bug#20075: 24.3; json.el functions are recursive

bug#20075: 24.3; json.el functions are recursive

[sindikat]

Feature request: rewrite `json.el' so that it doesn't use recursive
functions. Emacs doesn't support TCO, therefore invoking `json.el'
functions on huge data structures results in stack overflow.

For example, I created a ridiculously huge data structure using a
function from `dash.el':

(defvar a (-iterate (lambda (x) (cons x (list (list x)))) 1 5))

Now (json-encode lol) will result in exceeding `max-lisp-eval-depth'.


In GNU Emacs 24.3.1 (x86_64-pc-linux-gnu, GTK+ Version 3.10.9)
 of 2014-06-06 on brownie, modified by Debian
Windowing system distributor `The X.Org Foundation', version 11.0.11600000
System Description:	Ubuntu 14.10

Configured using:
 `configure '--build' 'x86_64-linux-gnu' '--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/emacs24:/etc/emacs:/usr/local/share/emacs/24.3/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/24.3/site-lisp:/usr/share/emacs/site-lisp'
 '--with-crt-dir=/usr/lib/x86_64-linux-gnu' '--with-x=yes'
 '--with-x-toolkit=gtk3' '--with-toolkit-scroll-bars'
 'build_alias=x86_64-linux-gnu' 'CFLAGS=-g -O2 -fstack-protector
 --param=ssp-buffer-size=4 -Wformat -Werror=format-security -Wall'
 'LDFLAGS=-Wl,-Bsymbolic-functions -Wl,-z,relro'
 'CPPFLAGS=-D_FORTIFY_SOURCE=2''

Important settings:
  value of $LC_MONETARY: kk_KZ.UTF-8
  value of $LC_NUMERIC: kk_KZ.UTF-8
  value of $LC_TIME: kk_KZ.UTF-8
  value of $LANG: en_US.UTF-8
  value of $XMODIFIERS: @im=ibus
  locale-coding-system: utf-8-unix
  default enable-multibyte-characters: t

Major mode: Help

Minor modes in effect:
  shell-dirtrack-mode: t
  icomplete-mode: t
  global-hl-line-mode: t
  show-paren-mode: t
  ido-everywhere: t
  keyfreq-autosave-mode: t
  keyfreq-mode: t
  global-undo-tree-mode: t
  undo-tree-mode: t
  override-global-mode: t
  tooltip-mode: t
  mouse-wheel-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
  column-number-mode: t
  line-number-mode: t
  global-visual-line-mode: t
  visual-line-mode: t
  transient-mark-mode: t

Recent input:
M-i M-i ) M-H <return> M-p M-N M-N M-N M-N M-n C-M-SPC 
<backspace> <backspace> SPC n i l M-H <return> 1 SPC 
( 1 ) M-h <M-backspace> <M-backspace> M-H SPC 1 SPC 
<backspace> <backspace> ( 1 SPC ( 1 ) ) SPC ( 1 SPC 
( 1 SPC ( 1 ) ) ) M-h M-SPC M-H M-x c o n s SPC ( <backspace> 
M-h ( M-H 1 SPC ( l i s t SPC 1 ) ) <return> M-p M-N 
M-N M-N M-n M-i M-i M-i ( l i s t SPC M-H ) <return> 
M-p M-h M-p M-p M-N M-N M-p M-p M-p M-p M-p M-p M-p 
M-p M-p M-N M-N M-N M-N M-n ( l i s t SPC M-I M-i M-i 
) M-H <return> M-p M-h ( l a s t SPC M-H ) <return> 
M-p M-n M-n <backspace> 1 0 0 0 M-h ( s <backspace> 
d e f v a M-s s e t q SPC l o l SPC M-H ) <return> 
M-p M-h M-I M-i M-t M-s d e f v a <backspace> <backspace> 
c o n s t SPC l o l M-H <return> ( c a r SPC l o l 
) <return> M-: ( c a r SPC l o l ) <return> ( j s o 
n - e n d <backspace> c <tab> SPC l o l ) <return> 
M-u M-u M-u M-u M-u M-u M-u M-u M-u M-u M-u M-u M-u 
M-u M-u M-u M-u M-u M-u M-u M-u M-u M-u M-u M-u M-u 
M-i M-e <help-echo> <down-mouse-1> <mouse-1> <help-echo> 
M-SPC M-H M-c M-r M-a b u <backspace> <backspace> e 
m a c - <backspace> s - b u <backspace> <backspace> 
r e p <tab> C-g C-g M-a r e p o r t <tab> <return>

Recent messages:
History item: 6
History item: 7
History item: 8
History item: 9
History item: 10
History item: 11
History item: 12
History item: 1 [3 times]
((((... ...) (...)) ((... ...))) (((... ...) (...))))
Mark set
Quit [2 times]

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env code-pages mule custom widget hashtable-print-readable backquote
make-network-process dbusbind dynamic-setting system-font-setting
font-render-setting move-toolbar gtk x-toolkit x multi-tty emacs)

bug#20075: 24.3; json.el functions are recursive

[Lars Ingebrigtsen]

Dmitry Gutov <dgutov@yandex.ru> writes:

> On 03/10/2015 11:35 PM, sindikat@mail36.net (sindikat@mail36.net) wrote:
>> Feature request: rewrite `json.el' so that it doesn't use recursive
>> functions. Emacs doesn't support TCO, therefore invoking `json.el'
>> functions on huge data structures results in stack overflow.
>>
>> For example, I created a ridiculously huge data structure using a
>> function from `dash.el':  ...
>
> Have you seen this to be an actual problem in practice?

There was no response to this.  However, Emacs has in recent years
gotten support for libjansson to parse JSON, so this issue shouldn't be
relevant any more, and I'm closing this bug report.

(And if it is, I think the work-around is to increase max-specpdl-size
around the json.el functions.)

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no