Or maybe provide a flag to switch the default?

I get this error when running the hello world example from docs on nixos:

cromwell.core.CromwellFatalException: java.io.IOException: Cannot run program "/bin/bash": error=2, No such file or directory

Is it just to change this line?

I could possibly just make my own version building from source then ..

It is due to the way nixos is built. A similar case is referenced here :

RcppCore/RcppArmadillo#15