I recently came across this problem. I soon realized that the cause had been my own doing. I had previously disabled XCode indexing (which used to take forever & eat up my RAM), using the below code in a terminal window:
defaults write com.apple.dt.XCode IDEIndexDisable 1
To revert XCode to its default state, i used the following line in a terminal window:
defaults write com.apple.dt.XCode IDEIndexDisable 0
Voila! All's well again..
