bug#36423: 27.0.50; electric-pair-mode not working properly depending of file content.

[Ergus <spacibba@aol.com>]

In electric-pair-mode there are some files where inserting one " does
not insert the pair ". But on the other hand when I try to insert a
second " it inserts a pair for it so it ends with """.

It does not happen when the file is empty but for me it happens with
this file content.

---------------------------------------
#ifndef _SparseMatrix_functions_hpp_
#define _SparseMatrix_functions_hpp_



#endif
--------------------------------------- 

The behavior changes sometimes inserting a new line instead of the first
", or just not inserting any pair at all. This looks like an issue in a
backward search for a pair or something. Because it changes if withing
the define region or not.

When a region is active there is not issue and the quotes are inserted
in pairs around the region as expected.

This was reproduced with:

emacs -Q file.hpp
M-x electric-pair-modes

In GNU Emacs 27.0.50 (build 4, x86_64-pc-linux-gnu, GTK+ Version 3.24.9)
 of 2019-06-28 built on Ergus
Repository revision: cb182ce6f8d2fa6e1509252fecc2b0e504e36d63
Repository branch: master
System Description: Arch Linux



Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
main.hpp has auto save data; consider M-x recover-this-file
Electric-Pair mode enabled
funcall-interactively: End of buffer [3 times]
C-x <up> is undefined
user-error: End of history; no default available

Configured using:
 'configure --prefix=/home/ergo/PhD/emacs/emacs.install_arch
 --with-mailutils --with-x-toolkit=gtk3 --with-xft --with-modules'

Configured features:
XPM JPEG TIFF GIF PNG RSVG SOUND GPM DBUS GSETTINGS GLIB NOTIFY INOTIFY
ACL LIBSELINUX GNUTLS LIBXML2 FREETYPE HARFBUZZ M17N_FLT LIBOTF XFT ZLIB
TOOLKIT_SCROLL_BARS GTK3 X11 XDBE XIM MODULES THREADS LIBSYSTEMD JSON
PDUMPER LCMS2 GMP

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

Major mode: C++//l

Minor modes in effect:
  electric-pair-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
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t
  abbrev-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message rmc puny dired dired-loaddefs
format-spec rfc822 mml mml-sec password-cache epa derived epg epg-config
gnus-util rmail rmail-loaddefs text-property-search time-date 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 cus-start cus-load
cc-mode cc-fonts easymenu cc-guess cc-menus cc-cmds cc-styles cc-align
cc-engine cc-vars cc-defs cl-loaddefs cl-lib term/tmux term/xterm xterm
elec-pair 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
inotify 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 77664 8509)
 (symbols 48 9388 1)
 (strings 32 23186 1893)
 (string-bytes 1 836866)
 (vectors 16 10470)
 (vector-slots 8 105810 5838)
 (floats 8 25 245)
 (intervals 56 215 0)
 (buffers 992 12))