# Bumping Hackage and Stackage snapshots

`haskell.nix` relies on some generated data providing information about packages in Hackage and Stackage snapshots.
These are kept in [`hackage.nix`](https://github.com/input-output-hk/hackage.nix) and [`stackage.nix`](https://github.com/input-output-hk/stackage.nix) respectively.
If your project depends on a Hackage package, then the `hackage.nix` revision used must be new enough to contain that, and likewise for Stackage snaphots and `stackage.nix`.

## Updating and pinning `hackage.nix` and `stackage.nix`

`haskell.nix` pins particular revisions of these repositories internally, both for our own usage in testing, and so that users have a sensible default when getting started.
These revisions are updated nightly, so you can get newer revisions of `hackage.nix` and `stackage.nix` by updating your revision of `haskell.nix` itself.

However, this exposes you to changes in `haskell.nix` which you may not want, such as changes that force compiler rebuilds, or the occasional bug.
Instead, you can pin `hackage.nix` and `stackage.nix` independently. For example:

```nix
{{#include hackage-stackage/default.nix}}
```

This way you can change the revisions of `hackage.nix` and `stackage.nix`
without changing `haskell.nix`.

However, bear in mind that Stackage refers to Hackage, so your Stackage pin
should never be newer than your Hackage pin.