Erik Faye-Lund [off-list ref] writes:
So, basically, ls-files and ls-tree seems to think
find_unique_abbrev() does not correctly (for this purpose) handle
abbrev=0. However, show-ref does seem to assume so.
I think this is merely historical; the former two were written way back
before corner case behaviour, namely length=0 case, was cast in stone, and
hence they call f-u-a unnecessarily defefnsively.
.