bug#32246: 27.0.50; files-tests failure on Cygwin

[Ken Brown]

I'm getting a failure of
files-tests-file-name-non-special-file-name-case-insensitive-p on
Cygwin:

Test files-tests-file-name-non-special-file-name-case-insensitive-p 
backtrace:
  signal(ert-test-failed (((should (equal (file-name-case-insensitive-
  ert-fail(((should (equal (file-name-case-insensitive-p nospecial) (f
  (if (unwind-protect (setq value-532 (apply fn-530 args-531)) (setq f
  (let (form-description-534) (if (unwind-protect (setq value-532 (app
  (let ((value-532 'ert-form-evaluation-aborted-533)) (let (form-descr
  (let* ((fn-530 #'equal) (args-531 (condition-case err (let ((signal-
  (progn (let* ((fn-530 #'equal) (args-531 (condition-case err (let ((
  (unwind-protect (progn (let* ((fn-530 #'equal) (args-531 (condition-
  (let* ((temporary-file-directory (file-truename temporary-file-direc
  (closure (t) nil (let* ((temporary-file-directory (file-truename tem
  ert--run-test-internal(#s(ert--test-execution-info :test #s(ert-test
  ert-run-test(#s(ert-test :name files-tests-file-name-non-special-fil
  ert-run-or-rerun-test(#s(ert--stats :selector (not (tag :unstable))
  ert-run-tests((not (tag :unstable)) #f(compiled-function (event-type
  ert-run-tests-batch((not (tag :unstable)))
  ert-run-tests-batch-and-exit((not (tag :unstable)))
  eval((ert-run-tests-batch-and-exit '(not (tag :unstable))))
  command-line-1(("-L" ":../../master/test" "-l" "ert" "-l" "lisp/file
  command-line()
  normal-top-level()
Test files-tests-file-name-non-special-file-name-case-insensitive-p 
condition:
    (ert-test-failed
     ((should
       (equal
        (file-name-case-insensitive-p nospecial)
        (file-name-case-insensitive-p tmpfile)))
      :form
      (equal t nil)
      :value nil :explanation
      (different-atoms t nil)))
   FAILED  40/78 
files-tests-file-name-non-special-file-name-case-insensitive-p (0.003135 
sec)

A bisection shows that the problem started with the following commit:

commit e75c57f10ee9418599398361b0676f48d265fb12
Author: Michael Albinus <michael.albinus@gmx.de>
Date:   Sun Jun 3 14:30:41 2018 +0200

    Extend file-name-non-special

Please let me know what I can do to help track this down.

Ken


In GNU Emacs 27.0.50 (build 21, x86_64-unknown-cygwin, GTK+ Version 3.22.28)
 of 2018-07-22 built on moufang
Repository revision: f3f67cf0b9a6388d423e048a7aafad2eb531b5a5
Windowing system distributor 'The Cygwin/X Project', version 11.0.12000000
Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.

Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND DBUS GSETTINGS NOTIFY ACL
GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB TOOLKIT_SCROLL_BARS
GTK3 X11 THREADS LCMS2

Important settings:
  value of $LANG: en_US.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
  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
  line-number-mode: t
  transient-mark-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message rmc puny seq byte-opt gv
bytecomp byte-compile cconv dired dired-loaddefs format-spec rfc822 mml
easymenu mml-sec password-cache epa derived epg epg-config gnus-util
rmail rmail-loaddefs 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 elec-pair 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
gfilenotify lcms2 dynamic-setting system-font-setting
font-render-setting move-toolbar gtk x-toolkit x multi-tty
make-network-process emacs)

Memory information:
((conses 16 94354 9921)
 (symbols 48 20128 1)
 (miscs 40 39 93)
 (strings 32 28382 1874)
 (string-bytes 1 749578)
 (vectors 16 14231)
 (vector-slots 8 503648 13212)
 (floats 8 48 86)
 (intervals 56 207 0)
 (buffers 992 12))