Re: Unrecoverable data loss

[martin rudalics <rudalics@gmx.at>]

 > 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, ...