I had a similar issue, using MacOS Mojave 10.14
Apparently my xcode path was pointing to command line tools instead of the Xcode.app in /Applications.
(was also hinted by the Metal shader compilation warning about reverting to default shaders)
If anyone is getting the same issue, you can try checking your xcode path in Terminal:
xcode-select -p
This should say
/Applications/Xcode.app/Contents/Developer
If not, point this to the right directory by entering this:
sudo xcode-select -s /Applications/Xcode.app/Contents/Developer
This switches the default path of xcode to the one in /Applications.
Hope this helps!