fix: observer leak would throw and crash the app sometimes

alt-tab-macos/api-wrappers/HelperExtensions.swift

@@ -15,11 +15,11 @@ extension Optional {
     // add throw-on-nil method on Optional
     func orThrow() throws -> Wrapped {
         switch self {
-        case .some(let value):
-            return value
-        case .none:
-            Thread.callStackSymbols.forEach { print($0) }
-            throw NSError.make(domain: "Optional", message: "Optional contained nil")
+            case .some(let value):
+                return value
+            case .none:
+                Thread.callStackSymbols.forEach { print($0) }
+                throw NSError.make(domain: "Optional", message: "Optional contained nil")
         }
     }
 }
@@ -64,3 +64,11 @@ extension Collection {
         return flatMap { ($0 as? [Any])?.joined() ?? [$0] }
     }
 }
+
+// removing an objc KVO observer if there is none throws an exception
+extension NSObject {
+    func safeRemoveObserver(_ observer: NSObject, _ key: String) {
+        guard observationInfo != nil else { return }
+        removeObserver(observer, forKeyPath: key)
+    }
+}

alt-tab-macos/logic/Application.swift

@@ -16,6 +16,10 @@ class Application: NSObject {
         }
     }
 
+    func removeObserver() {
+        runningApplication.safeRemoveObserver(self, "isFinishedLaunching")
+    }
+
     private func addAndObserveWindows() {
         axUiElement = AXUIElementCreateApplication(runningApplication.processIdentifier)
         AXObserverCreate(runningApplication.processIdentifier, axObserverApplicationCallback, &axObserver)
@@ -44,7 +48,7 @@ class Application: NSObject {
 
     override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey: Any]?, context: UnsafeMutableRawPointer?) {
         guard let isFinishedLaunching = change![.newKey], isFinishedLaunching as! Bool else { return }
-        runningApplication.removeObserver(self, forKeyPath: "isFinishedLaunching")
+        removeObserver()
         addAndObserveWindows()
     }
 

alt-tab-macos/logic/Applications.swift

@@ -30,13 +30,15 @@ class Applications {
         var someAppsAreAlreadyTerminated = false
         for runningApp in runningApps {
             guard runningApp.bundleIdentifier != nil else { someAppsAreAlreadyTerminated = true; continue }
-            guard Applications.map[runningApp.processIdentifier] != nil else { continue }
+            guard let app = Applications.map[runningApp.processIdentifier] else { continue }
             var windowsToKeep = [Window]()
             for window in Windows.listRecentlyUsedFirst {
                 guard window.application.runningApplication.processIdentifier != runningApp.processIdentifier else { continue }
                 windowsToKeep.append(window)
             }
             Windows.listRecentlyUsedFirst = windowsToKeep
+            // some apps never finish launching; the observer leaks for them without this
+            app.removeObserver()
             Applications.map.removeValue(forKey: runningApp.processIdentifier)
             guard Windows.listRecentlyUsedFirst.count > 0 else { (App.shared as! App).hideUi(); return }
             // TODO: implement of more sophisticated way to decide which thumbnail gets focused on app quit