Dear Maintainer,

*** Reporter, please consider answering these questions, where appropriate ***

   * What led up to the situation?

Attempt to exit from Gnus gives:

Debugger entered--Lisp error: (error "Apparently circular structure being
printed")
  prin1(#<hash-table eql 4/100 0x469f219>)
  eieio-override-prin1(#<hash-table eql 4/100 0x185729d>)
  #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
0x4e2bed>)(#<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 0x4e2bed>) (#<registry-db registry-db> ";; EIEIO PERSISTENT
OBJECT"))
  #f(compiled-function (&rest cnm-args) #<bytecode 0x3b190d9>)(#<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 0x150e4b1>)(#f(compiled-function (&rest cnm-args)
#<bytecode 0x3b190d9>) #<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 0x150e4b1>) #f(compiled-function (&rest cnm-args)
#<bytecode 0x3b190d9>) (#<registry-db registry-db> ";; EIEIO PERSISTENT
OBJECT"))
  #f(compiled-function (&rest args) #<bytecode 0x38465e1>)(#<registry-db
registry-db> ";; EIEIO PERSISTENT OBJECT")
  apply(#f(compiled-function (&rest args) #<bytecode 0x38465e1>) #<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 0x150e4e5>)(#<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 0x150e4e5>) #<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()
  gnus-group-exit()
  funcall-interactively(gnus-group-exit)
  #<subr call-interactively>(gnus-group-exit nil nil)
  apply(#<subr call-interactively> gnus-group-exit (nil nil))
  call-interactively@ido-cr+-record-current-command(#<subr call-interactively>
gnus-group-exit nil nil)
  apply(call-interactively@ido-cr+-record-current-command #<subr call-
interactively> (gnus-group-exit nil nil))
  call-interactively(gnus-group-exit nil nil)
  command-execute(gnus-group-exit)

   * What was the outcome of this action?

The above backtrace.

   * What outcome did you expect instead?

Normal exit from Gnus and Emacs.

I've found the following bug report upstream:

http://emacs.1067599.n8.nabble.com/bug-31978-26-1-50-quot-s-quot-in-gnus-Group-
error-quot-eieio-override-prin1-Apparently-circular-stru-td459075.html

which says that apparently the problem is solved in 26.2, but unfortunately
that's not what is present in Buster, so maybe 26.2 should be considered?


Sincerely,
Gour