Open Radar

 
Summary:

I was having a hard time with the error in the attached screenshot. I could build-and-run on a simulator, but if I quit the simulator and build-and-ran again, it would fail. I could fix it only by deleting the app from the simulator. 

On the suggestion of Russ Bishop ( https://twitter.com/xenadu02/status/1068629603684573184 ) I ran an xcrun simctl diagnose (attached). It was a good suggestion, becuase I checked CoreSimulator.log and found the following line:

> Nov 30 20:04:00 Open-Source-by-Detente com.apple.CoreSimulator.simctl[81038] <Warning>: Unable to determine how to handle launch_sim_unregister_endpoint for runtime com.apple.CoreSimulator.SimRuntime.iOS-8-1 (handle=0x7f898046b660)

Looks like it was trying to do something with the 8.1 simulator even though it's not installed, which is why I think it was failing. Xcode was still listing 8.1 as being installed in its settings' Components pane, but I think I had deleted it from the Device Support folder to reclaim disk space. This may have been around when this started, I can't remember.

I eventually tracked down this file and deleted it:

/Library/Developer/CoreSimulator/Profiles/Runtimes/iOS\ 8.1.simruntime

Everything is working now, thanks!

Steps to Reproduce:

- Build and run a project, wait for simulator to launch
- Quit the simulator app
- Build and run again, and get the error

Version/Build:

Xcode Version 10.1 (10B61)