I think we need to make these cases more concrete to have a meaningful discussion. Between Doug and Gregory, I'm understanding two different use cases:

1. Existing, legacy code, built again some historical version of Hackage, without information on the exact versions of all deep dependencies.

2. Someone starting a new project who wants to use an older version of a package on Hackage.

If I've missed a use case, please describe it.

For (1), let's start with the time machine game: *if* everyone had been using the PVP, then theoretically this wouldn't have happened. And *if* the developers had followed proper practice and documented their complete build environment, then PVP compliance would be irrelevant. So if we could go back in time and twist people's arms, no problems would exist. Hurray, we've established that 20/20 hindsight is very nice :).

But what can be done today? Actually, I think the solution is a very simple tool, and I'll be happy to write it if people want: cabal-timemachine. It takes a timestamp, and then deletes all cabal files from our 00-index.tar file that represent packages uploaded after that date. Assuming you know the last date of a successful build, it should be trivial to get a build going again. And if you *don't* know the date, you can bisect until you get a working build. (For that matter, the tool could even *include* a bisecter in it.) Can anyone picture a scenario where this wouldn't solve the problem even better than PVP compliance?

I still maintain that new codebases should be creating freeze files (or whatever we want to call them), and we need a community supported tool for it. After speaking with various Haskell-based companies, I'm fairly certain just about everyone's reinvented their own proprietary version of such a tool.

For (2), talking about older versions of a package is not relevant. I actively maintain a number of my older package releases, as I'm sure others do as well. The issue isn't about *age* of a package, but about *maintenance* of a package. And we simply shouldn't be encouraging users to start off with an unmaintained version of a package. This is a completely separate discussion from the legacy code base, where- despite the valid security and bug concerns Vincent raised- it's likely not worth updating to the latest and greatest.

All of that said, I still think the only real solution is getting end users off of Hackage. We need an intermediate, stabilizing layer. That's why I started Stackage, and I believe that it's the only solution that will ultimately make library authors and end-users happy. Everything we're discussing now is window dressing.

My offer of cabal-timemachine was serious: I'll be happy to start that project, and I *do* think it will solve many people's issues. I'd just like it if it was released concurrently with cabal-freeze, so that once you figure out the right set of packages, you can freeze them in place and never run into these issues again.

Michael