The command line generation in WDLGen was less than perfect, so with OpenWDL removing the string interpolator options (OpenWDL:366), it was time for a refresh.
The existing functionality was updated, but preserved through the (CommandArgument | CommandInput).from_fields method (which does this construction for you.
For WDL v1.0 support, please pin illusional.wdlgen <0.3.0, or raise an issue for more support.