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

[Junio C Hamano <gitster@pobox.com>]

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

>> 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.