Re: index-pack outside of repository?

Jeff King [off-list ref] writes:

In older versions of git will just blindly write into
".git/objects/pack", even though there's no repository there.

So I think complaining to the user is the right thing to do here. I
started to write a patch to have index-pack notice when it needs a repo
and doesn't have one, but the logic is actually a bit unclear.  Do we
need to complain early _just_ when --stdin is specified, or does that
miss somes cases?  Likewise, are there cases where --stdin can operate
without a repo? I couldn't think of any.

I think there are two and only two major modes; --stdin wants to put
the result in the repository it is working on, while the other mode
takes a filename to deposit the result in, so the latter does not
technically need a repository.

I'm actually wondering if the way it calls die() in 'next' is a pretty
reasonable way for things to work in general. It happens when we lazily
try to ask for the repository directory. So we don't have to replicate
logic to say "are we going to need a repo"; at the moment we need it, we
notice we don't have it and die. The only problem is that it says "BUG"
and not "this operation must be run in a git repository".

Isn't what we currently have is a good way to discover which
codepaths we missed to add a check to issue the latter error?

That strategy _might_ be a problem for some programs, which would want
to notice the issue early before doing work. But it seems like a
reasonable outcome for index-pack. Thoughts?

That is, once we know which codepaths should require a repository, I
think it is reasonable to add a check that is done earlier than the
place where we currently try to see where we have one (which could
be deep in the callchain).  But we are all human and can miss things,
so the BUG() thing is probably fine.  We are cooking it exactly because
we would want to find such corner cases we missed, no?