When I updated Xcode (from 6.0 GM to 6.0.1) this morning, my Cocoapods project stopped building with the following complaint:
File '/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator8.0.sdk/usr/include/sysexits.h' has been modified since the precompiled header '/Users/michael/Library/Developer/Xcode/DerivedData/Example_App-fsojmrhygegcdzguhnrtvayaxomy/Build/Intermediates/PrecompiledHeaders/Pods-Example App-FLKAutoLayout-prefix-bwkzwquwvmqedfeasqvdcsmlzrtu/Pods-Example App-FLKAutoLayout-prefix.pch.pch' was built
Exciting stuff! I tried cleaning the project, both the nice way and the mean way (i.e.,
Clean Build Folder...), but that didn't solve the issue. The solution (which should have been obvious if I'd read the error message a bit closer instead of going straight to Google) was to delete
DerivedData, which of course is always the answer. The problem was caused by Xcode updating the iOS frameworks but the
pch files being linked against the old frameworks. Not sure why Xcode didn't check that and clear
DerivedData for me, but there you go.
The moral of the story here is to read the error messages Xcode provides closely (and to always delete
DerivedData is simply deleting the folder
~/Library/Developer/Xcode/DerivedData, or using the excellent plugin DerivedData Exterminator.