[MERGE] deprecated EmptyTree

[Martin Pool]

On 21 Jul 2006, Robert Collins <robertc at robertcollins.net> wrote:
> > > Or does their ROOT_ID id count as
> > > a root file-id ?
> > 
> > Exactly.  TREE_ROOT counts as a root file-id.
> 
> What do you think of having the empty tree have a root with a file-id of
> ROOT_ID ? I think it is a desirable property that an empty tree be able
> to match precisely a tree committed with no files and no ancestors.
> 
> I realise this is different to what you have done - so I'd like to know
> what things it would impact negatively.

I'm not sure what Aaron did or would have done, but it sounds plausible.
If we use a different root id it needs to be assigned somehow in the
space between the empty tree and the first commit.  (I say in that space
because it can happen at commit, though I think we said it would happen
when the working tree is built.)  But representing that as addition of a
new id to the root (rather than insertion of a new root directory)
seems OK.

-- 
Martin