Re: [RFC/PATCH] WIP: add deprecation & experimental process/interface

[Jeff King <peff@peff.net>]

On Mon, May 29, 2017 at 01:20:02PM +0200, Ævar Arnfjörð Bjarmason wrote:

> >>  * Add a new config variable `core.version`. E.g. `core.version =
> >>    2.14.0` With this the user can specify that they'd like
> >>    new/experimental features introduced in that version (and below),
> >>    as well as immediately getting new deprecations added in that
> >>    version as errors.
> >
> > We have extensions.* for this purpose (or close to this purpose). I
> 
> From reading repository-version.txt it seems unrelated to what I'd
> like to do. I.e. there you'd like to introduce a hard breakage and
> it's already documented that if you encounter some extensions.* keys
> you don't understand you *must not* proceed.
> 
> Whereas for this you'd like to e.g. turn on some experimental feature
> in 2.16, but if you're running a 2.14 git you'd like it to just ignore
> that config key it doesn't know about instead of git breaking.

Right. repostoryformatversion (and extensions) is about the on-disk
format of a repo. If I understand correctly, this is about the user
specifying their preferred behaviors. Which is totally orthogonal.

The former must be set in the repo-level .git/config, and would
generally be set by Git itself when it writes a repo using that feature
(e.g., upcoming ref backends).  But this new thing would likely be set
in the ~/.gitconfig explicitly by the user, when they want to change the
behavior profile.

For that reason, I'd suggest using a name that is a little different
from "core.version", since it's easily missed up with
"core.repositoryformatversion". But that's a minor detail.

-Peff