Fix .setShortcut() crashing when called from a `NSBackgroundActivit…

…yScheduler` task (#9)

Sources/KeyboardShortcuts/NSMenuItem++.swift

@@ -56,7 +56,14 @@ extension NSMenuItem {
 			keyEquivalentModifierMask = shortcut.modifiers
 		}
 
-		set()
+		// `TISCopyCurrentASCIICapableKeyboardLayoutInputSource` works on a background thread, but crashes when used in a `NSBackgroundActivityScheduler` task, so we ensure it's not run in that queue.
+		if DispatchQueue.isCurrentQueueNSBackgroundActivitySchedulerQueue {
+			DispatchQueue.main.async {
+				set()
+			}
+		} else {
+			set()
+		}
 
 		AssociatedKeys.observer[self] = NotificationCenter.default.addObserver(forName: .shortcutByNameDidChange, object: nil, queue: nil) { notification in
 			guard

Sources/KeyboardShortcuts/Shortcut.swift

@@ -170,6 +170,9 @@ private var keyToKeyEquivalentString: [KeyboardShortcuts.Key: String] = [
 
 extension KeyboardShortcuts.Shortcut {
 	fileprivate func keyToCharacter() -> String? {
+		// `TISCopyCurrentASCIICapableKeyboardLayoutInputSource` works on a background thread, but crashes when used in a `NSBackgroundActivityScheduler` task, so we guard against that. It only crashes when running from Xcode, not in release builds, but it's probably safest to not call it from a `NSBackgroundActivityScheduler` no matter what.
+		assert(!DispatchQueue.isCurrentQueueNSBackgroundActivitySchedulerQueue, "This method cannot be used in a `NSBackgroundActivityScheduler` task")
+
 		// Some characters cannot be automatically translated.
 		if
 			let key = key,
@@ -178,14 +181,19 @@ extension KeyboardShortcuts.Shortcut {
 			return character
 		}
 
-		let source = TISCopyCurrentASCIICapableKeyboardLayoutInputSource().takeUnretainedValue()
-		let layoutData = TISGetInputSourceProperty(source, kTISPropertyUnicodeKeyLayoutData)
-		let dataRef = unsafeBitCast(layoutData, to: CFData.self)
+		guard
+			let source = TISCopyCurrentASCIICapableKeyboardLayoutInputSource()?.takeRetainedValue(),
+			let layoutDataPointer = TISGetInputSourceProperty(source, kTISPropertyUnicodeKeyLayoutData)
+		else {
+			return nil
+		}
+
+		let dataRef = unsafeBitCast(layoutDataPointer, to: CFData.self)
 		let keyLayout = unsafeBitCast(CFDataGetBytePtr(dataRef), to: UnsafePointer<CoreServices.UCKeyboardLayout>.self)
 		var deadKeyState: UInt32 = 0
-		let maxCharacters = 256
+		let maxLength = 4
 		var length = 0
-		var characters = [UniChar](repeating: 0, count: maxCharacters)
+		var characters = [UniChar](repeating: 0, count: maxLength)
 
 		let error = CoreServices.UCKeyTranslate(
 			keyLayout,
@@ -195,7 +203,7 @@ extension KeyboardShortcuts.Shortcut {
 			UInt32(LMGetKbdType()),
 			OptionBits(CoreServices.kUCKeyTranslateNoDeadKeysBit),
 			&deadKeyState,
-			maxCharacters,
+			maxLength,
 			&length,
 			&characters
 		)

Sources/KeyboardShortcuts/util.swift

@@ -328,3 +328,21 @@ final class ObjectAssociation<T: Any> {
 		}
 	}
 }
+
+
+extension DispatchQueue {
+	/**
+	Label of the current dispatch queue.
+
+	- Important: Only meant for debugging purposes.
+
+	```
+	DispatchQueue.currentQueueLabel
+	//=> "com.apple.main-thread"
+	```
+	*/
+	static var currentQueueLabel: String { String(cString: __dispatch_queue_get_label(nil)) }
+
+	/// Whether the current queue is a `NSBackgroundActivityScheduler` task.
+	static var isCurrentQueueNSBackgroundActivitySchedulerQueue: Bool { currentQueueLabel.hasPrefix("com.apple.xpc.activity.") }
+}