Add leak checker. (#4109)

Author: davidmorgan

.github/workflows/dart.yml

@@ -13,3 +13,7 @@ stages:
     os:
     - linux
     - windows
+- leak_check:
+  - group:
+    - command: ../tool/leak_check.sh
+    sdk: dev

build_runner_core/mono_pkg.yaml

@@ -0,0 +1,39 @@
+// Copyright (c) 2025, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:io';
+
+import 'invalidation_tester.dart';
+
+/// Checks for memory leaks.
+///
+/// Runs many incremental builds, prints the average increase in memory usage
+/// per build.
+///
+/// Run using `tool/leak_check.sh`.
+void main(List<String> arguments) async {
+  final tester = InvalidationTester(testIsRunning: false);
+
+  tester.sources(['a.1']);
+
+  tester.builder(from: '.1', to: '.2')
+    ..reads('.1')
+    ..resolvesOther('a.1')
+    ..writes('.2');
+
+  await tester.build();
+  await tester.build(change: 'a.1');
+
+  // `.dart_tool/build_resolvers/sdk.sum` will be calculated and written if it
+  // does not yet exist, leading to very different memory usage. Users should
+  // run with the arg `setup` first to make sure this has happened.
+  if (arguments.contains('setup')) return;
+
+  final before = ProcessInfo.currentRss;
+  for (var i = 0; i != 5000; ++i) {
+    await tester.build(change: 'a.1');
+  }
+  final after = ProcessInfo.currentRss;
+  print((after - before) ~/ 5000);
+}

build_runner_core/test/invalidation/invalidation_leak_checker.dart

@@ -22,6 +22,8 @@ import 'package:test/test.dart';
 /// to the path `lib/a.dart`; all names map to the package `pkg`. "Hidden" asset
 /// IDs under `.dart_tool` are mapped back to the same namespace.
 class InvalidationTester {
+  final bool testIsRunning;
+
   /// The source assets on disk before the first build.
   final Set<AssetId> _sourceAssets = {};
 
@@ -65,6 +67,8 @@ class InvalidationTester {
   /// Output number, for writing outputs that are different.
   int _outputNumber = 0;
 
+  InvalidationTester({this.testIsRunning = true});
+
   /// Starts logging test setup.
   ///
   /// Useful if test setup is random or generated.
@@ -231,11 +235,13 @@ class InvalidationTester {
       testingBuilderConfig: false,
     );
     final logString = log.toString();
-    printOnFailure(
-      '=== build log #${++_buildNumber} ===\n\n'
-      '${_setupLog.map((l) => '  $l\n').join('')}'
-      '${logString.trimAndIndent}',
-    );
+    if (testIsRunning) {
+      printOnFailure(
+        '=== build log #${++_buildNumber} ===\n\n'
+        '${_setupLog.map((l) => '  $l\n').join('')}'
+        '${logString.trimAndIndent}',
+      );
+    }
     if (_logSetup) _setupLog.clear();
     readerWriter = testBuildResult.readerWriter;