Re: [PATCH 5/7] tmp-objdir: new API for creating and removing primary object dirs

Jeff King [off-list ref] writes:

  - is it possible for the merge code to ever write an object? I kind of
    wonder if we'd ever do any cache-able transformations as part of a
    content-level merge. I don't think we do now, though.

How is virtual merge base, result of an inner merge that recursively
merging two merge bases, fed to an outer merge as the ancestor?
Isn't it written as a tree object by the inner merge as a tree with
full of blob objects, so the outer merge does not have to treat a
merge base tree that is virtual any specially from a sole merge
base?