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

["Ævar Arnfjörð Bjarmason" <avarab@gmail.com>]

On Mon, May 29, 2017 at 12:23 PM, Duy Nguyen <pclouds@gmail.com> wrote:
> On Sat, May 27, 2017 at 6:10 PM, Ævar Arnfjörð Bjarmason
> <avarab@gmail.com> wrote:
>> This is the WIP start of a deprecation & experimental interface to
>> git. The goal is to formalize the workflow around deprecating
>> features, or around introducing new experimental features.
>>
>> This is much more idea than code at the moment, but included is an
>> example showing how :/ might be deprecated[1] (let's not discuss /if/
>> we should do that here, this is just an example).
>>
>> The plan, subject to RFC feedback is to:
>>
>>  * 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.

> think it's more flexible to go with extensions.* instead of a single
> "core.version". extensions.* are non-optional though (if a git binary

I'd like there to be both, and the experimental() function would
define this on the source level, i.e. the call would include a
corresponding version where it was introduced, and a config key to
toggle it individually.

The reason to have both is that you can just upgrade git and say "I'm
not concerned about backcompat here, please give me all the latest
features" without having to exhaustively hunt down the list of things
we're shipping with that version.

> does not understand it, the repo can't be accessed). So it's more
> about fundamental experiments (like sha256 transition). I'm guessing
> we can have a "soft" extensions (warn if not understand, instead of
> die), like what we have in $GIT_DIR/index.

> Deprecation via extension.* though may be unintuitive. But I think
> something along that line (e.g. deprecation.*) might work.