Re: Pushing and pulling the result of `git replace` and objects/info/alternates

From: Christian Couder <christian.couder@gmail.com>
Date: May 25, 2015, 10:28 UTC
Message-ID: <CAP8UFD20u1OG88bvDAW4vsh=yPihp3TMjc95wDuD=nnr8esBgw@mail.gmail.com>
In-Reply-To: <5562F01D.8000601@gmail.com>

On Mon, May 25, 2015 at 11:49 AM, Stephen Kelly <steveire@gmail.com> wrote:

Show 19 quoted lines

> On 05/24/2015 07:28 AM, Christian Couder wrote:
>> Hi,
>>
>> On Fri, May 22, 2015 at 4:38 PM, Stephen Kelly <steveire@gmail.com> wrote:
>>> I have tried out using `git replace --graft` and
>>> .git/objects/info/alternates to 'refer to' the history in the origin
>>> repo instead of 'duplicating' it. This is similar to how Qt5 repos
>>> refer to Qt 4 history in a different repo.
>>>
>>> Question 1) Is this a reasonable thing to do for this scenario?
>> I think it should work without too much work, but see the answer to
>> the next question.
>
> Ok, thanks. The concern is that there is plenty of documentation for
> git-filter-branch, but no documentation or porcelain for info/alternates
> and little out on the internet about it or git replace and using them
> together.
>
> However, it seems to be a reasonable thing to do.

Yeah.

By the way it looks like I was wrong in my answer to your second question.

You might want to clone using the --reference option to automatically set up .git/objects/info/alternates properly.

(There is an ongoing related thread on the list:

http://thread.gmane.org/gmane.comp.version-control.git/269537)

You might also be able to clone using an option like "--config remote.origin.fetch = 'refs/replace/*:refs/replace/*'" to fetch the replace ref when cloning.

So it looks like you might just need to clone with a few more options than usual.

I haven't tested it so please tell me if it works :-)

Show 17 quoted lines

>>> echo "../../calculator/objects" >
>>> ../.git/modules/compute/objects/info/alternates
>>> git replace --graft HEAD $extraction_sha
>> Maybe use the following instead of the above line:
>>
>> git fetch 'refs/replace/*:refs/replace/*'
>
> Thanks.
>
>>> # And now we see the history from the calculator repo. Great. But, it
>>> required user action after the clone.
>> Yeah, but if the 2 above commands are in a script maybe it's
>> reasonable to ask the user to launch the script once after cloning.
>
> Would it be possible to do this in a hook in the 'integration repo'
> which contains both submodules in the example I posted? Like a fetch
> hook or something?

It is possible to do whatever you want in a hook, but the question is why would you do it in a hook as it looks like it needs to be done only once?

Or maybe I am missing something?

Best, Christian.