InstallableValue has children InstallableFlake and InstallableAttrPath, but InstallableFlake was overriding toDerivations, and usage was changed so that InstallableFlake didn't need cmd. So these changes were made:
InstallableValue::toDerivations() -> InstalllableAttrPath::toDerivations()
InstallableValue::cmd -> InstallableAttrPath::cmd
InstallableValue uses state instead of cmd
toBuildables() and toDerivations() were made abstract
Matthew Kenigsberg
9f4cfbb2e7