bug#31978: 26.1.50; "s" in gnus *Group* error: "eieio-override-prin1: Apparently circular structure being printed"

[Tom Tromey]

I am using Gnus in Emacs 26.

When I "s" in the *Group* buffer, I sometimes get this error:

eieio-override-prin1: Apparently circular structure being printed

I got it again today, so I enabled debug-on-error and got this stack
trace.

I can't always reproduce this, but once gnus gets into this state it
seems to be stuck.  Last time, IIRC, I worked around it by removing the
registry and killing Emacs.


Debugger entered--Lisp error: (error "Apparently circular structure being 
printed")
  prin1(#<hash-table eql 4/100 0x2229a85>)
  eieio-override-prin1(#<hash-table eql 4/100 0x14cafc5>)
  #f(compiled-function (this &optional comment) "Write object THIS out to the 
current stream.\nThis writes out the vector version of this object.  Complex 
and recursive\nobject are discouraged from being written.\n  If optional 
COMMENT is non-nil, include comments when outputting\nthis object." #<bytecode 
0x56a7ed>)(#<registry-db registry-db> ";; EIEIO PERSISTENT OBJECT")
  apply(#f(compiled-function (this &optional comment) "Write object THIS out to 
the current stream.\nThis writes out the vector version of this object.  
Complex and recursive\nobject are discouraged from being written.\n  If 
optional COMMENT is non-nil, include comments when outputting\nthis object." 
#<bytecode 0x56a7ed>) (#<registry-db registry-db> ";; EIEIO PERSISTENT OBJECT"))
  #f(compiled-function (&rest cnm-args) #<bytecode 0x2229a79>)(#<registry-db 
registry-db> ";; EIEIO PERSISTENT OBJECT")
  #f(compiled-function (cl--cnm this &optional comment) "Write persistent 
object THIS out to the current stream.\nOptional argument COMMENT is a header 
line comment." #<bytecode 0x151f105>)(#f(compiled-function (&rest cnm-args) 
#<bytecode 0x2229a79>) #<registry-db registry-db> ";; EIEIO PERSISTENT OBJECT")
  apply(#f(compiled-function (cl--cnm this &optional comment) "Write persistent 
object THIS out to the current stream.\nOptional argument COMMENT is a header 
line comment." #<bytecode 0x151f105>) #f(compiled-function (&rest cnm-args) 
#<bytecode 0x2229a79>) (#<registry-db registry-db> ";; EIEIO PERSISTENT 
OBJECT"))
  #f(compiled-function (&rest args) #<bytecode 0xf219c9>)(#<registry-db 
registry-db> ";; EIEIO PERSISTENT OBJECT")
  apply(#f(compiled-function (&rest args) #<bytecode 0xf219c9>) #<registry-db 
registry-db> ";; EIEIO PERSISTENT OBJECT")
  object-write(#<registry-db registry-db> ";; EIEIO PERSISTENT OBJECT")
  #f(compiled-function (this &optional file) "Save persistent object THIS to 
disk.\nOptional argument FILE overrides the file name specified in the 
object\ninstance." #<bytecode 0x151f179>)(#<registry-db registry-db> 
"~/.gnus.registry.eieio")
  apply(#f(compiled-function (this &optional file) "Save persistent object THIS 
to disk.\nOptional argument FILE overrides the file name specified in the 
object\ninstance." #<bytecode 0x151f179>) #<registry-db registry-db> 
"~/.gnus.registry.eieio")
  eieio-persistent-save(#<registry-db registry-db> "~/.gnus.registry.eieio")
  gnus-registry-save()
  run-hooks(gnus-save-newsrc-hook)
  apply(run-hooks gnus-save-newsrc-hook)
  gnus-run-hooks(gnus-save-newsrc-hook)
  gnus-save-newsrc-file(nil)
  gnus-group-save-newsrc(nil)
  funcall-interactively(gnus-group-save-newsrc nil)
  call-interactively(gnus-group-save-newsrc nil nil)
  command-execute(gnus-group-save-newsrc)






In GNU Emacs 26.1.50 (build 5, x86_64-pc-linux-gnu, GTK+ Version 3.22.30)
 of 2018-06-25 built on pokyo
Repository revision: 826e8d1f12b014617c8899936730a740a09fefb1
Windowing system distributor 'Fedora Project', version 11.0.11906000
System Description:     Fedora release 28 (Twenty Eight)

Recent messages:
Expiring articles...done
Save the BBDB now? (y or n) y
 
Saving file /home/tromey/DotEmacs/.bbdb...
Wrote /home/tromey/DotEmacs/.bbdb
Saving Gnus registry (918 entries) to ~/.gnus.registry.eieio...
eieio-override-prin1: Apparently circular structure being printed
Quit
C-z C-g is undefined
s runs the command gnus-group-save-newsrc
Quit
Configured using:
 'configure --prefix=/home/tromey/Emacs/install --with-modules'

Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND DBUS GSETTINGS NOTIFY
LIBSELINUX GNUTLS LIBXML2 FREETYPE LIBOTF XFT ZLIB TOOLKIT_SCROLL_BARS
GTK3 X11 MODULES THREADS LIBSYSTEMD LCMS2

Important settings:
  value of $LANG: en_US.UTF-8
  value of $XMODIFIERS: @im=ibus
  locale-coding-system: utf-8-unix

Major mode: Group

Minor modes in effect:
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  gnus-topic-mode: t
  gnus-undo-mode: t
  shell-dirtrack-mode: t
  which-function-mode: t
  erc-services-mode: t
  erc-networks-mode: t
  savehist-mode: t
  tooltip-mode: t
  global-eldoc-mode: t
  electric-indent-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
  transient-mark-mode: t

Load-path shadows:
/home/tromey/.emacs.d/elpa/bubbles-0.5/bubbles hides 
/home/tromey/Emacs/install/share/emacs/26.1.50/lisp/play/bubbles

Features:
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vc-svn vc-cvs vc-rcs sort gnus-cite smiley shr-color shr svg dom
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netrc nnoo gnus-spec gnus-int gnus-range message rmc puny rfc822 mml
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make-network-process emacs)

Memory information:
((conses 16 1316874 39038)
 (symbols 48 104412 2)
 (miscs 40 24587 955)
 (strings 32 344935 31498)
 (string-bytes 1 8232441)
 (vectors 16 122264)
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 (buffers 992 35))