[pigeon] Fix Object arguments in Swift and C++ (#3020)

Fixes a warning in generated Swift output when an argument is of type Object. This is blocking flutter/plugins#6914 since we check our macOS and iOS plugin code for warnings in CI.

Rather than add a Dart generator unit test for this one specific case, I tightened the Swift compilation settings for our test plugin to treat warnings as errors (per flutter/flutter#59116 (comment)) to catch the entire class of errors, and added echo* variants for Object to make sure this one then showed up.

Incidental fixes:

I had to make a similar fix to the Dart generator for a similar warning with casting to Object?, which we'd never noticed because we weren't analyzing any generated code that returning Object or Object? before.
I had to make a change to the C++ generator so that generation would succeed, because it turned out we had no handling at all of Object in the C++ generator, causing it to throw. I'm not sure this is the output I'll keep for C++ (thus the TODO), but it's the simple fix to make it work at all.
Fixes flutter/flutter#117994
Part of flutter/flutter#59116

packages/pigeon/CHANGELOG.md

@@ -1,3 +1,9 @@
+## 4.2.16
+
+* [swift] Fixes warnings with `Object` parameters.
+* [dart] Fixes warnings with `Object` return values.
+* [c++] Generation of APIs that use `Object` no longer fails.
+
 ## 4.2.15
 
 * Relocates generator classes. (Reverted)

packages/pigeon/lib/cpp_generator.dart

@@ -547,6 +547,11 @@ const flutter::StandardMessageCodec& ${api.name}::GetCodec() {
                       // ... then declare the arg as a reference to that local.
                       indent.writeln(
                           'const auto* $argName = $encodableArgName.IsNull() ? nullptr : &$valueVarName;');
+                    } else if (hostType.datatype == 'flutter::EncodableValue') {
+                      // Generic objects just pass the EncodableValue through
+                      // directly.
+                      indent.writeln(
+                          'const auto* $argName = &$encodableArgName;');
                     } else if (hostType.isBuiltin) {
                       indent.writeln(
                           'const auto* $argName = std::get_if<${hostType.datatype}>(&$encodableArgName);');
@@ -564,6 +569,13 @@ const flutter::StandardMessageCodec& ${api.name}::GetCodec() {
                       // requires an int64_t so that it can handle any case.
                       indent.writeln(
                           'const int64_t $argName = $encodableArgName.LongValue();');
+                    } else if (hostType.datatype == 'flutter::EncodableValue') {
+                      // Generic objects just pass the EncodableValue through
+                      // directly. This creates an alias just to avoid having to
+                      // special-case the argName/encodableArgName distinction
+                      // at a higher level.
+                      indent
+                          .writeln('const auto& $argName = $encodableArgName;');
                     } else if (hostType.isBuiltin) {
                       indent.writeln(
                           'const auto& $argName = std::get<${hostType.datatype}>($encodableArgName);');
@@ -902,6 +914,7 @@ String? _baseCppTypeForBuiltinDartType(TypeDeclaration type) {
     'Float64List': 'std::vector<double>',
     'Map': 'flutter::EncodableMap',
     'List': 'flutter::EncodableList',
+    'Object': 'flutter::EncodableValue',
   };
   if (cppTypeForDartTypeMap.containsKey(type.baseName)) {
     return cppTypeForDartTypeMap[type.baseName];
@@ -931,6 +944,8 @@ String _unownedArgumentType(HostDatatype type) {
   if (isString || _isPodType(type)) {
     return type.isNullable ? 'const $baseType*' : baseType;
   }
+  // TODO(stuartmorgan): Consider special-casing `Object?` here, so that there
+  // aren't two ways of representing null (nullptr or an isNull EncodableValue).
   return type.isNullable ? 'const $baseType*' : 'const $baseType&';
 }
 

