Respect allowlisted count of leaks. (#128823)

Contributes to dart-lang/leak_tracker#59

Author: polina-c

packages/flutter/test/foundation/leak_tracking.dart

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:core';
+
 import 'package:flutter/foundation.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:leak_tracker/leak_tracker.dart';
@@ -143,28 +145,56 @@ class LeakCleaner {
 
   final LeakTrackingTestConfig config;
 
+  static Map<(String, LeakType), int> _countByClassAndType(Leaks leaks) {
+    final Map<(String, LeakType), int> result = <(String, LeakType), int>{};
+
+    for (final MapEntry<LeakType, List<LeakReport>> entry in leaks.byType.entries) {
+      for (final LeakReport leak in entry.value) {
+        final (String, LeakType) classAndType = (leak.type, entry.key);
+        result[classAndType] = (result[classAndType] ?? 0) + 1;
+      }
+    }
+    return result;
+  }
+
   Leaks clean(Leaks leaks) {
+    final Map<(String, LeakType), int> countByClassAndType = _countByClassAndType(leaks);
+
     final Leaks result =  Leaks(<LeakType, List<LeakReport>>{
       for (final LeakType leakType in leaks.byType.keys)
-        leakType: leaks.byType[leakType]!.where((LeakReport leak) => _shouldReportLeak(leakType, leak)).toList()
+        leakType: leaks.byType[leakType]!.where((LeakReport leak) => _shouldReportLeak(leakType, leak, countByClassAndType)).toList()
     });
     return result;
   }
 
   /// Returns true if [leak] should be reported as failure.
-  bool _shouldReportLeak(LeakType leakType, LeakReport leak) {
+  bool _shouldReportLeak(LeakType leakType, LeakReport leak, Map<(String, LeakType), int> countByClassAndType) {
     // Tracking for non-GCed is temporarily disabled.
     // TODO(polina-c): turn on tracking for non-GCed after investigating existing leaks.
     if (leakType != LeakType.notDisposed) {
       return false;
     }
 
+    final String leakingClass = leak.type;
+    final (String, LeakType) classAndType = (leakingClass, leakType);
+
+    bool isAllowedForClass(Map<String, int?> allowList) {
+      if (!allowList.containsKey(leakingClass)) {
+        return false;
+      }
+      final int? allowedCount = allowList[leakingClass];
+      if (allowedCount == null) {
+        return true;
+      }
+      return allowedCount >= countByClassAndType[classAndType]!;
+    }
+
     switch (leakType) {
       case LeakType.notDisposed:
-        return !config.notDisposedAllowList.containsKey(leak.type);
+        return !isAllowedForClass(config.notDisposedAllowList);
       case LeakType.notGCed:
       case LeakType.gcedLate:
-        return !config.notGCedAllowList.containsKey(leak.type);
+        return !isAllowedForClass(config.notGCedAllowList);
     }
   }
 }

packages/flutter/test/foundation/leak_tracking_test.dart

@@ -29,9 +29,22 @@ Future<void> main() async {
     expect(cleanedLeaks.total, 1);
   });
 
-  group('Leak tracking works for non-web', () {
+  test('$LeakCleaner catches extra leaks', () {
+    Leaks leaks = _leaksOfAllTypes();
+    final LeakReport leak = leaks.notDisposed.first;
+    leaks.notDisposed.add(leak);
+
+    final LeakTrackingTestConfig config = LeakTrackingTestConfig(
+      notDisposedAllowList: <String, int?>{leak.type: 1},
+    );
+    leaks = LeakCleaner(config).clean(leaks);
+
+    expect(leaks.notDisposed, hasLength(2));
+  });
+
+  group('Leak tracking works for non-web, and', () {
     testWidgetsWithLeakTracking(
-      'Leak tracker respects all allow lists',
+      'respects all allow lists',
       (WidgetTester tester) async {
         await tester.pumpWidget(_StatelessLeakingWidget());
       },
@@ -41,7 +54,41 @@ Future<void> main() async {
       ),
     );
 
-    group('Leak tracker respects notGCed allow lists', () {
+    testWidgetsWithLeakTracking(
+      'respects count in allow lists',
+      (WidgetTester tester) async {
+        await tester.pumpWidget(_StatelessLeakingWidget());
+      },
+      leakTrackingConfig: LeakTrackingTestConfig(
+        notDisposedAllowList: <String, int?>{_leakTrackedClassName: 1},
+        notGCedAllowList: <String, int?>{_leakTrackedClassName: 1},
+      ),
+    );
+
+    group('fails if number or leaks is more than allowed', () {
+      // This test cannot run inside other tests because test nesting is forbidden.
+      // So, `expect` happens outside the tests, in `tearDown`.
+      late Leaks leaks;
+
+      testWidgetsWithLeakTracking(
+        'for $_StatelessLeakingWidget',
+        (WidgetTester tester) async {
+          await tester.pumpWidget(_StatelessLeakingWidget());
+          await tester.pumpWidget(_StatelessLeakingWidget());
+        },
+        leakTrackingConfig: LeakTrackingTestConfig(
+          onLeaks: (Leaks theLeaks) {
+            leaks = theLeaks;
+          },
+          failTestOnLeaks: false,
+          notDisposedAllowList: <String, int?>{_leakTrackedClassName: 1},
+        ),
+      );
+
+      tearDown(() => _verifyLeaks(leaks, expectedNotDisposed: 2));
+    });
+
+    group('respects notGCed allow lists', () {
       // These tests cannot run inside other tests because test nesting is forbidden.
       // So, `expect` happens outside the tests, in `tearDown`.
       late Leaks leaks;
@@ -63,8 +110,8 @@ Future<void> main() async {
       tearDown(() => _verifyLeaks(leaks, expectedNotDisposed: 1));
     });
 
-    group('Leak tracker catches that', () {
-      // These tests cannot run inside other tests because test nesting is forbidden.
+    group('catches that', () {
+      // These test cannot run inside other tests because test nesting is forbidden.
       // So, `expect` happens outside the tests, in `tearDown`.
       late Leaks leaks;