Re: [PATCH v2] Do not show "diff --git" metainfo with --no-prefix

From: Junio C Hamano <gitster@pobox.com>
Date: Jan 17, 2008, 02:28 UTC
Message-ID: <7vzlv5kwxy.fsf@gitster.siamese.dyndns.org>
In-Reply-To: <alpine.LSU.1.00.0801170151040.17650@racer.site>

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

Show 11 quoted lines

>> No, what you are talking about is a need of negative prefix, which you 
>> did not implement in that no/src/dst-prefix patch.
>
> I'm probably missing something, but wouldn't a "diff --git gitk-git/gitk 
> gitk-git/gitk" instead of "diff --git a/gitk-git/gitk b/gitk-git/gitk" in 
> mbox format be directly grokkable by git-am?
>
>> Using --no-prefix is a _hack_ that may happen to work only when
>> the subtree-merged project is one level down.
>
> Yep.  But my point was more to show that it is still a valid git diff.

My point was that the validness you mentined above is a happenstance, and not a result of a good design.

After I move gitk-git one level down to modules/gitk but before making it as a submodule, the output with --no-prefix will say "diff --git modules/gitk/gitk modules/gitk/gitk", and that will not be a suitable diff for Paul to apply to his tree.

I think he needs "-p2", but then he can already do that to diffs produced without using your --no-prefix that talks about "diff --git a/gitk-git/gitk b/gitk-git/gitk". IOW, --no-prefix is not a solution to anything.

And that is why I keep calling your "--no-prefix happens to work if you are only talking about a project that is subtree-merged one level down" argument a _hack_.

If we were to do this properly in "git diff", we would:

 - introduce a separate --strip-paths=1 (or whatever number of
   levels of leading prefix);

 - not use --{src,dst,no}-prefix

and you would do:

	$ git diff --strip-paths=1 gitk-git

in the current tree, which would first strip one path component and then do the usual opt->a_prefix/b_prefix thing to show:

	diff --git a/gitk b/gitk

Similarly you would run:

        $ git diff --strip-paths=2 modules/gitk

after I move gitk-git down one level.

An alternative would be to use the jc/diff-relative topic currently parked in 'offcuts' branch, and run:

	$ cd gitk-git && git diff .

or

	$ cd modules/gitk && git diff .

which would give diffs in relative paths.