Re: Avery Pennarun's git-subtree?

Avery Pennarun [off-list ref] writes:

...  There is one problem I don't know how to
solve with this idea, though: what happens when commit A adds a
submodule in modules/mod1, commit B removes it, and then commit C
re-adds the same submodules in modules/mod1-again?  Will it reuse the
same submodule .git directory or a new one?  Share objects or not?
Share branch names or not?  Share .git/config or not?

Unless you have some kind of "unique id" scheme for submodules, this
gets impossible to handle correctly.  And the git objects themselves
(trees that link to commits) have nowhere to put such things.

I vaguely recall that we already had discussed and more or less resolved
it at the design level at some point.  Looking for "three-level thing" in
the gmane archive might be beneficial, although all I recall these three
words as search keywords and do not have a detailed recollection of actual
discussion ;-)