bug#71774: 31.0.50; Hash table weakness broken?

[Eli Zaretskii]

> Date: Tue, 25 Jun 2024 15:57:55 +0200
> From:  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.

Mattias, could you perhaps look into this?  I presume the same happens
on the emacs-30 branch, which makes the fix more important.

Thanks.