: t
>   transient-mark-mode: t
>
> Load-path shadows:
> None found.
>
> Features:
> (pp shadow sort mail-extr emacsbug message rmc puny rfc822 mml mml-sec
> epa derived epg gnus-util rmail rmail-loaddefs mm-decode mm-bodies
> mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader help-fns
> radix-tree align two-column iso-transl help-mode xref project ffap
> thingatpt make-mode dired-aux dired dired-loaddefs cmuscheme conf-mode
> cc-mode cc-fonts cc-guess cc-menus cc-cmds misearch multi-isearch vc-git
> diff-mode easy-mmode scheme elec-pair color-theme wid-edit cl sendmail
> rfc2047 rfc2045 ietf-drums mm-util mail-prsvr mail-utils reporter
> iswitchb finder-inf scala-mode2-autoloads package epg-config
> url-handlers url-parse url-vars python easymenu tramp-sh tramp
> tramp-compat tramp-loaddefs trampver ucs-normalize shell pcomplete
> parse-time format-spec advice auth-source cl-seq eieio eieio-core
> cl-macs eieio-loaddefs password-cache json map seq byte-opt gv bytecomp
> byte-compile cconv comint ring ansi-color edmacro kmacro cc-styles
> cc-align cc-engine cc-vars cc-defs cl-loaddefs cl-lib time-date
> mule-util tooltip eldoc electric uniquify ediff-hook vc-hooks
> lisp-float-type mwheel term/x-win x-win term/common-win x-dnd tool-bar
> dnd fontset image regexp-opt fringe tabulated-list replace newcomment
> text-mode elisp-mode lisp-mode prog-mode register page menu-bar
> rfn-eshadow isearch timer select scroll-bar mouse jit-lock font-lock
> syntax facemenu font-core term/tty-colors frame cl-generic cham georgian
> utf-8-lang misc-lang vietnamese tibetan thai tai-viet lao korean
> japanese eucjp-ms cp51932 hebrew greek romanian slovak czech european
> ethiopic indian cyrillic chinese composite charscript charprop
> case-table epa-hook jka-cmpr-hook help simple abbrev obarray minibuffer
> cl-preloaded nadvice loaddefs button faces cus-face macroexp files
> text-properties overlay sha1 md5 base64 format env code-pages mule
> custom widget hashtable-print-readable backquote threads dbusbind
> inotify dynamic-setting system-font-setting font-render-setting
> x-toolkit x multi-tty make-network-process emacs)
>
> Memory information:
> ((conses 16 1270767 168270)
>  (symbols 48 37217 2)
>  (miscs 40 934 9001)
>  (strings 32 113664 7701)
>  (string-bytes 1 3016589)
>  (vectors 16 60156)
>  (vector-slots 8 1962000 165392)
>  (floats 8 227 660)
>  (intervals 56 160970 1318)
>  (buffers 992 116)
>  (heap 1024 108471 4922))