Switch debugAssertNotDisposed to be a static (#104772)

This reverts part of the change made in #103456 to expose a debug check for subclasses of ChangeNotifier to avoid code duplication. Instead of making debugAssertNotDisposed a public instance function, it is now a public static function. It makes it harder to call, slightly, but it means that everyone who implemented ChangeNotifier instead of extending it doesn't get broken.

packages/flutter/lib/src/foundation/change_notifier.dart

@@ -129,19 +129,22 @@ class ChangeNotifier implements Listenable {
   /// ```dart
   /// class MyNotifier with ChangeNotifier {
   ///   void doUpdate() {
-  ///     assert(debugAssertNotDisposed());
+  ///     assert(ChangeNotifier.debugAssertNotDisposed(this));
   ///     // ...
   ///   }
   /// }
   /// ```
   /// {@end-tool}
-  @protected
-  bool debugAssertNotDisposed() {
+  // This is static and not an instance method because too many people try to
+  // implement ChangeNotifier instead of extending it (and so it is too breaking
+  // to add a method, especially for debug).
+  static bool debugAssertNotDisposed(ChangeNotifier notifier) {
     assert(() {
-      if (_debugDisposed) {
+      if (notifier._debugDisposed) {
         throw FlutterError(
-          'A $runtimeType was used after being disposed.\n'
-          'Once you have called dispose() on a $runtimeType, it can no longer be used.',
+          'A ${notifier.runtimeType} was used after being disposed.\n'
+          'Once you have called dispose() on a ${notifier.runtimeType}, it '
+          'can no longer be used.',
         );
       }
       return true;
@@ -166,7 +169,7 @@ class ChangeNotifier implements Listenable {
   /// so, stopping that same work.
   @protected
   bool get hasListeners {
-    assert(debugAssertNotDisposed());
+    assert(ChangeNotifier.debugAssertNotDisposed(this));
     return _count > 0;
   }
 
@@ -198,7 +201,7 @@ class ChangeNotifier implements Listenable {
   ///    the list of closures that are notified when the object changes.
   @override
   void addListener(VoidCallback listener) {
-    assert(debugAssertNotDisposed());
+    assert(ChangeNotifier.debugAssertNotDisposed(this));
     if (_count == _listeners.length) {
       if (_count == 0) {
         _listeners = List<VoidCallback?>.filled(1, null);
@@ -293,7 +296,7 @@ class ChangeNotifier implements Listenable {
   /// This method should only be called by the object's owner.
   @mustCallSuper
   void dispose() {
-    assert(debugAssertNotDisposed());
+    assert(ChangeNotifier.debugAssertNotDisposed(this));
     assert(() {
       _debugDisposed = true;
       return true;
@@ -321,7 +324,7 @@ class ChangeNotifier implements Listenable {
   @visibleForTesting
   @pragma('vm:notify-debugger-on-exception')
   void notifyListeners() {
-    assert(debugAssertNotDisposed());
+    assert(ChangeNotifier.debugAssertNotDisposed(this));
     if (_count == 0) {
       return;
     }

packages/flutter/lib/src/widgets/restoration.dart

@@ -473,7 +473,7 @@ abstract class RestorableProperty<T> extends ChangeNotifier {
 
   @override
   void dispose() {
-    assert(debugAssertNotDisposed()); // FYI, This uses ChangeNotifier's _debugDisposed, not _disposed.
+    assert(ChangeNotifier.debugAssertNotDisposed(this)); // FYI, This uses ChangeNotifier's _debugDisposed, not _disposed.
     _owner?._unregister(this);
     super.dispose();
     _disposed = true;
@@ -483,14 +483,14 @@ abstract class RestorableProperty<T> extends ChangeNotifier {
   String? _restorationId;
   RestorationMixin? _owner;
   void _register(String restorationId, RestorationMixin owner) {
-    assert(debugAssertNotDisposed());
+    assert(ChangeNotifier.debugAssertNotDisposed(this));
     assert(restorationId != null);
     assert(owner != null);
     _restorationId = restorationId;
     _owner = owner;
   }
   void _unregister() {
-    assert(debugAssertNotDisposed());
+    assert(ChangeNotifier.debugAssertNotDisposed(this));
     assert(_restorationId != null);
     assert(_owner != null);
     _restorationId = null;
@@ -503,14 +503,14 @@ abstract class RestorableProperty<T> extends ChangeNotifier {
   @protected
   State get state {
     assert(isRegistered);
-    assert(debugAssertNotDisposed());
+    assert(ChangeNotifier.debugAssertNotDisposed(this));
     return _owner!;
   }
 
   /// Whether this property is currently registered with a [RestorationMixin].
   @protected
   bool get isRegistered {
-    assert(debugAssertNotDisposed());
+    assert(ChangeNotifier.debugAssertNotDisposed(this));
     return _restorationId != null;
   }
 }

packages/flutter/lib/src/widgets/shortcuts.dart

@@ -1092,7 +1092,7 @@ class ShortcutRegistry with ChangeNotifier {
   ///
   /// Returns a copy: modifying the returned map will have no effect.
   Map<ShortcutActivator, Intent> get shortcuts {
-    assert(debugAssertNotDisposed());
+    assert(ChangeNotifier.debugAssertNotDisposed(this));
     return <ShortcutActivator, Intent>{
       for (final MapEntry<ShortcutRegistryEntry, Map<ShortcutActivator, Intent>> entry in _tokenShortcuts.entries)
         ...entry.value,
@@ -1123,7 +1123,7 @@ class ShortcutRegistry with ChangeNotifier {
   ///  * [ShortcutRegistryEntry.dispose], a function used to remove the set of
   ///    shortcuts associated with a particular entry.
   ShortcutRegistryEntry addAll(Map<ShortcutActivator, Intent> value) {
-    assert(debugAssertNotDisposed());
+    assert(ChangeNotifier.debugAssertNotDisposed(this));
     final ShortcutRegistryEntry entry = ShortcutRegistryEntry._(this);
     _tokenShortcuts[entry] = value;
     assert(_debugCheckForDuplicates());
@@ -1191,7 +1191,7 @@ class ShortcutRegistry with ChangeNotifier {
   // Replaces all the shortcuts associated with the given entry from this
   // registry.
   void _replaceAll(ShortcutRegistryEntry entry, Map<ShortcutActivator, Intent> value) {
-    assert(debugAssertNotDisposed());
+    assert(ChangeNotifier.debugAssertNotDisposed(this));
     assert(_debugCheckTokenIsValid(entry));
     _tokenShortcuts[entry] = value;
     assert(_debugCheckForDuplicates());

packages/flutter/test/foundation/change_notifier_test.dart

@@ -475,6 +475,29 @@ void main() {
     );
   });
 
+  test('Calling debugAssertNotDisposed works as intended', () {
+    final TestNotifier testNotifier = TestNotifier();
+    expect(ChangeNotifier.debugAssertNotDisposed(testNotifier), isTrue);
+    testNotifier.dispose();
+    FlutterError? error;
+    try {
+      ChangeNotifier.debugAssertNotDisposed(testNotifier);
+    } on FlutterError catch (e) {
+      error = e;
+    }
+    expect(error, isNotNull);
+    expect(error, isFlutterError);
+    expect(
+      error!.toStringDeep(),
+      equalsIgnoringHashCodes(
+        'FlutterError\n'
+        '   A TestNotifier was used after being disposed.\n'
+        '   Once you have called dispose() on a TestNotifier, it can no\n'
+        '   longer be used.\n',
+      ),
+    );
+  });
+
   test('notifyListener can be called recursively', () {
     final Counter counter = Counter();
     final List<String> log = <String>[];