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
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.