bug#43723: 27.1; Errors in file-extended-attributes prevent from saving buffer

[Eli Zaretskii]

When some volume is mounted such that file-extended-attributes fails
for files there (because the agent used to mount doesn't support ACLs
or SELinux), this prevents users from saving their edits to files on
that volume, because file-extended-attributes signals an error.  This
appears as a regression to users because Emacs 26 silently ignored
such errors.

To allow users to save the files in these cases, but still keep them
informed about the loss of potentially important attributes, Emacs
should probably warn about this, allow the user to decide he/she wants
to ignore the problem, and record this fact somewhere, to avoid asking
the same question again for the same volume.

Bonus points for providing a defcustom where users could state in
advance the volumes for which such errors should be ignored.


In GNU Emacs 27.1 (build 1, i686-pc-mingw32)
 of 2020-08-11 built on HOME-C4E4A596F7
Windowing system distributor 'Microsoft Corp.', version 5.1.2600
System Description: Microsoft Windows XP Service Pack 3 (v5.1.0.2600)

Recent messages:
Saving file d:/gnu/git/emacs/trunk/.git/COMMIT_EDITMSG...
Wrote d:/gnu/git/emacs/trunk/.git/COMMIT_EDITMSG
Mark set [7 times]
Sending...
Added to d:/usr/eli/rmail/SENT.MAIL
Sending email done
Sending...done
Showing message 2726...done
Showing message 2726...done
Modification-flag cleared

Configured using:
 'configure -C --prefix=/d/usr --with-wide-int --with-modules
 'CFLAGS=-O2 -gdwarf-4 -g3''

Configured features:
XPM JPEG TIFF GIF PNG RSVG SOUND NOTIFY W32NOTIFY ACL GNUTLS LIBXML2
HARFBUZZ ZLIB TOOLKIT_SCROLL_BARS MODULES THREADS JSON PDUMPER LCMS2
GMP

Important settings:
  value of $LANG: ENU
  locale-coding-system: cp1255

Major mode: RMAIL

Minor modes in effect:
  shell-dirtrack-mode: t
  desktop-save-mode: t
  save-place-mode: t
  show-paren-mode: t
  display-battery-mode: t
  display-time-mode: t
  tooltip-mode: t
  global-eldoc-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
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  temp-buffer-resize-mode: t
  buffer-read-only: t
  line-number-mode: t

Load-path shadows:
d:/usr/share/emacs/site-lisp/soap-inspect hides 
d:/usr/share/emacs/27.1/lisp/net/soap-inspect
d:/usr/share/emacs/site-lisp/soap-client hides 
d:/usr/share/emacs/27.1/lisp/net/soap-client

Features:
(shadow emacsbug apropos tabify grep compile ibuf-ext ibuffer
ibuffer-loaddefs arc-mode archive-mode debug backtrace hi-lock double
mouse-copy mouse-drag m4-mode xscheme scheme tramp tramp-loaddefs
trampver tramp-integration files-x tramp-compat parse-time iso8601
pulse etags fileloop generator skeleton face-remap image-mode exif
completion cua-gmrk cua-rect rect cua-base pp descr-text ffap
ebuff-menu iso-transl smerge-mode diff quail cl-print misearch
multi-isearch eieio-opt speedbar sb-image ezimage dframe find-func
thingatpt help-fns radix-tree dabbrev rmailout shr-color color shr
url-cookie url-domsuf url-util url-parse url-vars svg xml dom
browse-url shell pcomplete comint ansi-color rfc2104 gnutls
network-stream nsm mail-extr smtpmail auth-source json map mailalias
sendmail cl-extra help-mode cc-awk view enriched conf-mode texinfo
make-mode jka-compr vc-cvs bat-mode vc-dispatcher vc-bzr noutline
outline flyspell add-log vc-git diff-mode easy-mmode bug-reference
mule-util info qp rmailsum rmailmm message rmc puny format-spec rfc822
mml mml-sec password-cache epa epg epg-config gnus-util
text-property-search time-date subr-x seq mm-decode mm-bodies
mm-encode mailabbrev gmm-utils mailheader mail-parse rfc2231 rmail
rmail-loaddefs rfc2047 rfc2045 ietf-drums mm-util mail-prsvr
mail-utils desktop frameset server find-lisp dired dired-loaddefs
filecache mairix cus-edit cus-start cus-load wid-edit saveplace
midnight ispell derived generic-x cc-mode cc-fonts easymenu cc-guess
cc-menus cc-cmds cc-styles cc-align cc-engine cc-vars cc-defs paren
xref cl-seq project ring eieio byte-opt bytecomp byte-compile cconv
eieio-core cl-macs gv eieio-loaddefs cl-loaddefs cl-lib battery time
tooltip eldoc electric uniquify ediff-hook vc-hooks lisp-float-type
mwheel dos-w32 ls-lisp disp-table term/w32-win w32-win w32-vars
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prog-mode register page tab-bar menu-bar rfn-eshadow isearch timer
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term/tty-colors frame minibuffer cl-generic cham georgian utf-8-lang
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eucjp-ms cp51932 hebrew greek romanian slovak czech european ethiopic
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epa-hook jka-cmpr-hook help simple abbrev obarray 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 w32notify w32 lcms2
multi-tty make-network-process emacs)

Memory information:
((conses 16 4156244 469197)
 (symbols 48 40145 57)
 (strings 16 316024 26318)
 (string-bytes 1 7689602)
 (vectors 16 73714)
 (vector-slots 8 2294162 512108)
 (floats 8 324 643)
 (intervals 40 922715 7602)
 (buffers 888 319))