packages/pigeon/lib/dart_generator.dart

@@ -230,13 +230,17 @@ final BinaryMessenger? _binaryMessenger;
           indent.writeln('binaryMessenger: _binaryMessenger);');
         });
         final String returnType = _makeGenericTypeArguments(func.returnType);
-        final String castCall = _makeGenericCastCall(func.returnType);
+        final String genericCastCall = _makeGenericCastCall(func.returnType);
         const String accessor = 'replyList[0]';
-        final String nullHandler =
+        // Avoid warnings from pointlessly casting to `Object?`.
-            func.returnType.isNullable ? (castCall.isEmpty ? '' : '?') : '!';
+        final String nullablyTypedAccessor =
+            returnType == 'Object' ? accessor : '($accessor as $returnType?)';
+        final String nullHandler = func.returnType.isNullable
+            ? (genericCastCall.isEmpty ? '' : '?')
+            : '!';
         final String returnStatement = func.returnType.isVoid
             ? 'return;'
-            : 'return ($accessor as $returnType?)$nullHandler$castCall;';
+            : 'return $nullablyTypedAccessor$nullHandler$genericCastCall;';
         indent.format('''
 final List<Object?>? replyList =
 \t\tawait channel.send($sendArgument) as List<Object?>?;

packages/pigeon/lib/generator_tools.dart

@@ -9,7 +9,7 @@ import 'dart:mirrors';
 import 'ast.dart';
 
 /// The current version of pigeon. This must match the version in pubspec.yaml.
-const String pigeonVersion = '4.2.15';
+const String pigeonVersion = '4.2.16';
 
 /// Read all the content from [stdin] to a String.
 String readStdin() {

packages/pigeon/lib/swift_generator.dart

@@ -365,6 +365,9 @@ String _castForceUnwrap(String value, TypeDeclaration type, Root root) {
     final String nullableConditionPrefix =
         type.isNullable ? '$value == nil ? nil : ' : '';
     return '$nullableConditionPrefix${_swiftTypeForDartType(type)}(rawValue: $value as! Int)$forceUnwrap';
+  } else if (type.baseName == 'Object') {
+    // Special-cased to avoid warnings about using 'as' with Any.
+    return type.isNullable ? value : '$value!';
   } else {
     final String castUnwrap = type.isNullable ? '?' : '!';
     return '$value as$castUnwrap ${_swiftTypeForDartType(type)}';

packages/pigeon/pigeons/core_tests.dart

@@ -125,6 +125,10 @@ abstract class HostIntegrationCoreApi {
   @ObjCSelector('echoUint8List:')
   Uint8List echoUint8List(Uint8List aUint8List);
 
+  /// Returns the passed in generic Object.
+  @ObjCSelector('echoObject:')
+  Object echoObject(Object anObject);
+
   // ========== Syncronous nullable method tests ==========
 
   /// Returns the inner `aString` value from the wrapped object, to test
@@ -162,6 +166,10 @@ abstract class HostIntegrationCoreApi {
   @ObjCSelector('echoNullableUint8List:')
   Uint8List? echoNullableUint8List(Uint8List? aNullableUint8List);
 
+  /// Returns the passed in generic Object.
+  @ObjCSelector('echoNullableObject:')
+  Object? echoNullableObject(Object? aNullableObject);
+
   // ========== Asyncronous method tests ==========
 
   /// A no-op function taking no arguments and returning no value, to sanity

packages/pigeon/platform_tests/alternate_language_test_plugin/android/src/main/java/com/example/alternate_language_test_plugin/AlternateLanguageTestPlugin.java

@@ -72,6 +72,11 @@ public class AlternateLanguageTestPlugin implements FlutterPlugin, HostIntegrati
     return aUint8List;
   }
 
+  @Override
+  public @NonNull Object echoObject(@NonNull Object anObject) {
+    return anObject;
+  }
+
   @Override
   public @Nullable String extractNestedNullableString(@NonNull AllNullableTypesWrapper wrapper) {
     return wrapper.getValues().getANullableString();
@@ -124,6 +129,11 @@ public class AlternateLanguageTestPlugin implements FlutterPlugin, HostIntegrati
     return aNullableUint8List;
   }
 
+  @Override
+  public @Nullable Object echoNullableObject(@Nullable Object aNullableObject) {
+    return aNullableObject;
+  }
+
   @Override
   public void noopAsync(Result<Void> result) {
     result.success(null);

packages/pigeon/platform_tests/alternate_language_test_plugin/android/src/main/java/com/example/alternate_language_test_plugin/CoreTests.java

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
-// Autogenerated from Pigeon (v4.2.15), do not edit directly.
+// Autogenerated from Pigeon (v4.2.16), do not edit directly.
 // See also: https://pub.dev/packages/pigeon
 
 package com.example.alternate_language_test_plugin;
@@ -713,12 +713,9 @@ public class CoreTests {
           return AllNullableTypes.fromList((ArrayList<Object>) readValue(buffer));
 
         case (byte) 129:
-          return AllNullableTypes.fromList((ArrayList<Object>) readValue(buffer));
-
-        case (byte) 130:
           return AllNullableTypesWrapper.fromList((ArrayList<Object>) readValue(buffer));
 
