bug#29871: 25.3; ZWJ word-boundaries in regexps

[Mark Shoulson]

According to http://unicode.org/reports/tr29/#Word_Boundaries rule WB4,
it would seem that a ZWJ character (U+200D ZERO WIDTH JOINER) between
two "word" characters should not constitute a word boundary.  And yet:

(string-match "\\<" "foo\u200Dfbar" 1)

evaluates to 4 (the 1 is to skip the word-beginning at the start of the
string).  Or you can search for "\\b" or "\\>" and get 3.  Either way,
indicative of a word-break at the ZWJ character.  Is this correct?

~mark


In GNU Emacs 25.3.1 (x86_64-redhat-linux-gnu, GTK+ Version 3.22.19)
 of 2017-09-14 built on buildvm-29.phx2.fedoraproject.org
Configured using:
 'configure --build=x86_64-redhat-linux-gnu
 --host=x86_64-redhat-linux-gnu --program-prefix=
 --disable-dependency-tracking --prefix=/usr --exec-prefix=/usr
 --bindir=/usr/bin --sbindir=/usr/sbin --sysconfdir=/etc
 --datadir=/usr/share --includedir=/usr/include --libdir=/usr/lib64
 --libexecdir=/usr/libexec --localstatedir=/var
 --sharedstatedir=/var/lib --mandir=/usr/share/man
 --infodir=/usr/share/info --with-dbus --with-gif --with-jpeg --with-png
 --with-rsvg --with-tiff --with-xft --with-xpm --with-x-toolkit=gtk3
 --with-gpm=no --with-xwidgets --with-modules
 build_alias=x86_64-redhat-linux-gnu host_alias=x86_64-redhat-linux-gnu
 'CFLAGS=-DMAIL_USE_LOCKF -O2 -g -pipe -Wall -Werror=format-security
 -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong
 --param=ssp-buffer-size=4 -grecord-gcc-switches
 -specs=/usr/lib/rpm/redhat/redhat-hardened-cc1 -m64 -mtune=generic'
 LDFLAGS=-Wl,-z,relro
 PKG_CONFIG_PATH=:/usr/lib64/pkgconfig:/usr/share/pkgconfig'

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

Important settings:
  value of $LANG: en_US.utf8
  value of $XMODIFIERS: @im=none
  locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

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
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent messages:
../../usr/share/emacs/site-lisp/uim-el/uim-key.el: (lambda (x) ...) quoted with 
' rather than with #' [3 times]
../../usr/share/emacs/site-lisp/uim-el/uim-preedit.el: (lambda (x) ...) quoted 
with ' rather than with #'
../../usr/share/emacs/site-lisp/uim-el/uim-candidate.el: (lambda (x) ...) 
quoted with ' rather than with #' [5 times]
../../usr/share/emacs/site-lisp/uim-el/uim-helper.el: (lambda (x) ...) quoted 
with ' rather than with #' [2 times]
../../usr/share/emacs/site-lisp/uim-el/uim.el: (lambda (x) ...) quoted with ' 
rather than with #' [9 times]
../../usr/share/emacs/site-lisp/uim-el/uim-leim.el: (lambda (x) ...) quoted 
with ' rather than with #'
uim.el: starting uim-el-helper-agent... done
uim.el: starting uim-el-agent... done
Loading /usr/share/emacs/site-lisp/site-start.d/uim-init.el (source)...done
For information about GNU Emacs and the GNU system, type C-_ C-a.

Load-path shadows:
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Features:
(shadow sort mail-extr emacsbug message idna dired format-spec rfc822
mml mml-sec password-cache epg gnus-util mm-decode mm-bodies mm-encode
mail-parse rfc2231 mailabbrev gmm-utils mailheader sendmail rfc2047
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package epg-config seq byte-opt gv bytecomp byte-compile cl-extra
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uim-helper uim-candidate uim-preedit uim-key uim-util uim-debug
uim-keymap uim-var uim-version mule-util tooltip eldoc electric uniquify
ediff-hook vc-hooks lisp-float-type mwheel x-win term/common-win x-dnd
tool-bar dnd fontset image regexp-opt fringe tabulated-list newcomment
elisp-mode lisp-mode prog-mode register page menu-bar rfn-eshadow timer
select scroll-bar mouse jit-lock font-lock syntax facemenu font-core
frame cl-generic cham georgian utf-8-lang misc-lang vietnamese tibetan
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custom widget hashtable-print-readable backquote dbusbind inotify
dynamic-setting system-font-setting font-render-setting xwidget-internal
move-toolbar gtk x-toolkit x multi-tty make-network-process emacs)

Memory information:
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