Disable unsupported_provider_value when a notifier returns "this"

fixes #2302

packages/riverpod_lint/lib/src/lints/unsupported_provider_value.dart

@@ -1,9 +1,19 @@
+import 'package:analyzer/dart/element/type.dart';
+import 'package:analyzer/dart/element/type_system.dart';
 import 'package:analyzer/error/listener.dart';
 import 'package:custom_lint_builder/custom_lint_builder.dart';
 import 'package:riverpod_analyzer_utils/riverpod_analyzer_utils.dart';
 
 import '../riverpod_custom_lint.dart';
 
+extension on StatefulProviderDeclaration {
+  /// Returns whether the value exposed by the provider is the newly created
+  /// Notifier itself.
+  bool get returnsSelf {
+    return valueType == node.declaredElement?.thisType;
+  }
+}
+
 class UnsupportedProviderValue extends RiverpodLintRule {
   const UnsupportedProviderValue() : super(code: _code);
 
@@ -21,16 +31,26 @@ class UnsupportedProviderValue extends RiverpodLintRule {
   ) {
     void checkCreatedType(GeneratorProviderDeclaration declaration) {
       String? invalidValueName;
+      if (notifierBaseType.isAssignableFromType(declaration.valueType)) {
+        invalidValueName = 'Notifier';
+      } else if (asyncNotifierBaseType
+          .isAssignableFromType(declaration.valueType)) {
+        invalidValueName = 'AsyncNotifier';
+      }
+
+      /// If a provider returns itself, we allow it. This is to enable
+      /// ChangeNotifier-like mutable state.
+      if (invalidValueName != null &&
+          declaration is StatefulProviderDeclaration &&
+          declaration.returnsSelf) {
+        return;
+      }
+
       if (stateNotifierType.isAssignableFromType(declaration.valueType)) {
         invalidValueName = 'StateNotifier';
       } else if (changeNotifierType
           .isAssignableFromType(declaration.valueType)) {
         invalidValueName = 'ChangeNotifier';
-      } else if (notifierBaseType.isAssignableFromType(declaration.valueType)) {
-        invalidValueName = 'Notifier';
-      } else if (asyncNotifierBaseType
-          .isAssignableFromType(declaration.valueType)) {
-        invalidValueName = 'AsyncNotifier';
       }
 
       if (invalidValueName != null) {

packages/riverpod_lint_flutter_test/test/goldens/lints/unsupported_provider_value.dart

@@ -22,6 +22,24 @@ class StateNotifierClass extends _$StateNotifierClass {
 Future<MyStateNotifier> stateNotifierAsync(StateNotifierAsyncRef ref) async =>
     MyStateNotifier();
 
+// Regression tests for https://github.com/rrousselGit/riverpod/issues/2302
+@riverpod
+class SelfNotifier extends _$SelfNotifier {
+  Future<SelfNotifier> build() async => this;
+}
+
+// Regression tests for https://github.com/rrousselGit/riverpod/issues/2302
+@riverpod
+class SyncSelfNotifier extends _$SyncSelfNotifier {
+  SyncSelfNotifier build() => this;
+}
+
+// Regression tests for https://github.com/rrousselGit/riverpod/issues/2302
+@riverpod
+class StreamSelfNotifier extends _$StreamSelfNotifier {
+  Stream<StreamSelfNotifier> build() => Stream.value(this);
+}
+
 @riverpod
 // expect_lint: unsupported_provider_value
 class StateNotifierClassAsync extends _$StateNotifierClassAsync {
@@ -48,6 +66,12 @@ class MyChangeNotifier extends ChangeNotifier {}
 // expect_lint: unsupported_provider_value
 MyNotifier notifier(NotifierRef ref) => MyNotifier();
 
+@riverpod
+// expect_lint: unsupported_provider_value
+MyAutoDisposeNotifier autoDisposeNotifier(AutoDisposeNotifierRef ref) {
+  return MyAutoDisposeNotifier();
+}
+
 @riverpod
 // expect_lint: unsupported_provider_value
 class NotifierClass extends _$NotifierClass {
@@ -59,6 +83,11 @@ class MyNotifier extends Notifier<int> {
   int build() => 0;
 }
 
+class MyAutoDisposeNotifier extends AutoDisposeNotifier<int> {
+  @override
+  int build() => 0;
+}
+
 @riverpod
 // expect_lint: unsupported_provider_value
 MyAsyncNotifier asyncNotifier(AsyncNotifierRef ref) => MyAsyncNotifier();