bug#7033: 23.2; M-n in diff mode causes unwanted face changes

[Stefan Monnier <monnier@IRO.UMontreal.CA>]

> When I open almost any patch in the diff mode and press M-n to get to
> the next hunk, random portions of the text (just parts of a line) change
> their face from diff-added or diff-removed to diff-refine change.  This
> causes the text to be displayed in a wrong background, causing it to be
> rather difficult to read (and is always unpleasant).  I have not
> observed any pattern as to what text is changed but it is always exactly
> the same text in the given file.

> This does not happen with emacs 22, only with 23, I have observeed it on
> Suse and Debian linux distributions.  I can reproduce the bug when I run
> emacs with the -Q switch like e.g.

It's not a bug, it's a feature (the diff-refine face is used to
highlight the parts of a hunk that are changed, at a finer granularity
than just lines).  So when the hunk looks like:

   -foo bar baz
   +foo toto bar baz

the "toto" word will be highlighted.  When diffing refilled LaTeX
paragraphs where a few words were added/removed, I find it to be invaluable.

C-h f diff-auto-refine-mode RET
C-h f diff-refine-hunk RET


        Stefan