bug#15190: 24.3; Reader error when combining print-circle and hash tables

[Christopher Wellons]

I'm running into an issue in Emacs 24.3 where the lisp reader fails to
parse hash tables printed with print-circle set to t.

(let ((print-circle t)
      (table (make-hash-table)))
  (puthash t table table) ; recursive
  (read-from-string (prin1-to-string table)))
;; => sequencep error!

Or more succinctly:

(read-from-string "#1=#s(hash-table)")

The same error occurs not just with a direct reference, but also if the
hash table is anywhere inside a referenced data structure.

(read-from-string "#1=[#s(hash-table)]")
(read-from-string "#1=(#s(hash-table))")

I came across this problem trying to store a set of circular-referenced
hash tables to a file.


In GNU Emacs 24.3.1 (x86_64-pc-linux-gnu, GTK+ Version 3.8.2)
 of 2013-06-25 on sochi, modified by Debian
Windowing system distributor `The X.Org Foundation', version 11.0.11204000
System Description:     Debian GNU/Linux unstable (sid)

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,-z,relro' 'CPPFLAGS=-D_FORTIFY_SOURCE=2''

Important settings:
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix
  default enable-multibyte-characters: t

Major mode: Message

Minor modes in effect:
  shell-dirtrack-mode: t
  mml-mode: t
  diff-auto-refine-mode: t
  yas-global-mode: t
  yas-minor-mode: t
  ido-ubiquitous-mode: t
  ido-everywhere: t
  show-paren-mode: t
  winner-mode: t
  display-time-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
  auto-fill-function: message-do-auto-fill
  transient-mark-mode: t
  abbrev-mode: t

Recent input:
<left> <left> <left> <left> <left> <left> <left> <left>
<left> <left> <backspace> ( M-> <return> C-x C-s M-<
M-> M-< M-> M-< <down> <down> <down> <down> <down>
<down> <down> <down> <down> <down> <down> C-e <left>
M-$ M-> M-x i s <return> i i i a i y <up> <up> <up>
<up> <up> <up> <up> <up> <up> <up> <up> <right> <right>
<right> <down> <left> ! <right> C-x C-s <down> <down>
<down> <down> M-> <left> <left> <left> <left> <left>
<left> <left> <left> <left> <left> <left> <left> <left>
<left> <left> <left> <left> <left> <down> <down> <up>
<up> <up> <up> <backspace> / <up> <backspace> <down>
<up> SPC <down> <backspace> . <up> <right> <right>
<right> <right> <right> <right> SPC n o t SPC u s <backspace>
<backspace> j u s t SPC w i t h SPC a SPC d i r e c
t SPC r <backspace> r e f e r n e c e , SPC b u t SPC
a l s o M-q C-x C-s M-> <up> <up> <up> <up> <left>
<down> <left> <down> <down> <down> <down> <down> <left>
C-x C-e <up> C-e C-x C-e M-> C-x C-s M-< M-> <up> <up>
<up> <up> <up> <up> <up> <up> <down> <down> <down>
<down> <down> <down> <down> <down> <down> <down> <down>
<up> <up> <up> <up> <up> <up> <left> SPC ; e r r <backspace>
<backspace> <backspace> SPC e r r o r M-> C-x C-s <up>
<up> <up> <up> <up> <up> <left> <M-backspace> <backspace>
<backspace> <backspace> C-x C-s M-> M-x <return> 0
C-x C-s C-x C-g C-x C-f / / t m p / m a i l <backspace>
<backspace> <backspace> <backspace> r e p o r t <return>
<return> M-x i n s C-s C-s C-s <return> <return> C-x
C-s C-x b <return> M-x r e p o r t - <return>

Recent messages:
Wrote /home/wellons/*message*-20130826-005023
Mark set
Spell-checking *unsent mail* using aspell with default dictionary...done
Saving file /home/wellons/*message*-20130826-005023...
Wrote /home/wellons/*message*-20130826-005023
(New file)
Mark set
Saving file /tmp/report...
Wrote /tmp/report
Undo!

