bug#64164: 29.0.92; buffer-file-coding-system changes unexpectedly after saving

[miranda]

i am trying to edit remote files on another macOS system, using Tramp's 
ssh: method. i am running `emacs -Q`.

when i open any file on this remote system, the initial value of 
`buffer-file-coding-system` is what i would expect, i.e. undecided-unix 
or utf-8-unix, depending on whether the file contains non-ASCII 
characters.

however, after saving the file, `buffer-file-coding-system` suddenly 
changes to utf-8-hfs-mac. any subsequent save then changes all the line 
endings to CR, which i have not actively used since 2001 or so... :-)

i can use `set-buffer-file-coding-system` to set utf-8-unix, but the 
problem then occurs again after the next save. other remotes (Linux 
systems) do not exhibit the issue.

Emacs 28.2 works as expected.

i am using the build from https://emacsformacosx.com/builds

best,
miranda


In GNU Emacs 29.0.92 (build 1, x86_64-apple-darwin15.6.0, NS
 appkit-1404.47 Version 10.11.6 (Build 15G22010)) of 2023-06-18 built on
 builder10-11.lan
Windowing system distributor 'Apple', version 10.3.1561
System Description:  Mac OS X 10.13.6

Configured using:
 'configure --with-ns '--enable-locallisppath=/Library/Application
 Support/Emacs/${version}/site-lisp:/Library/Application
 Support/Emacs/site-lisp' --with-modules
 CFLAGS=-DNSTextAlignmentRight=NSRightTextAlignment --with-x-toolkit=no'

Configured features:
ACL GMP GNUTLS JSON LIBXML2 MODULES NOTIFY KQUEUE NS PDUMPER SQLITE3
THREADS TOOLKIT_SCROLL_BARS ZLIB

Important settings:
  value of $LANG: fi_FI.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  eldoc-mode: t
  show-paren-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  line-number-mode: t
  indent-tabs-mode: t
  transient-mark-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message mailcap yank-media puny dired
dired-loaddefs rfc822 mml mml-sec password-cache epa derived epg rfc6068
epg-config gnus-util text-property-search time-date subr-x mm-decode
mm-bodies mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader
cl-loaddefs cl-lib sendmail rfc2047 rfc2045 ietf-drums mm-util
mail-prsvr mail-utils rmc iso-transl tooltip cconv eldoc paren electric
uniquify ediff-hook vc-hooks lisp-float-type elisp-mode mwheel
term/ns-win ns-win ucs-normalize mule-util term/common-win tool-bar dnd
fontset image regexp-opt fringe tabulated-list replace newcomment
text-mode lisp-mode prog-mode register page tab-bar menu-bar rfn-eshadow
isearch easymenu timer select scroll-bar mouse jit-lock font-lock syntax
font-core term/tty-colors frame minibuffer nadvice seq simple cl-generic
indonesian philippine 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 emoji-zwj charscript charprop case-table epa-hook
jka-cmpr-hook help abbrev obarray oclosure cl-preloaded button loaddefs
theme-loaddefs faces cus-face macroexp files window text-properties
overlay sha1 md5 base64 format env code-pages mule custom widget keymap
hashtable-print-readable backquote threads kqueue cocoa ns multi-tty
make-network-process emacs)

Memory information:
((conses 16 37468 8247)
 (symbols 48 5045 0)
 (strings 32 12567 2096)
 (string-bytes 1 355935)
 (vectors 16 10369)
 (vector-slots 8 155077 9845)
 (floats 8 21 23)
 (intervals 56 217 0)
 (buffers 976 10))