# How to upgrade packages in this repo

## Stackage

The daml repository uses a custom stack snapshot defined in
`stack-snapshot.yaml`. Modify the `resolver` entry in that file to update the
base Stackage snapshot. Update the package overrides defined in that file as
appropriate.

A few Stackage packages require custom patches or custom build rules. These are
defined in the `WORKSPACE` file and referenced in the `vendored_packages`
attribute to `stack_snapshot` in the same file.

After changing any of this entries you need to execute the following command to
update the lock-file:

```
bazel run @stackage-unpinned//:pin
```


## Nixpkgs

To update the nixpkgs revision, find a commit in nixkgs-unstable from
https://github.com/NixOS/nixpkgs/commits/nixpkgs-unstable and
use it in the `rev` field in `nix/nixpkgs/default.src.json`.  Set the
`sha256` to a dummy hash, e.g., 64 zeros and run `nix-build -A tools
-A cached nix` and nix will tell you the correct hash.

After upgrading the revision, the easiest solution is usually to open
a PR and see what fails on CI (running the builds locally can take
quite some time). The most common reason for failures is usually that
we have overriden a specific package with certain patches that no
longer work. In that case, a good first step is to check if these
patches are still necessary and if not try to switch to the unpatched
package from nixpkgs.