Load-path shadows:
/home/wellons/.emacs.d/elpa/magit-20130822.712/.dir-locals hides 
/home/wellons/.emacs.d/elpa/pkg-info-20130817.2334/.dir-locals
/home/wellons/.emacs.d/elpa/batch-mode-20110113.952/batch-mode hides 
~/.emacs.d/etc/batch-mode
/usr/share/emacs/24.3/site-lisp/debian-startup hides 
/usr/share/emacs/site-lisp/debian-startup
/usr/share/emacs24/site-lisp/dictionaries-common/flyspell hides 
/usr/share/emacs/24.3/lisp/textmodes/flyspell
/usr/share/emacs24/site-lisp/dictionaries-common/ispell hides 
/usr/share/emacs/24.3/lisp/textmodes/ispell
/home/wellons/.emacs.d/elpa/magit-20130822.712/.dir-locals hides 
/usr/share/emacs/24.3/lisp/gnus/.dir-locals

Features:
(shadow mail-extr emacsbug sendmail sort tramp-cache tramp tramp-compat
tramp-loaddefs shell pcomplete cus-start cus-load email-setup notmuch
notmuch-parser notmuch-message notmuch-maildir-fcc notmuch-hello
notmuch-show notmuch-print notmuch-crypto notmuch-mua notmuch-address
notmuch-wash coolj notmuch-query goto-addr icalendar diary-lib
diary-loaddefs cal-menu calendar cal-loaddefs notmuch-tag crm
notmuch-lib message format-spec rfc822 mml mailabbrev gmm-utils
mailheader mm-view mml-smime mml-sec smime dig mm-decode mm-bodies
mm-encode ispell nxml-uchnm rng-xsd xsd-regexp rng-cmpct rng-nxml
rng-valid rng-loc rng-uri rng-parse nxml-parse rng-match rng-dt rng-util
rng-pttrn nxml-ns nxml-mode nxml-outln nxml-rap nxml-util nxml-glyph
nxml-enc xmltok mc-edit-lines multiple-cursors-core rect youtube-dl-mode
hyperspec thingatpt mule-util two-column find-func term ehelp electric
shr-color color etags sh-script smie executable debug jka-compr gnutls
view url-queue wid-edit timezone parse-time mail-utils network-stream
starttls url-http tls mail-parse rfc2231 rfc2047 rfc2045 ietf-drums
url-gw url-cache url-auth url url-proxy url-privacy url-expand
url-methods url-history url-cookie url-domsuf mailcap dabbrev
magit-cherry magit-bisect magit-key-mode magit grep epa derived epg
epg-config diff-mode easy-mmode git-commit-mode magit-compat hl-line
feed-setup elfeed disp-table misearch multi-isearch vc-git xml shr
browse-url xml-query dired-aux dired server paredit slime-autoloads init
batch-mode compile-bind yasnippet help-mode wombat-theme smex
ido-ubiquitous ido bracket-face parenface paren warnings skewer-setup
skewer-mode cache-table js2-mode cc-mode cc-fonts cc-guess cc-menus
cc-styles cc-align cc-cmds cc-engine cc-vars cc-defs imenu jekyll
uuid-simple simple-httpd url-util url-parse auth-source eieio byte-opt
bytecomp byte-compile cconv gnus-util time-date mm-util mail-prsvr
password-cache url-vars pp windmove winner uniquify advice help-fns
advice-preload whitespace-cleanup whitespace time utility extras edmacro
kmacro imgur json batch-mode-autoloads glsl-mode-autoloads
graphviz-dot-mode-autoloads ido-ubiquitous-autoloads
impatient-mode-autoloads htmlize-autoloads inf-ruby-autoloads inf-ruby
ruby-mode compile comint ansi-color ring javadoc-lookup-autoloads
lua-mode-autoloads magit-autoloads info easymenu
git-rebase-mode-autoloads git-commit-mode-autoloads
markdown-mode-autoloads memoize-autoloads multiple-cursors-autoloads
notmuch-autoloads nrepl-autoloads clojure-mode-autoloads
paredit-autoloads parenface-autoloads pkg-info-autoloads dash-autoloads
rdp-autoloads s-autoloads skewer-mode-autoloads js2-mode-autoloads
finder-inf simple-httpd-autoloads smex-autoloads yasnippet-autoloads
package-helper cl-macs gv cl cl-lib package tooltip ediff-hook vc-hooks
lisp-float-type mwheel x-win x-dnd tool-bar dnd fontset image regexp-opt
fringe tabulated-list newcomment lisp-mode register page menu-bar
rfn-eshadow timer select scroll-bar mouse jit-lock font-lock syntax
facemenu font-core frame cham georgian utf-8-lang misc-lang vietnamese
tibetan thai tai-viet lao korean japanese hebrew greek romanian slovak
czech european ethiopic indian cyrillic chinese case-table epa-hook
jka-cmpr-hook help simple abbrev minibuffer loaddefs button faces
cus-face macroexp files text-properties overlay sha1 md5 base64 format
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)