For the haskell-build-system I want to offer two outputs by default: "out" and "static". However, the build system has no way to override the default as (@ (guix packages) package->bag) passes the package’s “outputs” value to make-bag.
When the package doesn’t define a value for “outputs”, the default '("out") is used. I suggest removing the default value from the <package> record, so that the build system defaults have a chance. -- Ricardo