This local transform adds a logging ability to your program using Log4j logging. Every method call on a unbound variable named log will be mapped to a call to the logger. For this a log field will be inserted in the class. If the field already exists the usage of this transform will cause a compilation error. The method name will be used to determine what to call on the logger.

log.name(exp)

is mapped to

if (log.isNameEnabled() {
   log.name(exp)
}

Here name is a place holder for info, debug, warning, error, etc. If the expression exp is a constant or only a variable access the method call will not be transformed. But this will still cause a call on the injected logger.