Re: git subtree error (just how do you expect me to merge 0 trees?)

Drew Crawford [off-list ref] writes:

Ideally it would be better to emit an error-message from a script
higher up the calling chain that would be more descriptive about the
problem (such as suggesting no branch is specified).--

I'm looking at implementing this but I need a bit of help from the git
experts.

git-subtree add accepts either a refspec or a path to a repository and a
refspec.  With one positional option, git-subtree add simply assumes
it's a refspec.  Is there an easy way to check whether a string is a
proper refspec?  Even better would be a way to check if a string is a
path to a git repository.

                         -David