Eric Sunshine [off-list ref] writes:

Peff felt that adding `git config --show-hostname-for-includes` was
probably overkill, but I'd argue that it is necessary to enable users
to deterministically figure out the value to use in their
configuration rather than having to grope around in the dark via
guesswork and trial-and-error to figure out exactly what works.

And the option name doesn't necessarily have to be so verbose; a
shorter name, such as `git config --show-hostname` may be good enough.
Implementing this option would also obviate the need to implement
`test-tool xgethostname` (though, I agree with Junio that `test-tool
gethostname` would have been a better, less implementation-revealing
name).

Yeah, I like that show-hostname thing (which I do not know if "config"
is a good home for, though).