Hi,
When I open an existing project (following https://developer.apple.com/tutorials/swiftui/creating-and-combining-views) in Xcode, it crashes immediately with this "(tabController) should not be nil." error:
(tabController) should not be nil.
Process:							 Xcode [11567]
Path:									/Applications/Xcode.app/Contents/MacOS/Xcode
Identifier:						com.apple.dt.Xcode
Version:							 12.3 (17715)
Build Info:						IDEFrameworks-17715000000000000~8 (12C33)
App Item ID:					
App External ID:			
Code Type:						 ARM-64 (Native)
Parent Process:				??? [1]
Responsible:					 Xcode [11567]
User ID:							 501
Date/Time:						 2020-12-19 01:09:44.783 +1100
OS Version:						macOS 11.1 (20C69)
Report Version:				12
Anonymous UUID:				
Sleep/Wake UUID:			
Time Awake Since Boot: 40000 seconds
Time Since Wake:			 310 seconds
System Integrity Protection: enabled
Crashed Thread:				0	Dispatch queue: com.apple.main-thread
Exception Type:				EXC_CRASH (SIGABRT)
Exception Codes:			 0x0000000000000000, 0x0000000000000000
Exception Note:				EXC_CORPSE_NOTIFY
Application Specific Information:
ProductBuildVersion: 12C33
ASSERTION FAILURE in /Library/Caches/com.apple.xbs/Sources/IDEFrameworks/IDEFrameworks-17715/IDEKit/Workspace/IDEWorkspaceDocument.m:3270
Details:	(tabController) should not be nil.
Object:	 <IDEWorkspaceDocument: 0x11d5fdb20>
Method:	 -commitStateToDictionary:
Thread:	 <NSThread: 0x140628ff0>{number = 1, name = main}
Open FDs: 38/7168
Hints:	
Backtrace:
	0	 -[IDEAssertionHandler handleFailureInMethod:object:fileName:lineNumber:assertionSignature:messageFormat:arguments:] (in IDEKit)
	1	 _DVTAssertionHandler (in DVTFoundation)
	2	 _DVTAssertionFailureHandler (in DVTFoundation)
	3	 -[IDEWorkspaceDocument showWindows] (in IDEKit)
	4	 -[DVTStateToken _copyStatefulObjectState] (in DVTFoundation)
	5	 -[DVTStateToken pushStateToRepositoryAndReturnError:] (in DVTFoundation)
	6	 -[DVTStateRepository _updateStateIfNeeded] (in DVTFoundation)
	7	 -[DVTStateRepository collectStateFromRegisteredObjects] (in DVTFoundation)
	8	 -[IDEWorkspaceDocument writeStateData] (in IDEKit)
	9	 __28-[IDEWorkspaceDocument init]_block_invoke (in IDEKit)
10	 -[DVTDelayedInvocation runBlock:] (in DVTFoundation)
11	 __NSFireDelayedPerform (in Foundation)
12	 CFRUNLOOP_IS_CALLING_OUT_TO_A_TIMER_CALLBACK_FUNCTION (in CoreFoundation)
13	 __CFRunLoopDoTimer (in CoreFoundation)
14	 __CFRunLoopDoTimers (in CoreFoundation)
15	 __CFRunLoopRun (in CoreFoundation)
16	 CFRunLoopRunSpecific (in CoreFoundation)
17	 RunCurrentEventLoopInMode (in HIToolbox)
18	 ReceiveNextEventCommon (in HIToolbox)
19	 _BlockUntilNextEventMatchingListInModeWithFilter (in HIToolbox)
20	 _DPSNextEvent (in AppKit)
21	 -[NSApplication(NSEvent) _nextEventMatchingEventMask:untilDate:inMode:dequeue:] (in AppKit)
22	 -[DVTApplication nextEventMatchingMask:untilDate:inMode:dequeue:] (in DVTKit)
23	 -[NSApplication run] (in AppKit)
24	 NSApplicationMain (in AppKit)
25	 start (in libdyld.dylib)
abort() called
Application Specific Signatures:
((tabController)) != nil
Are there any workarounds?
SunsetBoulevard
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Here's a demo: imgur.com/a/88pSV0w.
Xcode 12 has so many intermittent bugs, even in its simpler subsystems and components.
I hope Apple fixes these issues ASAP, but are there any workarounds for the meantime?
Sometimes when I reopen a project the component preview pane fails with the following error message:
NoBuildableEntriesError: active scheme does not build this file Select a scheme that builds a target which contains the current file, or add this file to a target that is built by the current scheme. How can I resolve this and prevent it from happening again?