Open Radar

 
Summary:
If you're interested in debugging swift incremental compilation issues, one nice flag for the compiler you can use is `-driver-show-incremental`. When doing this in Xcode, Xcode occasionally crashes.

Steps to Reproduce:
1. Create a new Swift project
2. Add `-driver-show-incremental` to `OTHER_SWIFT_FLAGS`
3. Compile it a few times, changing things each time

Expected Results:
Xcode happily runs, and has extra log output.


Actual Results:
Xcode crashes with this stacktrace:

2017-02-19 08:43:13.041 xcodebuild[12733:349003]  DVTAssertions: ASSERTION FAILURE in /Library/Caches/com.apple.xbs/Sources/IDELanguageSupport/IDELanguageSupport-11752/XCLanguageSupport/XCSwiftCommandOutputParser.m:230
Details:  (subcommand) should not be nil.
Object:   <XCSwiftCommandOutputParser: 0x7fb03681d380>
Method:   -handleCommandExitedMessage:didSignal:error:
Thread:   <NSThread: 0x7fb036c0ae50>{number = 2, name = (null)}
Hints: None
Backtrace:
  0   -[DVTAssertionHandler handleFailureInMethod:object:fileName:lineNumber:assertionSignature:messageFormat:arguments:] (in DVTFoundation)
  1   _DVTAssertionHandler (in DVTFoundation)
  2   _DVTAssertionFailureHandler (in DVTFoundation)
  3   -[XCSwiftCommandOutputParser handleCommandExitedMessage:didSignal:error:] (in XCLanguageSupport)
  4   -[XCSwiftCommandOutputParser handleMessage:error:] (in XCLanguageSupport)
  5   -[XCSwiftCommandOutputParser writeBytes:length:] (in XCLanguageSupport)
  6   -[XCLineBufferedOutputStream writeBytes:length:] (in DevToolsCore)
  7   -[XCWorkQueueCommandSubprocessInvocation handleOutputBytes:length:] (in DevToolsCore)
  8   -[XCWorkQueueCommandLocalSubprocessInvocation handleOutputFileDescriptorActivity] (in DevToolsCore)
  9   -[Xcode3BuildTask main] (in DevToolsCore)
 10   -[__NSOperationInternal _start:] (in Foundation)
 11   __NSOQSchedule_f (in Foundation)
 12   _dispatch_client_callout (in libdispatch.dylib)
 13   _dispatch_queue_serial_drain (in libdispatch.dylib)
 14   _dispatch_queue_invoke (in libdispatch.dylib)
 15   _dispatch_root_queue_drain (in libdispatch.dylib)
 16   _dispatch_worker_thread3 (in libdispatch.dylib)
 17   _pthread_wqthread (in libsystem_pthread.dylib)
 18   start_wqthread (in libsystem_pthread.dylib)

Version:
Xcode 9.0 beta 1 (9M136h)

Notes:
See https://bugs.swift.org/browse/SR-4001 for more details