Re: Properties of trees referencing commit objects (mode 160000)?

On Sun, Mar 20, 2016 at 12:18:04AM -0400, Jeff King wrote:

On Sat, Mar 19, 2016 at 03:13:48PM -0700, Josh Triplett wrote:

quoted

I'm building some tools to track commit objects, and I'm thinking of
using submodule-style references to commit objects in tree objects (mode
160000) to do so.  I'm trying to figure out some of the properties of
that.

Can a commit object referenced that way live in the same repository,
rather than some external repository?

Yes, it can be in the same repository, but...

Will git clone/checkout/etc handle it properly in that case, in the
absence of a .gitmodules file?  Or would it only work with custom tools?

quoted

Will git treat such a reference as keeping the commit object (and
everything recursively referenced by it) live and reachable?  If that
commit object is only reachable by the tree, and not by following the
parents of any commit directly referenced from refs/*, will git discard
it as unreachable?

No, we do not follow "gitlinks" like this for reachability. Neither for
pruning, nor for object transfer via push/fetch. So you'd need to have a
separate reference to it (or history containing it).

Argh.  If I have a pile of disconnected commits, is there anything git
*would* follow to see them, other than a pile of refs?

I suppose I could artificially generate a stack of merge commits with
those otherwise disconnect commits as parents, which would let me
reference them all from a single ref.  Still unsatisfying, though.

Also, thanks, "gitlink" was the term I was trying to think of.

(I'd also be tempted to ask whether a patch to teach git to follow
gitlinks for reachability and/or object transfer would be acceptable.)