Re: Unrecoverable data loss

[martin rudalics]

> 5. The inserted text retains the properties in buffer A that it has in
> the *Help* buffer, in particular clickable links.  Click on the link
> displaying the value of the preferred charset, or, if there are text
> properties in the description, you can click on one of these links.
> (Clicking the link of the value of the code point, or the button
> labelled "customize what to show" does not produce the problem.)
>
> 6. Now buffer A is in Help mode and contains only the Help text of the
> clicked link; the text you had previously type is gone.  If you type
> C-_, Emacs beeps and says "Buffer is read-only".  If you toggle the
> read-only status and type C-_ again, Emacs beeps again and says "No undo
> information in this buffer".  If you were typing in a buffer that does
> not have auto-save, its contents prior to step 5 is AFAICT unrecoverably
> lost.

`describe-character-set' uses

    (with-output-to-temp-buffer (help-buffer)

where `help-buffer' is defined as

(defun help-buffer ()
  (buffer-name                          ;for with-output-to-temp-buffer
   (if help-xref-following
       (current-buffer)
     (get-buffer-create "*Help*"))))

hence turning your current buffer into a help buffer thus clearing its
contents and undo-list, making it read-only, ...

Maybe `help-buffer' should refuse to return a buffer if it is not
read-only, `buffer-undo-list' is not t, ...