Re: [PATCH 2/3] merge-recursive: make empty tree a known object

[Linus Torvalds <torvalds@osdl.org>]

On Sun, 10 Dec 2006, Johannes Schindelin wrote:
> 
> To use it in diff_tree_sha1(), a tree has to be hashed in the
> global object collection. This actually moves the empty tree (if
> it is needed) into the global object hash.

I think you should do this more generically.

If we create this kind of "default fake object" that we know about whether 
the object _really_ exists or not (and I agree it makes sense for the 
empty tree), we should probably use it for "diff_root_tree_sha1()" too, 
rather than the special case we have now.

In other words, right now we have that very special 
"diff_root_tree_sha1()" function, but if you create a generic fake "empty 
tree" SHA1 that git knows about implicitly, we could entirely replace it 
with just using

	diff_tree_sha1(EMPTY_TREE_SHA1, tree, base, opt);

instead, and get rid of that special case code (which is efficient, but we 
don't really _need_ the efficiency).

So you could make "read_sha1_file()" just have a special case for known 
objects at the end. If the pack entry fails, the loose file case fails, 
then rather than returning NULL at the end, you could have a list of known 
fixed objects..

Hmm?