bug#3578: 23.0.94; when saving some files, diff does not work

Please write in English if possible, because the Emacs maintainers
usually do not have translators to read other languages for them.

Your bug report will be posted to the [email protected] mailing list.

Please describe exactly what actions triggered the bug
and the precise symptoms of the bug:

I start emacs with -q and -no-site-file, visit some file, make some
changes, switch to buffer "scratch" (or any other buffer with no
associated file) and run save-some-buffers. It asks me what to do with
the visited file, and I want to view the diff, so I press "d".  And I
get an error message: "Not applicable: no file."

I believe that the problem was introduced by revision 1.985 of files.el,
line 4178, that says:

(if (null buffer-file-name)

and should say:

(if (null buffer-file-name buf)

Thanks,

Tiago Saboga.

If Emacs crashed, and you have the Emacs process in the gdb debugger,
please include the output from the following gdb commands:
    `bt full' and `xbacktrace'.
If you would like to further debug the crash, please read the file
/usr/share/emacs/23.0.94/etc/DEBUG for instructions.


In GNU Emacs 23.0.94.1 (x86_64-pc-linux-gnu, GTK+ Version 2.16.1)
 of 2009-05-25 on elegiac, modified by Debian
 (emacs-snapshot package, version 1:20090525-1)
Windowing system distributor `The X.Org Foundation', version 11.0.10402000
configured using `configure  '--build' 'x86_64-linux-gnu' '--host' 'x86_64-linux-gnu' '--prefix=/usr' '--sharedstatedir=/var/lib' '--libexecdir=/usr/lib' '--localstatedir=/var' '--infodir=/usr/share/info' '--mandir=/usr/share/man' '--with-pop=yes' '--enable-locallisppath=/etc/emacs-snapshot:/etc/emacs:/usr/local/share/emacs/23.0.94/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/23.0.94/site-lisp:/usr/share/emacs/site-lisp' '--with-x=yes' '--with-x-toolkit=gtk' 'build_alias=x86_64-linux-gnu' 'host_alias=x86_64-linux-gnu' 'CFLAGS=-DDEBIAN -DSITELOAD_PURESIZE_EXTRA=5000 -g -O2' 'LDFLAGS=-g -Wl,--as-needed' 'CPPFLAGS=''

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: pt_BR.UTF-8
  value of $XMODIFIERS: nil
  locale-coding-system: utf-8-unix
  default-enable-multibyte-characters: t

Major mode: Alunos

Minor modes in effect:
  show-paren-mode: t
  display-time-mode: t
  tooltip-mode: t
  mouse-wheel-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  global-auto-composition-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  column-number-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent messages:
Saving /home/tiago/.newsrc.eld...
Saving file /home/tiago/.newsrc.eld...
Wrote /home/tiago/.newsrc.eld
Saving /home/tiago/.newsrc.eld...done