-        case (byte) 131:
+        case (byte) 130:
           return AllTypes.fromList((ArrayList<Object>) readValue(buffer));
 
         default:
@@ -731,14 +728,11 @@ public class CoreTests {
       if (value instanceof AllNullableTypes) {
         stream.write(128);
         writeValue(stream, ((AllNullableTypes) value).toList());
-      } else if (value instanceof AllNullableTypes) {
-        stream.write(129);
-        writeValue(stream, ((AllNullableTypes) value).toList());
       } else if (value instanceof AllNullableTypesWrapper) {
-        stream.write(130);
+        stream.write(129);
         writeValue(stream, ((AllNullableTypesWrapper) value).toList());
       } else if (value instanceof AllTypes) {
-        stream.write(131);
+        stream.write(130);
         writeValue(stream, ((AllTypes) value).toList());
       } else {
         super.writeValue(stream, value);
@@ -780,6 +774,9 @@ public class CoreTests {
     /** Returns the passed in Uint8List. */
     @NonNull
     byte[] echoUint8List(@NonNull byte[] aUint8List);
+    /** Returns the passed in generic Object. */
+    @NonNull
+    Object echoObject(@NonNull Object anObject);
     /**
      * Returns the inner `aString` value from the wrapped object, to test sending of nested objects.
      */
@@ -811,6 +808,9 @@ public class CoreTests {
     /** Returns the passed in Uint8List. */
     @Nullable
     byte[] echoNullableUint8List(@Nullable byte[] aNullableUint8List);
+    /** Returns the passed in generic Object. */
+    @Nullable
+    Object echoNullableObject(@Nullable Object aNullableObject);
     /**
      * A no-op function taking no arguments and returning no value, to sanity test basic
      * asynchronous calling.
@@ -1072,6 +1072,35 @@ public class CoreTests {
           channel.setMessageHandler(null);
         }
       }
+      {
+        BasicMessageChannel<Object> channel =
+            new BasicMessageChannel<>(
+                binaryMessenger,
+                "dev.flutter.pigeon.HostIntegrationCoreApi.echoObject",
+                getCodec());
+        if (api != null) {
+          channel.setMessageHandler(
+              (message, reply) -> {
+                ArrayList wrapped = new ArrayList<>();
+                try {
+                  ArrayList<Object> args = (ArrayList<Object>) message;
+                  assert args != null;
+                  Object anObjectArg = args.get(0);
+                  if (anObjectArg == null) {
+                    throw new NullPointerException("anObjectArg unexpectedly null.");
+                  }
+                  Object output = api.echoObject(anObjectArg);
+                  wrapped.add(0, output);
+                } catch (Error | RuntimeException exception) {
+                  ArrayList<Object> wrappedError = wrapError(exception);
+                  wrapped = wrappedError;
+                }
+                reply.reply(wrapped);
+              });
+        } else {
+          channel.setMessageHandler(null);
+        }
+      }
       {
         BasicMessageChannel<Object> channel =
             new BasicMessageChannel<>(
@@ -1292,6 +1321,32 @@ public class CoreTests {
           channel.setMessageHandler(null);
         }
       }
+      {
+        BasicMessageChannel<Object> channel =
+            new BasicMessageChannel<>(
+                binaryMessenger,
+                "dev.flutter.pigeon.HostIntegrationCoreApi.echoNullableObject",
+                getCodec());
+        if (api != null) {
+          channel.setMessageHandler(
+              (message, reply) -> {
+                ArrayList wrapped = new ArrayList<>();
+                try {
+                  ArrayList<Object> args = (ArrayList<Object>) message;
+                  assert args != null;
+                  Object aNullableObjectArg = args.get(0);
+                  Object output = api.echoNullableObject(aNullableObjectArg);
+                  wrapped.add(0, output);
+                } catch (Error | RuntimeException exception) {
+                  ArrayList<Object> wrappedError = wrapError(exception);
+                  wrapped = wrappedError;
+                }
+                reply.reply(wrapped);
+              });
+        } else {
+          channel.setMessageHandler(null);
+        }
+      }
       {
         BasicMessageChannel<Object> channel =
             new BasicMessageChannel<>(

packages/pigeon/platform_tests/alternate_language_test_plugin/ios/Classes/AlternateLanguageTestPlugin.m

