Prevent GC of value during async eval (#9885)

Author: srawlins

packages/devtools_app/release_notes/NEXT_RELEASE_NOTES.md

@@ -35,7 +35,8 @@ TODO: Remove this section if there are not any updates.
 
 ## Debugger updates
 
-TODO: Remove this section if there are not any updates.
+* Prevent values from being garbage-collected, while being evaluated.
+  [#9885](https://github.com/flutter/devtools/pull/9885)
 
 ## Network profiler updates
 

packages/devtools_app_shared/CHANGELOG.md

@@ -6,6 +6,7 @@ found in the LICENSE file or at https://developers.google.com/open-source/licens
 ## 0.5.2-wip
 * Fix a `RangeError` thrown by `SplitPane` when the number of children
   changes between rebuilds.
+* Fix garbage collection issues with the result list in `asyncEval` on both native VM and web.
 * The minimum Dart SDK version is bumped to 3.11.0.
 * The minimum Flutter SDK version is bumped to 3.41.0.
 

packages/devtools_app_shared/lib/src/service/eval_on_dart_library.dart

@@ -5,15 +5,15 @@
 // This code is directly based on src/io/flutter/inspector/EvalOnDartLibrary.java
 // If you add a method to this class you should also add it to EvalOnDartLibrary.java
 import 'dart:async';
-import 'dart:core' hide Error;
 import 'dart:core' as core;
+import 'dart:core' hide Error;
 import 'dart:math';
 
 import 'package:flutter/foundation.dart';
 import 'package:logging/logging.dart';
 import 'package:meta/meta.dart';
-import 'package:vm_service/vm_service.dart' hide Error;
 import 'package:vm_service/vm_service.dart' as vm_service;
+import 'package:vm_service/vm_service.dart' hide Error;
 
 import '../utils/auto_dispose.dart';
 import 'service_manager.dart';
@@ -429,6 +429,22 @@ class EvalOnDartLibrary extends DisposableController
     await safeEval(
       '() async {'
       '  final reader = widgetInspectorService.toObject("$readerId", "$readerGroup") as List;'
+      '  /* Keep a strong reference to `reader` in the target app to prevent it'
+      '     from being garbage collected by Chrome/VM before the future resolves.'
+      '     Without this, the reader is only weakly referenced by the inspector'
+      '     service and is aggressively GCed, causing a TypeError/TimeoutException'
+      '     or failing the assertion that the retrieved result length is 1 or 2.'
+      '     We use Future.delayed in a loop instead of Timer because Future is in'
+      '     dart:core and guaranteed to be resolved without requiring dart:async. */'
+      '  bool isDone = false;'
+      '  () async {'
+      '    int bufferTicks = 0;'
+      '    /* Stop pinning after a 1-second buffer when the future has completed. */'
+      '    while (!isDone && ++bufferTicks <=20) {'
+      '      final _ = reader;'
+      '      await Future.delayed(const Duration(milliseconds: 50));'
+      '    }'
+      '  }();'
       '  try {'
       // Cast as dynamic so that it is possible to await Future<void>
       '    dynamic result = ($expression) as dynamic;'
@@ -437,6 +453,7 @@ class EvalOnDartLibrary extends DisposableController
       '    reader.add(err);'
       '    reader.add(stack);'
       '  } finally {'
+      '    isDone = true;'
       '    postEvent("future_completed", {"future_id": $futureId, "client_id": $_clientId});'
       '  }'
       '}()',