In regards to Xcode's knack of filling up the hard drive, how do I prevent that from happening?
How much free space on your drive right now? Click on the Apple logo, top left in the menu bar, then 'About This Mac', then the 'Storage' tab - how many GB does it say as 'available' on your main drive? What is the total size of that drive?
There were reports of Xcode going nuts and writing temp files that weren't cleared up.
This isn't the same as a routine build up of 'Derived Data' that is normal, and primarily an issue for users with smaller drives who need to budget drive space.
I'd keep an eye on your free space and how long it takes for it to drop significantly.
- If free space is consumed slowly, I'd make an effort to delete derived data as part of your routine housekeeping. See this SO thread: https://stackoverflow.com/questions/46468220/how-to-delete-derived-data-in-xcode-9
- If it drops quickly, that's another issue we can try to tackle when it happens.