1. Create a new Drools project:

File -> New -> Other -> Drools Project
Choose Name, click Next
Check all options
Choose Drools Runtime, click Finish

2. Open sample.drl file

3. Check code completion on import; m : Message

It doesn't work for me. I checked that this works normally on Linux using the Code Completion shortcut. On Mac when in a Java class, code completion works instantly whenever it can and without any shortcut. When in the drl file, it doesn't seem to work. Maybe it would work with a shortcut, but I don't know which shortcut - in Preferences I only found Word Completion which is something else - it seems that on Mac, code completion always works instantly.