Hi,
I have turned on which-func-mode, so that in some major
modes the function name is displayed in the mode line. Unfortunately,
the default for the variable which-func-modes (in wile which-func.el)
includes diff-mode.
I say unfortunately, since when I visit a file with a patch
(and not having the source handy), in order to display the function
name it needs to visit the file, and since it can't figure out the file
name, it pops us a file chooser box asking me for the file -- or allows
me to cancel. However, as soon as I cancel, the box pops up again --
over and over again (I think there is an event timer associated with
mode line display, once every few seconds, and these requests stack
up).