bug#29756: 25.2; Footnote-mode: recursive footnotes [PATCH included]

[Boruch Baum]

The current behavior of `Footnote-mode' allows recursive footnotes, in
the sense that one can create a footnote inside another footnote. The
attached suggestion for a patch merely checks that (point) is prior to
the point of the first footnote before allowing another footnote to be
created.

REPRODUCE THE BUG BEHAVIOR
==========================
1] Enter random text.
2] M-x footnote-mode
3] C-c ! a
4] Observe that emacs has generated a footnote and that point is there.
Optionally, now enter random footnote text.
5] C-c ! a
6] Observe that emacs has create a new footnote, within the current
footnote!


PROPOSED SOLUTION
=================
This snippet is presented as an advice because that's how I'm dealing
with it on my personal install, but of course the project would just
perform the check within `Footnote-add-footnote'.

(defadvice Footnote-add-footnote (around abort-when-in-fn-area activate)
  (interactive)
  (if (or
        (not footnote-text-marker-alist)
        (< (point) (cdr (first footnote-text-marker-alist))))
    ad-do-it
   (message "Add footnotes only while in text body")))


VERSION INFORMATION
===================
In GNU Emacs 25.2.2 (x86_64-pc-linux-gnu, GTK+ Version 3.22.20)
 of 2017-09-11, modified by Debian built on trouble
System Description:     Devuan GNU/Linux 1.0 (jessie)

Configured using:
 'configure --build x86_64-linux-gnu --prefix=/usr
 --sharedstatedir=/var/lib --libexecdir=/usr/lib
 --localstatedir=/var/lib --infodir=/usr/share/info
 --mandir=/usr/share/man --with-pop=yes
 
--enable-locallisppath=/etc/emacs25:/etc/emacs:/usr/local/share/emacs/25.2/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/25.2/site-lisp:/usr/share/emacs/site-lisp
 --with-sound=alsa --without-gconf --build x86_64-linux-gnu
 --prefix=/usr --sharedstatedir=/var/lib --libexecdir=/usr/lib
 --localstatedir=/var/lib --infodir=/usr/share/info
 --mandir=/usr/share/man --with-pop=yes
 
--enable-locallisppath=/etc/emacs25:/etc/emacs:/usr/local/share/emacs/25.2/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/25.2/site-lisp:/usr/share/emacs/site-lisp
 --with-sound=alsa --without-gconf --with-x=yes --with-x-toolkit=gtk3
 --with-toolkit-scroll-bars 'CFLAGS=-g -O2
 -fdebug-prefix-map=/build/emacs25-XrMyQe/emacs25-25.2+1=.
 -fstack-protector-strong -Wformat -Werror=format-security -Wall'
 'CPPFLAGS=-Wdate-time -D_FORTIFY_SOURCE=2' LDFLAGS=-Wl,-z,relro'

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

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

Major mode: Messages

Minor modes in effect:
  global-company-mode: t
  company-mode: t
  ivy-mode: t
  sr-popviewer-mode: t
  recentf-mode: t
  shell-dirtrack-mode: t
  winner-mode: t
  show-paren-mode: t
  savehist-mode: t
  desktop-save-mode: t
  global-undo-tree-mode: t
  undo-tree-mode: t
  delete-selection-mode: t
  tooltip-mode: t
  global-eldoc-mode: t
  mouse-wheel-mode: t
  tool-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
  buffer-read-only: t
  size-indication-mode: t
  column-number-mode: t
  line-number-mode: t
  transient-mark-mode: t

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