Detecting pushes originating from shallow clones?

Hi folks,

Here at Heroku, we ingest code from users by supplying them with a Git server they can `git push` into. Occasionally, users will attempt to push to us from a shallow clone, which causes numerous problems for us and, often, for our users (incomplete repositories, gaps in history, failed builds, and a host of other problems). We’ve been investigating what we can do to give these users clearer advice on how to fix the problem.

Within the constraints that

* we cannot control which version of Git our users have installed, and
* we run Git v1.9.1, obtained from the Ubuntu 14.04 LTS .deb repositories

what can we do in an update/pre-receive hook to detect that an incoming push originates from a shallow repository and reject it?

Right now, the best strategy we have is to observe whether

    git rev-list OLD NEW

fails, and if it does fail, whether the stderr output includes the phrase "revision walk setup failed”. This feels like a fairly weak fix, so I thought I’d see if anyone here has a better idea.

Thanks,

-o