Expose isolateId for engine (#10823)

shell/platform/darwin/ios/framework/Headers/FlutterEngine.h

@@ -242,6 +242,13 @@ FLUTTER_EXPORT
  */
 @property(nonatomic, readonly) NSObject<FlutterBinaryMessenger>* binaryMessenger;
 
+/**
+ * The UI Isolate ID of of the engine.
+ *
+ * This property will be nil if the engine is not running.
+ */
+@property(nonatomic, readonly, copy) NSString* isolateId;
+
 @end
 
 #endif  // FLUTTER_FLUTTERENGINE_H_

shell/platform/darwin/ios/framework/Source/FlutterEngine.mm

@@ -31,6 +31,8 @@
 // Maintains a dictionary of plugin names that have registered with the engine.  Used by
 // FlutterEngineRegistrar to implement a FlutterPluginRegistrar.
 @property(nonatomic, readonly) NSMutableDictionary* pluginPublications;
+
+@property(nonatomic, readwrite, copy) NSString* isolateId;
 @end
 
 @interface FlutterEngineRegistrar : NSObject <FlutterPluginRegistrar>
@@ -171,6 +173,7 @@
 
 - (void)destroyContext {
   [self resetChannels];
+  self.isolateId = nil;
   _shell.reset();
   _threadHost.Reset();
   _platformViewsController.reset();
@@ -233,6 +236,13 @@
 // Channels get a reference to the engine, and therefore need manual
 // cleanup for proper collection.
 - (void)setupChannels {
+  // This will be invoked once the shell is done setting up and the isolate ID
+  // for the UI isolate is available.
+  [_binaryMessenger setMessageHandlerOnChannel:@"flutter/isolate"
+                          binaryMessageHandler:^(NSData* message, FlutterBinaryReply reply) {
+                            self.isolateId = [[FlutterStringCodec sharedInstance] decode:message];
+                          }];
+
   _localizationChannel.reset([[FlutterMethodChannel alloc]
          initWithName:@"flutter/localization"
       binaryMessenger:self.binaryMessenger

testing/scenario_app/ios/Scenarios/Scenarios.xcodeproj/project.pbxproj

@@ -23,6 +23,7 @@
 		248D76DA22E388380012F0C1 /* main.m in Sources */ = {isa = PBXBuildFile; fileRef = 248D76D922E388380012F0C1 /* main.m */; };
 		248D76E422E388380012F0C1 /* ScenariosTests.m in Sources */ = {isa = PBXBuildFile; fileRef = 248D76E322E388380012F0C1 /* ScenariosTests.m */; };
 		248D76EF22E388380012F0C1 /* ScenariosUITests.m in Sources */ = {isa = PBXBuildFile; fileRef = 248D76EE22E388380012F0C1 /* ScenariosUITests.m */; };
+		248FDFC422FE7CD0009CC7CD /* FlutterEngineTest.m in Sources */ = {isa = PBXBuildFile; fileRef = 248FDFC322FE7CD0009CC7CD /* FlutterEngineTest.m */; };
 /* End PBXBuildFile section */
 
 /* Begin PBXContainerItemProxy section */
@@ -95,6 +96,7 @@
 		248D76EA22E388380012F0C1 /* ScenariosUITests.xctest */ = {isa = PBXFileReference; explicitFileType = wrapper.cfbundle; includeInIndex = 0; path = ScenariosUITests.xctest; sourceTree = BUILT_PRODUCTS_DIR; };
 		248D76EE22E388380012F0C1 /* ScenariosUITests.m */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.objc; path = ScenariosUITests.m; sourceTree = "<group>"; };
 		248D76F022E388380012F0C1 /* Info.plist */ = {isa = PBXFileReference; lastKnownFileType = text.plist.xml; path = Info.plist; sourceTree = "<group>"; };
+		248FDFC322FE7CD0009CC7CD /* FlutterEngineTest.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = FlutterEngineTest.m; sourceTree = "<group>"; };
 /* End PBXFileReference section */
 
 /* Begin PBXFrameworksBuildPhase section */
@@ -162,6 +164,7 @@
 		248D76E222E388380012F0C1 /* ScenariosTests */ = {
 			isa = PBXGroup;
 			children = (
+				248FDFC322FE7CD0009CC7CD /* FlutterEngineTest.m */,
 				0DB781FC22EA2C0300E9B371 /* FlutterViewControllerTest.m */,
 				248D76E322E388380012F0C1 /* ScenariosTests.m */,
 				248D76E522E388380012F0C1 /* Info.plist */,
@@ -329,6 +332,7 @@
 			files = (
 				248D76E422E388380012F0C1 /* ScenariosTests.m in Sources */,
 				0DB7820222EA493B00E9B371 /* FlutterViewControllerTest.m in Sources */,
+				248FDFC422FE7CD0009CC7CD /* FlutterEngineTest.m in Sources */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;
 		};

testing/scenario_app/ios/Scenarios/ScenariosTests/FlutterEngineTest.m

+// Copyright 2013 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 <Flutter/Flutter.h>
+#import <XCTest/XCTest.h>
+#import "AppDelegate.h"
+
+@interface FlutterEngineTest : XCTestCase
+@end
+
+@implementation FlutterEngineTest
+
+- (void)testIsolateId {
+  FlutterEngine* engine = [[FlutterEngine alloc] initWithName:@"test" project:nil];
+  XCTAssertNil(engine.isolateId);
+  [self keyValueObservingExpectationForObject:engine keyPath:@"isolateId" handler:nil];
+
+  XCTAssertTrue([engine runWithEntrypoint:nil]);
+
+  [self waitForExpectationsWithTimeout:30.0 handler:nil];
+
+  XCTAssertNotNil(engine.isolateId);
+  XCTAssertTrue([engine.isolateId hasPrefix:@"isolates/"]);
+
+  [engine destroyContext];
+
+  XCTAssertNil(engine.isolateId);
+}
+
+@end