Re: [RFC PATCH] Re: Empty directories...

From: Junio C Hamano <gitster@pobox.com>
Date: Jul 19, 2007, 05:28 UTC
Message-ID: <7vbqe93qtv.fsf@assigned-by-dhcp.cox.net>
In-Reply-To: <alpine.LFD.0.999.0707181710271.27353@woody.linux-foundation.org>

Linus Torvalds <torvalds@linux-foundation.org> writes:

Show 42 quoted lines

> On Thu, 19 Jul 2007, David Kastrup wrote:
>> 
>> Well, kudos.  Together with the analysis from Junio, this seems like a
>> good start.  Would you have any recommendations about what stuff one
>> should really read in order to get up to scratch about git internals?
>
> Well, you do need to understand the index. That's where all the new 
> subtlety happens.
>
> The data structures themselves are trivial, and we've supported empty 
> trees (at the top level) from the beginning, so that part is not anything 
> new.
>
> However, now having a new entry type in the index (S_IFDIR) means that 
> anything that interacts with the index needs to think twice. But a lot of 
> that is just testing what happens, and so the first thing to do is to have 
> a test-suite.
>
> There's also the question about how to show an empty tree in a diff. We've 
> never had that: the only time we had empty trees was when we compared a 
> totally empty "root" tree against another tree, and then it was obvious. 
> But what if the empty tree is a subdirectory of another tree - how do you 
> express that in a diff? Do you care? Right now, since we always recurse 
> into the tree (and then not find anything), empty trees will simply not 
> show up _at_all_ in any diffs.
>
> And what about usability issues elsewhere? With my patch, doing something 
> like a
>
> 	git add directory/
>
> still won't do anything, because the behaviour of "git add" has always 
> been to recurse into directories. So to add a new empty directory, you'd 
> have to do
>
> 	git update-index --add directory
>
> and that's not exactly user-friendly.
>
> So do you add a "-n" flag to "git add" to tell it to not recurse? Or do 
> you always recurse, but then if you notice that the end result is empty, 
> you add it as a directory?

Another issue I thought about was what you would do in the step 3 in the following:

 1. David says "mkdir D; git add D"; you add S_IFDIR entry in
    the index at D;

 2. David says "date >D/F; git add D/F"; presumably you drop D
    from the index (to keep the index more backward compatible)
    and add S_IFREG entry at D/F.

 3. David says "git rm D/F".

Have we stopped keeping track of the "empty directory" at this point?