Dump logs on failing devicelab test to recipe artifact location (#74378)

dev/devicelab/bin/tasks/module_test_ios.dart

@@ -5,6 +5,7 @@
 import 'dart:io';
 
 import 'package:flutter_devicelab/framework/framework.dart';
+import 'package:flutter_devicelab/framework/host_agent.dart';
 import 'package:flutter_devicelab/framework/ios.dart';
 import 'package:flutter_devicelab/framework/task_result.dart';
 import 'package:flutter_devicelab/framework/utils.dart';
@@ -292,6 +293,8 @@ Future<void> main() async {
       section('Run platform unit tests');
       await testWithNewIOSSimulator('TestAdd2AppSim', (String deviceId) {
         simulatorDeviceId = deviceId;
+
+        final String resultBundlePath = path.join(hostAgent.dumpDirectory.path, 'module_test_ios-objc-${DateTime.now().toLocal().toIso8601String()}');
         return inDirectory(objectiveCHostApp, () =>
           exec(
             'xcodebuild',
@@ -304,6 +307,8 @@ Future<void> main() async {
               'Debug',
               '-destination',
               'id=$deviceId',
+              '-resultBundlePath',
+              resultBundlePath,
               'test',
               'CODE_SIGNING_ALLOWED=NO',
               'CODE_SIGNING_REQUIRED=NO',

dev/devicelab/lib/framework/host_agent.dart

@@ -0,0 +1,44 @@
+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:file/file.dart';
+import 'package:file/local.dart';
+import 'package:meta/meta.dart';
+import 'package:platform/platform.dart';
+
+/// The current host machine running the tests.
+HostAgent get hostAgent => HostAgent(platform: const LocalPlatform(), fileSystem: const LocalFileSystem());
+
+/// Host machine running the tests.
+class HostAgent {
+  HostAgent({@required Platform platform, @required FileSystem fileSystem})
+      : _platform = platform,
+        _fileSystem = fileSystem;
+
+  final Platform _platform;
+  final FileSystem _fileSystem;
+
+  /// Creates a directory to dump file artifacts.
+  Directory get dumpDirectory {
+    if (_dumpDirectory == null) {
+      // Set in LUCI recipe.
+      final String directoryPath = _platform.environment['FLUTTER_LOGS_DIR'];
+      if (directoryPath == null) {
+        _dumpDirectory = _fileSystem.systemTempDirectory.createTempSync('flutter_test_logs.');
+        print('Created tmp dump directory ${_dumpDirectory.path}');
+      } else {
+        _dumpDirectory = _fileSystem.directory(directoryPath)..createSync(recursive: true);
+        print('Found FLUTTER_LOGS_DIR dump directory ${_dumpDirectory.path}');
+      }
+    }
+    return _dumpDirectory;
+  }
+
+  static Directory _dumpDirectory;
+
+  @visibleForTesting
+  void resetDumpDirectory() {
+    _dumpDirectory = null;
+  }
+}

dev/devicelab/test/host_agent_test.dart

@@ -0,0 +1,51 @@
+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:file/file.dart';
+import 'package:file/memory.dart';
+import 'package:flutter_devicelab/framework/host_agent.dart';
+import 'package:platform/platform.dart';
+
+import 'common.dart';
+
+void main() {
+  FileSystem fs;
+  setUp(() {
+    fs = MemoryFileSystem();
+    hostAgent.resetDumpDirectory();
+  });
+
+  tearDown(() {
+    hostAgent.resetDumpDirectory();
+  });
+
+  group('dump directory', () {
+    test('set by environment', () async {
+      final Directory environmentDir = fs.directory(fs.path.join('home', 'logs'));
+      final FakePlatform fakePlatform = FakePlatform(
+        environment: <String, String>{'FLUTTER_LOGS_DIR': environmentDir.path},
+        operatingSystem: 'windows',
+      );
+      final HostAgent agent = HostAgent(platform: fakePlatform, fileSystem: fs);
+
+      expect(agent.dumpDirectory.existsSync(), isTrue);
+      expect(agent.dumpDirectory.path, environmentDir.path);
+    });
+
+    test('not set by environment', () async {
+      final FakePlatform fakePlatform = FakePlatform(environment: <String, String>{}, operatingSystem: 'windows');
+      final HostAgent agent = HostAgent(platform: fakePlatform, fileSystem: fs);
+
+      expect(agent.dumpDirectory.existsSync(), isTrue);
+    });
+
+    test('is the same between host agent instances', () async {
+      final FakePlatform fakePlatform = FakePlatform(environment: <String, String>{}, operatingSystem: 'windows');
+      final HostAgent agent1 = HostAgent(platform: fakePlatform, fileSystem: fs);
+      final HostAgent agent2 = HostAgent(platform: fakePlatform, fileSystem: fs);
+
+      expect(agent1.dumpDirectory.path, agent2.dumpDirectory.path);
+    });
+  });
+}