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

Linus Torvalds [off-list ref] writes:

On Thu, 19 Jul 2007, David Kastrup wrote:

quoted

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?