bug#42145: vc-git file order mismatch between vc-dir and vc-diff

[Juri Linkov <juri@linkov.net>]

>> There is an old usability problem in vc-dir.
>> Typing ‘=’ in a vc-dir buffer displays a vc-diff buffer where files are
>> sorted by different order than files are sorted in the vc-dir buffer.
>
> vc-dir has its own presentation logic, it's pretty complex.

The current sorting order in vc-dir is quite good,
so better not to change it.

> 'git diff' has a '-O' argument, which accepts <orderfile>. Maybe it'll
> help, but I kind of doubt that. Ideas welcome.

Maybe it's possible to write a diff-mode function to sort file hunks in
vc-diff output buffer?  Maybe by just giving the right file-beginning regexp
to sort-subr?

> Here's a bigger feature I've wanted to see in VC for a while: commit from
> a diff.
>
> There is a third-party package: https://github.com/caldwell/commit-patch
>
> But it implements some of its logic in Perl, and the message buffer it
> creates is non-standard. I'd really like to see it ported to VC.

Nice idea.

> The idea is, you open a diff, maybe split some of the hunks, kill the ones
> you don't need (diff-mode supports all these operations), and then commit
> the remaining ones, from multiple files, if needed. Seems like a good
> replacement for 'git add -p' for Emacs power users.

But I wonder how it could handle binary files where git-diff output says just
"Binary files differ".