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Re: Info-mode patch


From: Eli Zaretskii
Subject: Re: Info-mode patch
Date: Mon, 03 Jul 2023 20:07:25 +0300

> From: Arthur Miller <arthur.miller@live.com>
> Cc: Juri Linkov <juri@linkov.net>,  emacs-devel@gnu.org
> Date: Mon, 03 Jul 2023 00:43:15 +0200
> 
> By the way, as a last thing, is this a bug (found it while I was parsing
> Info-mode-map and generated wrappers for commands in it some time ago):
> 
> (insert (pp Info-mode-map))
> 
> (keymap
>  #^[nil nil keymap
>       #^^[3 0 nil nil nil nil nil nil nil nil nil Info-next-reference nil nil 
> nil Info-follow-nearest-node nil nil nil nil nil nil nil nil nil nil nil nil 
> nil
>       
> I have removed rest of printed code for the brewity for the mail, but if you
> eval above and place the cursor somewhere after the "keymap", or before the 
> char
> table, and then try to read the subtype with:
> 
> (char-table-subtype (read (current-buffer)))
> 
> Then Emacs dumps core in version 26 up to current master. Emacs 25 actually 
> ends
> up in debugger instead of crashing:

(It is not a crash, it's abort.)

Please report a bug with all these details.

AFAICT, this happens because the debugger now uses cl-print to display
objects in the backtrace, and cl-print calls type-of, which aborts if
presented with a sub-char-table:

        /* "Impossible" cases.  */
        case PVEC_MISC_PTR:
        case PVEC_OTHER:
        case PVEC_SUB_CHAR_TABLE:
        case PVEC_FREE: ;
        }
      emacs_abort ();



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