Re: Plugin mechanism(s) for Git?

From: Lars Schneider <larsxschneider@gmail.com>
Date: Jul 15, 2016, 07:37 UTC
Message-ID: <2C31984D-310C-4E8C-927B-6D98B7D7570B@gmail.com>
In-Reply-To: <CAP8UFD1BnnRqsv8zrcDDby=KqQ3UCDVdHWTycfDNTeyfLArn5g@mail.gmail.com>

Show 27 quoted lines

> On 15 Jul 2016, at 08:46, Christian Couder <christian.couder@gmail.com> wrote:
> 
> [...]
> 
> The current topics/work I can think of are:
> 
> - the ref backend work by Michael based on Ronnie Sahlberg's and others' work,
> - the smudge/clean filters work by Joey and Lars,
> - the watchman/index helper work by David, Duy and Ben,
> - the external ODB work by Peff and myself.
> 
> They all have a need to talk to potentially different
> backends/external processes and this need is potentially not well
> satisfied by the usual mechanism that Git has traditionally used which
> is to have one or a few commands configured and to just launch the
> command(s) for each file or object, like what "git difftool" and "git
> mergetool" do.
> 
> [...]
> 
> If people think that evolution is better than intelligent design, and
> want each current topic/work to just implement what is best for it,
> then that's ok for me. If on the other hand standardizing on some ways
> to interact with external processes could be helpful to avoid
> duplicating mechanisms/code in slightly different and incompatible
> ways, then I would be happy to discuss it in a thread that is not
> specific to one of the current work.

Thanks for this great summary of the problem, Christian!

I think a generic plugin mechanism would be great but how would we do it?

We could dynamically load libraries but this would force us to freeze the ABI as mentioned by Duy: http://article.gmane.org/gmane.comp.version-control.git/298463

Unix sockets are not really portable as mentioned by Dscho: http://article.gmane.org/gmane.comp.version-control.git/298432

So far the pipe communication used by the clean/smudge filter seems to be a good option. Maybe we could "standardize" some kind of protocol over pipes?

I also like your ODB work and I think it is the right thing to do in the long run. However, I only have a couple of hours a week to work on this and improving an existing solution seemed easier to me (ODB would require bigger changes in Git and Git-LFS for instance).

Thanks, Lars