This is to improve package location finding at eval time and script execution time.
Deprecates options lock.{repoRoot,lockFileRel} as well as option eval-cache.{repoRoot, cacheFileRel}
Instead the user must now set:
- paths.projectRoot: pointing to the repoRoot
- paths.package: pointing to the package directory
- paths.projectRootFile can be used to define a marker file to find the project root. The default is '.git' but it could be set to 'flake.nix' for example
- lock files are by default put in the same directory as the package definition
