Hello,

the test case is to simply open a file hosted on a Microsoft SharePoint
server and afterward trying to leave emacs.

The hard part might be to have a SharePoint account...

I opend a file with an 'emacs -Q' instance. The following is the bug report
content:
In GNU Emacs 28.0.50 (build 1, x86_64-w64-mingw32)
 of 2020-07-05 built on CIRROCUMULUS
Repository revision: e3ada2063aa286ea6898a60d95061a77fb752ca8
Repository branch: master
Windowing system distributor 'Microsoft Corp.', version 10.0.18363
System Description: Microsoft Windows 10 Pro (v10.0.1909.18363.1316)

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
File exists, but cannot be read
Parsing archive file...done.
File mode specification error: (file-error Unlocking file Invalid argument
//collaboration.mydummy.com/subjects/foo.docx)

Configured using:
 'configure --without-dbus --host=x86_64-w64-mingw32
 --without-compress-install -C 'CFLAGS=-O2 -static -g3'
 host_alias=x86_64-w64-mingw32 PKG_CONFIG_PATH=/mingw64/lib/pkgconfig'

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: de_DE.UTF-8
  locale-coding-system: cp1252

Major mode: Zip-Archive

Minor modes in effect:
  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
  buffer-read-only: t
  line-number-mode: t
  transient-mark-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message rmc puny rfc822 mml mml-sec
password-cache epa derived epg epg-config gnus-util rmail rmail-loaddefs
text-property-search seq byte-opt gv bytecomp byte-compile cconv
mm-decode mm-bodies mm-encode mail-parse rfc2231 mailabbrev gmm-utils
mailheader sendmail rfc2047 rfc2045 ietf-drums mm-util mail-prsvr
mail-utils arc-mode archive-mode doc-view jka-compr image-mode easymenu
exif dired dired-loaddefs time-date subr-x cl-loaddefs cl-lib 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 term/common-win
tool-bar dnd fontset image regexp-opt fringe tabulated-list replace
newcomment text-mode elisp-mode lisp-mode prog-mode register page
tab-bar menu-bar rfn-eshadow isearch timer select scroll-bar mouse
jit-lock font-lock syntax facemenu font-core term/tty-colors frame
minibuffer 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 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 54351 9648)
 (symbols 48 6728 1)
 (strings 32 18928 1594)
 (string-bytes 1 586074)
 (vectors 16 10443)
 (vector-slots 8 140103 16322)
 (floats 8 38 177)
 (intervals 56 311 0)
 (buffers 992 12))


On Thu, 4 Feb 2021 at 16:21, Eli Zaretskii <eliz@gnu.org> wrote:

> > Date: Thu, 04 Feb 2021 10:00:55 GMT
> > From: lemue301171@freenet.de
> >
> > If an file name is used, which is obviously invalid for some operations,
> > the following can happen:
> > 1. The file gets opened anyway, although an error message states
> > otherwise:
> > - File exists, but cannot be read
> > - File mode specification error: (file-error Unlocking file Invalid
> argument
> > //collaboration.dummyname.com@SSL/DavWWWRoot/subjects/foo bar.docx)
> > 2. Trying to close the buffer triggers simmilar errors
> > 3. Trying to exit emacs leads to a question wheter the file shall be
> saved.
> > - Selecing No now again leads to similar error message, but now emacs
> also freezes (is unresponsive and
> > GUI is no longer updated).
> > - Emacs must be killed via task-manager.
>
> Thanks, but we need a more concrete test case to see what happens in
> these cases and how to fix that.  Could you please provide a full
> detailed recipe to reproduce this starting from "emacs -Q"?
>