Matthias Meulien <orontee@gmail.com> writes:

> My first impression is that setting `outline-level' to
> `diff--outline-level' inconditionnaly should work but since I don't
> understand why `diff-outline-regex' hasn't been defined in terms of
> `diff-file-header-re' and `diff-hunk-header-re' I guess I am missing
> some subtleties.
>
> (Note that there's another minor bug when `diff-buffer-type` isn't equal
> to 'git: `diff--font-lock-prettify` should be a no-op since the regexp
> written there match only Git generated diffs, confirmed by the FIXME
> string "This has only been tested with Git's diff output." written in
> the implementation).

Here's the corresponding patch: