Re: Round-tripping fast-export/import changes commit hashes

From: Junio C Hamano <gitster@pobox.com>
Date: Mar 1, 2021, 17:34 UTC
Message-ID: <xmqqblc2srq0.fsf@gitster.c.googlers.com>
In-Reply-To: <CAPkN8xLE68d5Ngpy+LOQ8SALNgfB-+q4F3mFK-QBD=+EOKZSVg@mail.gmail.com>

anatoly techtonik <techtonik@gmail.com> writes:

> Is fast-export/import the only way to filter information in `git`? Maybe there
> is a slow json-export/import tool that gives a complete representation of all
> events in a repository? Or API that can be used to serialize and import that
> stream?

I do not think representation is a problem.

It is just that the output stream of fast-export is designed to be "filtered" and the expected use case is to modify the stream somehow before feeding it to fast-import. And because every object name and commit & tag signature depends on everything that they can reach, even a single bit change in an earlier part of the history will invalidate any and all signatures on objects that can reach it. So instead of originally-signed objects whose signatures are now invalid, "fast-export | fast-import" pipeline would give you originally-signed objects whose signatures are stripped.

Admittedly, there is a narrow use case where such a signature invalidation is not an issue. If you run fast-export and feed that straight into fast-import without doing any modification to the stream, then you are getting a bit-for-bit identical copy.

But "git clone --mirror" is a much better way to do get such a bit-for-bit identical history and objects. And if you want to do so with sneakernet, you can create a bundle file, sneakernet it to your destination, and then clone from the bundle.

So...