bug#23651: 25.1.50; edebug-read-sexp: infinite recursion when reading backquote or comma

bug#23651: 25.1.50; edebug-read-sexp: infinite recursion when reading backquote or comma

[ju.schmidt]

Start emacs with -Q, do M-: and type "(require 'edebug)". Then write
this in buffer "*scratch*":

`1

Then do M-: and type "(edebug-eval-defun)". It will give this error:

"edebug-read-sexp: Lisp nesting exceeds `max-lisp-eval-depth'"

(The documentation for edebug-eval-defun says that this should display
"1" instead of giving an error).

One gets the same error when the buffer contains this instead:

,1

This is caused by an endless recursion in edebug-read-sexp which
apparently can be fixed like this:

diff --git a/lisp/emacs-lisp/edebug.el b/lisp/emacs-lisp/edebug.el
index c283c16..4254862 100644
--- a/lisp/emacs-lisp/edebug.el
+++ b/lisp/emacs-lisp/edebug.el
@@ -722,9 +722,9 @@ edebug-read-sexp
      ((eq class 'string) (read (current-buffer)))
      ((eq class 'quote) (forward-char 1)
       (list 'quote (edebug-read-sexp)))
-     ((eq class 'backquote)
+     ((eq class 'backquote) (forward-char 1)
       (list '\` (edebug-read-sexp)))
-     ((eq class 'comma)
+     ((eq class 'comma) (forward-char 1)
       (list '\, (edebug-read-sexp)))
      (t ; anything else, just read it.
       (read (current-buffer))))))

Configured using:
 'configure --prefix=/home/jhs/local --with-xpm=no --with-gif=no
 --with-tiff=no PKG_CONFIG_PATH=/home/jhs/local/lib/pkgconfig'

Configured features:
JPEG PNG SOUND DBUS GSETTINGS NOTIFY LIBXML2 FREETYPE XFT ZLIB
TOOLKIT_SCROLL_BARS GTK3 X11

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
  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

Load-path shadows:
None found.

Features:
(shadow sort map mail-extr emacsbug message puny seq byte-opt gv
bytecomp byte-compile cl-extra help-mode cconv cl-loaddefs pcase cl-lib
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 sendmail rfc2047 rfc2045 ietf-drums mm-util mail-prsvr
mail-utils term/xterm xterm 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 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 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 charscript 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 dbusbind inotify dynamic-setting
system-font-setting font-render-setting move-toolbar gtk x-toolkit x
multi-tty make-network-process emacs)

Memory information:
((conses 16 98461 8207)
 (symbols 48 20696 0)
 (miscs 40 33 93)
 (strings 32 17428 3931)
 (string-bytes 1 532970)
 (vectors 16 11481)
 (vector-slots 8 395373 4073)
 (floats 8 185 220)
 (intervals 56 207 0)
 (buffers 976 11)
 (heap 1024 33354 1491))

bug#23651: 25.1.50; edebug-read-sexp: infinite recursion when reading backquote or comma

[npostavs]

tags 23651 fixed
close 23651 26.1
quit

ju.schmidt@gmx.de writes:

> Start emacs with -Q, do M-: and type "(require 'edebug)". Then write
> this in buffer "*scratch*":
>
> `1
>
> Then do M-: and type "(edebug-eval-defun)". It will give this error:
>
> "edebug-read-sexp: Lisp nesting exceeds `max-lisp-eval-depth'"
>
> (The documentation for edebug-eval-defun says that this should display
> "1" instead of giving an error).
>
> One gets the same error when the buffer contains this instead:
>
> ,1
>
> This is caused by an endless recursion in edebug-read-sexp which
> apparently can be fixed like this:

Pushed to master [1: 5f6ef7cba8].

1: 2017-03-25 14:38:29 -0400 5f6ef7cba8200d19198e42a9a76fef1618b5f233
  Stop edebug getting stuck on backquote (Bug#23651)