@@ -63,6 +63,10 @@
   return aUint8List;
 }
 
+- (nullable id)echoObject:(id)anObject error:(FlutterError *_Nullable *_Nonnull)error {
+  return anObject;
+}
+
 - (nullable NSString *)extractNestedNullableStringFrom:(AllNullableTypesWrapper *)wrapper
                                                  error:(FlutterError *_Nullable *_Nonnull)error {
   return wrapper.values.aNullableString;
@@ -114,6 +118,11 @@
   return aNullableUint8List;
 }
 
+- (nullable id)echoNullableObject:(nullable id)aNullableObject
+                            error:(FlutterError *_Nullable *_Nonnull)error {
+  return aNullableObject;
+}
+
 - (void)noopAsyncWithCompletion:(void (^)(FlutterError *_Nullable))completion {
   completion(nil);
 }

packages/pigeon/platform_tests/alternate_language_test_plugin/ios/Classes/CoreTests.gen.h

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
-// Autogenerated from Pigeon (v4.2.15), do not edit directly.
+// Autogenerated from Pigeon (v4.2.16), do not edit directly.
 // See also: https://pub.dev/packages/pigeon
 #import <Foundation/Foundation.h>
 @protocol FlutterBinaryMessenger;
@@ -131,6 +131,10 @@ NSObject<FlutterMessageCodec> *HostIntegrationCoreApiGetCodec(void);
 /// @return `nil` only when `error != nil`.
 - (nullable FlutterStandardTypedData *)echoUint8List:(FlutterStandardTypedData *)aUint8List
                                                error:(FlutterError *_Nullable *_Nonnull)error;
+/// Returns the passed in generic Object.
+///
+/// @return `nil` only when `error != nil`.
+- (nullable id)echoObject:(id)anObject error:(FlutterError *_Nullable *_Nonnull)error;
 /// Returns the inner `aString` value from the wrapped object, to test
 /// sending of nested objects.
 - (nullable NSString *)extractNestedNullableStringFrom:(AllNullableTypesWrapper *)wrapper
@@ -166,6 +170,9 @@ NSObject<FlutterMessageCodec> *HostIntegrationCoreApiGetCodec(void);
 - (nullable FlutterStandardTypedData *)
     echoNullableUint8List:(nullable FlutterStandardTypedData *)aNullableUint8List
                     error:(FlutterError *_Nullable *_Nonnull)error;
+/// Returns the passed in generic Object.
+- (nullable id)echoNullableObject:(nullable id)aNullableObject
+                            error:(FlutterError *_Nullable *_Nonnull)error;
 /// A no-op function taking no arguments and returning no value, to sanity
 /// test basic asynchronous calling.
 - (void)noopAsyncWithCompletion:(void (^)(FlutterError *_Nullable))completion;

packages/pigeon/platform_tests/alternate_language_test_plugin/ios/Classes/CoreTests.gen.m

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
-// Autogenerated from Pigeon (v4.2.15), do not edit directly.
+// Autogenerated from Pigeon (v4.2.16), do not edit directly.
 // See also: https://pub.dev/packages/pigeon
 #import "CoreTests.gen.h"
 #import <Flutter/Flutter.h>
@@ -220,12 +220,9 @@ static id GetNullableObjectAtIndex(NSArray *array, NSInteger key) {
       return [AllNullableTypes fromList:[self readValue]];
 
     case 129:
-      return [AllNullableTypes fromList:[self readValue]];
-
-    case 130:
       return [AllNullableTypesWrapper fromList:[self readValue]];
 
