Add `RestorableEnumN<T>` and `RestorableEnum<T>` to restorable primitive types (#115050)

* Add RestorableEnumN and RestorableEnum to restorable primitive types

* Review Changes

* Change to assert if not part of the valid set.

* Assert if default value isn't in the enum

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

@@ -496,3 +496,177 @@ class RestorableTextEditingController extends RestorableChangeNotifier<TextEditi
     return value.text;
   }
 }
+
+/// A [RestorableProperty] that knows how to store and restore a nullable [Enum]
+/// type.
+///
+/// {@macro flutter.widgets.RestorableNum}
+///
+/// The values are serialized using the name of the enum, obtained using the
+/// [EnumName.name] extension accessor.
+///
+/// The represented value is accessible via the [value] getter. The set of
+/// values in the enum are accessible via the [values] getter. Since
+/// [RestorableEnumN] allows null, this set will include null.
+///
+/// See also:
+///
+/// * [RestorableEnum], a class similar to this one that knows how to store and
+///   restore non-nullable [Enum] types.
+class RestorableEnumN<T extends Enum> extends RestorableValue<T?> {
+  /// Creates a [RestorableEnumN].
+  ///
+  /// {@macro flutter.widgets.RestorableNum.constructor}
+  RestorableEnumN(T? defaultValue, { required Iterable<T> values })
+    : assert(defaultValue == null || values.contains(defaultValue),
+        'Default value $defaultValue not found in $T values: $values'),
+      _defaultValue = defaultValue,
+      values = values.toSet();
+
+  @override
+  T? createDefaultValue() => _defaultValue;
+  final T? _defaultValue;
+
+  @override
+  set value(T? newValue) {
+    assert(newValue == null || values.contains(newValue),
+      'Attempted to set an unknown enum value "$newValue" that is not null, or '
+      'in the valid set of enum values for the $T type: '
+      '${values.map<String>((T value) => value.name).toSet()}');
+    super.value = newValue;
+  }
+
+  /// The set of non-null values that this [RestorableEnumN] may represent.
+  ///
+  /// This is a required field that supplies the enum values that are serialized
+  /// and restored.
+  ///
+  /// If a value is encountered that is not null or a value in this set,
+  /// [fromPrimitives] will assert when restoring.
+  ///
+  /// It is typically set to the `values` list of the enum type.
+  ///
+  /// In addition to this set, because [RestorableEnumN] allows nullable values,
+  /// null is also a valid value, even though it doesn't appear in this set.
+  ///
+  /// {@tool snippet} For example, to create a [RestorableEnumN] with an
+  /// [AxisDirection] enum value, with a default value of null, you would build
+  /// it like the code below:
+  ///
+  /// ```dart
+  /// RestorableEnumN<AxisDirection> axis = RestorableEnumN<AxisDirection>(null, values: AxisDirection.values);
+  /// ```
+  /// {@end-tool}
+  Set<T> values;
+
+  @override
+  void didUpdateValue(T? oldValue) {
+    notifyListeners();
+  }
+
+  @override
+  T? fromPrimitives(Object? data) {
+    if (data == null) {
+      return null;
+    }
+    if (data is String) {
+      for (final T allowed in values) {
+        if (allowed.name == data) {
+          return allowed;
+        }
+      }
+      assert(false,
+        'Attempted to set an unknown enum value "$data" that is not null, or '
+        'in the valid set of enum values for the $T type: '
+        '${values.map<String>((T value) => value.name).toSet()}');
+    }
+    return _defaultValue;
+  }
+
+  @override
+  Object? toPrimitives() => value?.name;
+}
+
+
+/// A [RestorableProperty] that knows how to store and restore an [Enum]
+/// type.
+///
+/// {@macro flutter.widgets.RestorableNum}
+///
+/// The values are serialized using the name of the enum, obtained using the
+/// [EnumName.name] extension accessor.
+///
+/// The represented value is accessible via the [value] getter.
+///
+/// See also:
+///
+/// * [RestorableEnumN], a class similar to this one that knows how to store and
+///   restore nullable [Enum] types.
+class RestorableEnum<T extends Enum> extends RestorableValue<T> {
+  /// Creates a [RestorableEnum].
+  ///
+  /// {@macro flutter.widgets.RestorableNum.constructor}
+  RestorableEnum(T defaultValue, { required Iterable<T> values })
+    : assert(values.contains(defaultValue),
+        'Default value $defaultValue not found in $T values: $values'),
+      _defaultValue = defaultValue,
+      values = values.toSet();
+
+  @override
+  T createDefaultValue() => _defaultValue;
+  final T _defaultValue;
+
+  @override
+  set value(T newValue) {
+    assert(values.contains(newValue),
+      'Attempted to set an unknown enum value "$newValue" that is not in the '
+      'valid set of enum values for the $T type: '
+      '${values.map<String>((T value) => value.name).toSet()}');
+
+    super.value = newValue;
+  }
+
+  /// The set of values that this [RestorableEnum] may represent.
+  ///
+  /// This is a required field that supplies the possible enum values that can
+  /// be serialized and restored.
+  ///
+  /// If a value is encountered that is not in this set, [fromPrimitives] will
+  /// assert when restoring.
+  ///
+  /// It is typically set to the `values` list of the enum type.
+  ///
+  /// {@tool snippet} For example, to create a [RestorableEnum] with an
+  /// [AxisDirection] enum value, with a default value of [AxisDirection.up],
+  /// you would build it like the code below:
+  ///
+  /// ```dart
+  /// RestorableEnum<AxisDirection> axis = RestorableEnum<AxisDirection>(AxisDirection.up, values: AxisDirection.values);
+  /// ```
+  /// {@end-tool}
+  Set<T> values;
+
+  @override
+  void didUpdateValue(T? oldValue) {
+    notifyListeners();
+  }
+
+  @override
+  T fromPrimitives(Object? data) {
+    if (data != null && data is String) {
+      for (final T allowed in values) {
+        if (allowed.name == data) {
+          return allowed;
+        }
+      }
+      assert(false,
+        'Attempted to restore an unknown enum value "$data" that is not in the '
+        'valid set of enum values for the $T type: '
+        '${values.map<String>((T value) => value.name).toSet()}');
+    }
+    return _defaultValue;
+  }
+
+  @override
+  Object toPrimitives() => value.name;
+}