Re: [PATCH] Add 'git fast-export', the sister of 'git fast-import'

From: Junio C Hamano <gitster@pobox.com>
Date: Nov 26, 2007, 17:55 UTC
Message-ID: <7vsl2sgadf.fsf@gitster.siamese.dyndns.org>
In-Reply-To: <Pine.LNX.4.64.0711261236280.27959@racer.site>

Johannes Schindelin <Johannes.Schindelin@gmx.de> writes:

Show 12 quoted lines

> On Sun, 25 Nov 2007, Junio C Hamano wrote:
>
>> I am not sure if abort should be the default.
>
> I tried to be conservative.
>
>> If a straight dump-restore is made without rewriting, the result will be 
>> identical to the original, right?
>
> Yep.
> ...
> I agree that for most serious operations sed is not good enough.

My comment was more about the perception from a new user (not a "new git user", but a "new fast-export and fast-import user").

When you see a command pair foo-export and foo-import, and it is advertised that you can pipe them together, a new user would first try a straight dump-restore, and would see the warning even though he did not do any editing on the stream.

	Huh?  Why does a tag signature become invalid because of merely
	exporting and then importing?  What is this warning about?

You would explain "yeah in your trial run you did not edit but the command pair is to allow you editing the contents in between, and if you do that, the object names might change.".

If the default were "straight copy", then the user will not get an invalid signature on his trial run, but will get an invalid signature when he rewrites the object stream. You would get a message on the list like this:

	Hello, I tried fast-export piped to fast-import so that I can
	rewrite my repository, but I am getting invalid signature on
	signed tags.  It does not seem to happen if I do not edit but
	just use the fast-export output without modification.  What am I
	doing wrong?

And that is the time the explanation first becomes useful. IOW, you are warning at the wrong place. "It may or may not corrupt the signature, I do not know. Because it depends on what you are going to do with my output, I cannot know. I am warning you anyway to cover my backside".

I am wondering if fast-import input syntax can be extended to allow checking inconsistencies. A command to import a tag could take an additional object name and tell it to warn if the name of the tagged object (the one sent with "from:%d\n" part) is different from that object name. At that point, you know the object was rewritten and the signature is invalid, and the choice of warning, stripping or aborting becomes a useful thing to have.