Xcode crashes when closing an Assistant Editor that contains different file types

[nathanhosselton]

Message from crash report:

Sending _segmentStateDidChange: to <IDEEditorModeToolbarViewController: 0x7faf4ee4d990> from <DVTSegmentedControl: 0x7faf4cc1f210>
ProductBuildVersion: 7A220
UNCAUGHT EXCEPTION (NSInternalInconsistencyException): -[NSClipView(0x7faf4ba36040) lockFocus] failed with window=0x7faf50106da0, windowNumber=46937, [self isHiddenOrHasHiddenAncestor]=0
UserInfo: (null)
Hints: 
  0: Sending _segmentStateDidChange: to <IDEEditorModeToolbarViewController: 0x7faf4ee4d990> from <DVTSegmentedControl: 0x7faf4cc1f210>

It's difficult to discern from the report the exact failure reason. Backtrace only indicates that MT kicks off a theme change which the IDE acts on eventually leading to the lockFocus call on the NSClipView where the exception is raised.

Closing the Assistant Editor when the files are of the same type, even when closing it will result in a theme change (which is possible because theme changes while the Assistant Editor is active are currently ignored due to crashes that otherwise result), does not result in a crash. Without knowing the root of this issue, the only obvious workaround is an additional check for when the editor is changing from Assistant to Standard. However, this may prevent a theme update, if relevant, when closing the Assistant Editor, which would be undesirable behavior. Further, I currently have no insertion point for the control's state changing, and I don't believe checking the control itself will produce the required information.

Research is required. No ERD.