Supporting git-send-email/hg email in VC

[Antoine Kalmbach]

Would it make sense for Emacs' VC to support emailing patches from
within Emacs? It kind of doesn't make sense that I can do mostly
everything in VC... but I have to jump to the command line (shell) to
use git-send-email.

I was thinking there could be a command called 'vc-mail-commit' which
would in vc-dir-mode or vc-log-mode do the right thing and call git
format-patch and then compose a mail with the contents of the patch (or
the patch attached, depending on customization).

The right thing would be in vc-dir-mode to prompt for a ref (branch, -1,
HEAD^, etc), in vc-log-mode it would be to compose a set of patches from
the marked commit(s), or prompt like in vc-dir-mode for a ref to send a
patch from a user-specified ref.

Does such a feature make sense? I know sites like git-send-email.io[1]
say things like:

> Warning! Some people think that they can get away with sending patches
> through some means other than git send-email, but you can't. Your
> patches will be broken and a nuisance to the maintainers whose inbox
> they land in. Follow the golden rule: just use git send-email.

But I find that if and only if you use git-format-patch, the end result
is pretty much the same. To that end, I think if Emacs managed to
integrate with the different DVCS' email-based workflows, it would be
a great usability improvement.

If people think this would be a useful feature, I can open a bug report
to track this and start working on it. The proposed reference
implementation for Git would be to (1) ask the user for a ref (2) call
git format-patch with that (3) compose a new message in Emacs, and set
the body of the message to be the output of git-format-patch (OR attach
the file) and (4) let the MUA take it from there.

Alternatively, it would be possible to use a combination of with-editor
+ git-send-email, but only if we should need ot abide by the "rule",
because to me there aren't many nuances beyond using the format
specified by git-format-patch with your own MUA vs. using
git-send-email. Or do I not know enough about the latter to not see the
missing pieces?

[1] https://git-send-email.io/#step-3

-- 
Antoine Kalmbach