I had a DNS error on my one server (without knowing this) and the following occured:
--
scorpion% darcs pull --verbose --all http://usrsrc.org/darcs/rupov/

darcs failed:  Not a repository: http://usrsrc.org/darcs/rupov/
--


It was only after a while that i thought to try ping:
--
scorpion% ping usrsrc.org
ping: cannot resolve usrsrc.org: No address associated with name
--

the url provided certainly *is* a repository, even a message that elluded to
some form of network error would be better than: "that is not a repo"

I've just looked into that... and it's tricky.

The guilty party is identifyRepository, in Repository.lhs.  This function checks
for the existence of .../_darcs and .../.git, ignoring errors, and uses whichever
it finds; if it finds neither, it fails with the error message Clive mentioned.

So we must in some way record errors when checking for _darcs and .git, and
report either (or both?) of the errors when both checks failed.  It's going
to be messy.

I'm submitting a patch for that.  The reporting format is horrible, but I guess
that's better than the current state:

$ ./darcs pull http://foo.example.com

darcs failed:  Not a repository: http://foo.example.com (user error (Failed to
download URL http://foo.example.com/_darcs/inventory
libcurl: couldn't resolve host))