Most of SWIG directives for wrappers are generated automatically with scripts/wrap. E.g. all header files in include/btllib are automatically included without developer intervention. However, some aspects of SWIG need to be manually setup and for that you need to modify either extra_common.i file in this directory (features common to all wrapped languages) or <language>/extra.i for the language you want to setup features for. These and if needed meson.build are the only files you should be modifying in wrappers/, the rest is autogenerated.