Fwd: Crash when buffer is edited while save-buffer asks for coding system

[Glenn Morris]

Does anyone have any ideas about this? It causes a reproducible crash
(see very nice recipe below) with the current EMACS_22_BASE on
Gnu/Linux, so it would be good to fix.

It happens because when Fwrite_region calls
Vselect_safe_coding_system_function, it opens a window for the user to
modify the buffer mid-save. The abort in buf_charpos_to_bytepos in
marker.c due to changed buffer size is what causes the actual crash.

One easy solution is to for Fwrite_region to make the buffer read-only
while Vselect_safe_coding_system_function is called. That will protect
against accidental editing of the buffer at least, but of course a
determined user could still make the buffer writable again.

Ideally, I think one would want errors during write-region to abort
the write, not Emacs.


> --- Begin Message ---
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> Subject: 
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> Crash when buffer is edited while save-buffer asks for coding system
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> Date: 
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> Tue, 25 Dec 2007 01:34:00 +0100
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> User-agent: 
>
> Mozilla/5.0 (Windows; U; Windows NT 5.1; de;	rv:1.8.1.6) Gecko/20070728 Thunderbird/2.0.0.6 Mnenhy/0.7.5.0
>
>
>
>
> Please describe exactly what actions triggered the bug
> and the precise symptoms of the bug:
>
>
> Manual way:
> - emacs -Q
> - Create a new text file
> - C-x RET f windows-1252 RET
> - insert "Hi"
> - M-x ucs-insert RET 2122 RET (inserts a trademark symbol)
> - C-x C-s
> - C-x RET f latin-1 RET C-x C-s
> - Emacs will ask for a coding system, since latin-1 does not contain the
>   trademark symbol.
> - C-x C-o until point is in your file with the trademark
> - C-a C-d to delete the first character
> - C-x C-o until point is back at minibuffer
> - RET
> - "Would you like to attach a debugger?" I guess you will select Yes
>   here :)
>
> Automatic way:
>
> (progn
>   (with-current-buffer (find-file-noselect (make-temp-file
>                                             "charsetbug"))
>     (set-buffer-file-coding-system 'windows-1252)
>     (insert "Hi")
>     (ucs-insert 8482) ;; trademark sign
>     (save-buffer 0)
>     (setq buf (current-buffer))
>     (pop-to-buffer buf))
>   (set-buffer buf)
>   (set-buffer-file-coding-system 'latin-1)
>   (defun abcd () (interactive)
>     (let ((wnd (selected-window)))
>     (select-window (get-buffer-window buf))
>     (goto-char (point-min))
>     (delete-char 1)
>     (select-window wnd)
>     (execute-kbd-macro "\r")))
>   (global-set-key "\C-cq" 'abcd)
>   (execute-kbd-macro "\C-x\C-s\C-cq"))
>
> Merry Christmas! :)
>
>
>
> In GNU Emacs 22.1.1 (i386-mingw-nt5.1.2600)
>  of 2007-06-02 on RELEASE
> Windowing system distributor `Microsoft Corp.', version 5.1.2600
> configured using `configure --with-gcc (3.4) --cflags -Ic:/gnuwin32/include'
>
> Important settings:
>   value of $LC_ALL: nil
>   value of $LC_COLLATE: nil
>   value of $LC_CTYPE: nil
>   value of $LC_MESSAGES: nil
>   value of $LC_MONETARY: nil
>   value of $LC_NUMERIC: nil
>   value of $LC_TIME: nil
>   value of $LANG: DEU
>   locale-coding-system: cp1252
>   default-enable-multibyte-characters: t
>
> Major mode: Lisp Interaction
>
> Minor modes in effect:
>   encoded-kbd-mode: t
>   tooltip-mode: t
>   tool-bar-mode: t
>   mouse-wheel-mode: t
>   menu-bar-mode: t
>   file-name-shadow-mode: t
>   global-font-lock-mode: t
>   font-lock-mode: t
>   blink-cursor-mode: t
>   unify-8859-on-encoding-mode: t
>   utf-translate-cjk-mode: t
>   auto-compression-mode: t
>   line-number-mode: t
>
> Recent input:
> M-x r e p o r t - e m a c s - b u g <return>
>
> Recent messages:
> ("D:\\Progs\\emacs\\bin\\emacs.exe" "-q")
> Loading encoded-kb...done
> For information about the GNU Project and its goals, type C-h C-p. [2 times]
> Loading emacsbug...
> Loading regexp-opt...done
> Loading emacsbug...done
>
> --- End Message ---