After installing Xcode 9 beta, Xcode 8 gives me an error when compiling a project:
Cannot find cdtool at '/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/Library/Xcode/Agents/cdtool': Cannot find a simulator runtime for platform
<DVTPlatform:0x7fd67af0a930:'com.apple.platform.iphonesimulator':<DVTFilePath:0x7fd67af0a7c0:'/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform'>>
.
I suspect Xcode 9 modified some shared state with Xcode 8 (set a path, overwrote a file, etc.). But I've tried deleting and both Xcodes to no avail.
The project uses Core Data and it's clearly failing when trying to compile the xcdatamodel.
I can still compile and run under Xcode 9.