bug#71774: 31.0.50; Hash table weakness broken?

[martin rudalics via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

With Emacs -Q evaluate the following forms in *scratch* step by step:


(defvar table (make-hash-table :weakness t))

(puthash t (split-window) table)

(delete-other-windows)

(garbage-collect)

(gethash t table)


The last form evaluates to #<window 7> here.  In all prior Emacs
versions I have it evaluates to nil.  IIUC this means that either hash
table weakness is broken or there is a bug in the collector.  To exclude
that the behavior is specific to the window handling code, note that the
recipe you can find here

https://nullprogram.com/blog/2012/12/17/

is now broken too.


In GNU Emacs 31.0.50 (build 2, x86_64-pc-linux-gnu, GTK+ Version
  3.24.38, cairo version 1.16.0) of 2024-06-25 built on restno
Repository revision: b9da5ee06f2e4ae807336dd6a641ae797831d097
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12101007
System Description: Debian GNU/Linux 12 (bookworm)

Configured using:
  'configure --with-gif=ifavailable --with-tiff=ifavailable
  --with-gnutls=no --without-pop --enable-gcc-warnings=warn-only
  --enable-checking=yes,glyphs,structs
  --enable-check-lisp-object-type=yes 'CFLAGS=-O0 -g3 -no-pie
  -Wno-missing-braces''

Configured features:
CAIRO DBUS FREETYPE GIF GLIB GSETTINGS HARFBUZZ JPEG LIBSELINUX MODULES
NOTIFY INOTIFY PDUMPER PNG SECCOMP SOUND THREADS TIFF
TOOLKIT_SCROLL_BARS WEBP X11 XDBE XIM XINPUT2 XPM GTK3 ZLIB

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

Major mode: Lisp Interaction

Minor modes in effect:
   tooltip-mode: t
   global-eldoc-mode: t
   eldoc-mode: t
   show-paren-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
   blink-cursor-mode: t
   minibuffer-regexp-mode: t
   line-number-mode: t
   indent-tabs-mode: t
   transient-mark-mode: t
   auto-composition-mode: t
   auto-encryption-mode: t
   auto-compression-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message mailcap yank-media puny dired
dired-loaddefs rfc822 mml mml-sec password-cache epa derived epg rfc6068
epg-config gnus-util text-property-search time-date subr-x mm-decode
mm-bodies mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader
cl-loaddefs cl-lib sendmail rfc2047 rfc2045 ietf-drums mm-util
mail-prsvr mail-utils rmc iso-transl tooltip cconv eldoc paren electric
uniquify ediff-hook vc-hooks lisp-float-type elisp-mode mwheel
term/x-win x-win term/common-win x-dnd touch-screen tool-bar dnd fontset
image regexp-opt fringe tabulated-list replace newcomment text-mode
lisp-mode prog-mode register page tab-bar menu-bar rfn-eshadow isearch
easymenu timer select scroll-bar mouse jit-lock font-lock syntax
font-core term/tty-colors frame minibuffer nadvice seq simple cl-generic
indonesian philippine 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
composite emoji-zwj charscript charprop case-table epa-hook
jka-cmpr-hook help abbrev obarray oclosure cl-preloaded button loaddefs
theme-loaddefs faces cus-face macroexp files window text-properties
overlay sha1 md5 base64 format env code-pages mule custom widget keymap
hashtable-print-readable backquote threads dbusbind inotify
dynamic-setting system-font-setting font-render-setting cairo gtk
x-toolkit xinput2 x multi-tty move-toolbar make-network-process emacs)

Memory information:
((conses 16 39683 9012) (symbols 48 5369 0) (strings 32 12780 1387)
  (string-bytes 1 312604) (vectors 16 9423)
  (vector-slots 8 113146 8563) (floats 8 25 29) (intervals 56 255 0)
  (buffers 984 11))