In Diff mode, M-/ runs diff-undo. It should do dynamic completion, the same as everywhere else.
In GNU Emacs 24.3.50.1 (i386-mingw-nt6.2.9200)
of 2013-03-22 on MACHINE
Bzr revision: 112110
dengste@eml.cc-20130322193115-9pi2k2te7nhmajgxWindowing system distributor `Microsoft Corp.', version 6.2.9200
Configured using:
`configure --with-gcc (4.7) --cflags -I c:/gnuwin32/include --ldflags
-L c:/gnuwin32/lib'
Important settings:
value of $LANG: ENG
locale-coding-system: cp1252
default enable-multibyte-characters: t
Major mode: Diff
Minor modes in effect:
diff-auto-refine-mode: t
tooltip-mode: t
mouse-wheel-mode: t
tool-bar-mode: t
menu-bar-mode: t
file-name-shadow-mode: t
global-font-lock-mode: t
font-lock-mode: t
blink-cursor-mode: t
auto-composition-mode: t
auto-encryption-mode: t
auto-compression-mode: t
line-number-mode: t
transient-mark-mode: t
Recent input:
b u f M-/ M-x d i f f - m o d e <return> M-/ M-x r
e p o r t - e m a c s - b u g <return>
Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
Undo!
Load-path shadows:
None found.
Features:
(shadow sort gnus-util mail-extr emacsbug message format-spec rfc822 mml
mml-sec mm-decode mm-bodies mm-encode mail-parse rfc2231 mailabbrev
gmm-utils mailheader sendmail rfc2047 rfc2045 ietf-drums mm-util
mail-prsvr mail-utils diff-mode easymenu easy-mmode dabbrev time-date
tooltip ediff-hook vc-hooks lisp-float-type mwheel dos-w32 ls-lisp
w32-common-fns disp-table w32-win w32-vars tool-bar dnd fontset image
regexp-opt fringe tabulated-list newcomment lisp-mode register page
menu-bar rfn-eshadow timer select scroll-bar mouse jit-lock font-lock
syntax facemenu font-core frame cham georgian utf-8-lang misc-lang
vietnamese tibetan thai tai-viet lao korean japanese hebrew greek
romanian slovak czech european ethiopic indian cyrillic chinese
case-table epa-hook jka-cmpr-hook help simple abbrev minibuffer button
faces cus-face macroexp files text-properties overlay sha1 md5 base64
format env code-pages mule custom widget hashtable-print-readable
backquote make-network-process w32notify w32 multi-tty emacs)