-    case 131:
+    case 130:
       return [AllTypes fromList:[self readValue]];
 
     default:
@@ -241,14 +238,11 @@ static id GetNullableObjectAtIndex(NSArray *array, NSInteger key) {
   if ([value isKindOfClass:[AllNullableTypes class]]) {
     [self writeByte:128];
     [self writeValue:[value toList]];
-  } else if ([value isKindOfClass:[AllNullableTypes class]]) {
+  } else if ([value isKindOfClass:[AllNullableTypesWrapper class]]) {
     [self writeByte:129];
     [self writeValue:[value toList]];
-  } else if ([value isKindOfClass:[AllNullableTypesWrapper class]]) {
-    [self writeByte:130];
-    [self writeValue:[value toList]];
   } else if ([value isKindOfClass:[AllTypes class]]) {
-    [self writeByte:131];
+    [self writeByte:130];
     [self writeValue:[value toList]];
   } else {
     [super writeValue:value];
@@ -470,6 +464,27 @@ void HostIntegrationCoreApiSetup(id<FlutterBinaryMessenger> binaryMessenger,
       [channel setMessageHandler:nil];
     }
   }
+  /// Returns the passed in generic Object.
+  {
+    FlutterBasicMessageChannel *channel = [[FlutterBasicMessageChannel alloc]
+           initWithName:@"dev.flutter.pigeon.HostIntegrationCoreApi.echoObject"
+        binaryMessenger:binaryMessenger
+                  codec:HostIntegrationCoreApiGetCodec()];
+    if (api) {
+      NSCAssert([api respondsToSelector:@selector(echoObject:error:)],
+                @"HostIntegrationCoreApi api (%@) doesn't respond to @selector(echoObject:error:)",
+                api);
+      [channel setMessageHandler:^(id _Nullable message, FlutterReply callback) {
+        NSArray *args = message;
+        id arg_anObject = GetNullableObjectAtIndex(args, 0);
+        FlutterError *error;
+        id output = [api echoObject:arg_anObject error:&error];
+        callback(wrapResult(output, error));
+      }];
+    } else {
+      [channel setMessageHandler:nil];
+    }
+  }
   /// Returns the inner `aString` value from the wrapped object, to test
   /// sending of nested objects.
   {
@@ -656,6 +671,28 @@ void HostIntegrationCoreApiSetup(id<FlutterBinaryMessenger> binaryMessenger,
       [channel setMessageHandler:nil];
     }
   }
+  /// Returns the passed in generic Object.
+  {
+    FlutterBasicMessageChannel *channel = [[FlutterBasicMessageChannel alloc]
+           initWithName:@"dev.flutter.pigeon.HostIntegrationCoreApi.echoNullableObject"
+        binaryMessenger:binaryMessenger
+                  codec:HostIntegrationCoreApiGetCodec()];
+    if (api) {
+      NSCAssert([api respondsToSelector:@selector(echoNullableObject:error:)],
+                @"HostIntegrationCoreApi api (%@) doesn't respond to "
+                @"@selector(echoNullableObject:error:)",
+                api);
+      [channel setMessageHandler:^(id _Nullable message, FlutterReply callback) {
+        NSArray *args = message;
+        id arg_aNullableObject = GetNullableObjectAtIndex(args, 0);
+        FlutterError *error;
+        id output = [api echoNullableObject:arg_aNullableObject error:&error];
+        callback(wrapResult(output, error));
+      }];
+    } else {
+      [channel setMessageHandler:nil];
+    }
+  }
   /// A no-op function taking no arguments and returning no value, to sanity
   /// test basic asynchronous calling.
   {

packages/pigeon/platform_tests/shared_test_plugin_code/lib/integration_tests.dart

@@ -351,6 +351,19 @@ void runPigeonIntegrationTests(TargetGenerator targetGenerator) {
       expect(receivedUint8List, sentUint8List);
     });
 
+    testWidgets('generic Objects serialize and deserialize correctly',
+        (WidgetTester _) async {
+      final HostIntegrationCoreApi api = HostIntegrationCoreApi();
+      const Object sentString = "I'm a computer";
+      final Object receivedString = await api.echoObject(sentString);
+      expect(receivedString, sentString);
+
+      // Echo a second type as well to ensure the handling is generic.
+      const Object sentInt = 42;
+      final Object receivedInt = await api.echoObject(sentInt);
+      expect(receivedInt, sentInt);
+    });
+
     testWidgets('Nullable Ints serialize and deserialize correctly',
         (WidgetTester _) async {
       final HostIntegrationCoreApi api = HostIntegrationCoreApi();
@@ -449,6 +462,27 @@ void runPigeonIntegrationTests(TargetGenerator targetGenerator) {
           await api.echoNullableUint8List(null);
       expect(receivedNullUint8List, null);
     });
+
+    testWidgets('generic nullable Objects serialize and deserialize correctly',
+        (WidgetTester _) async {
+      final HostIntegrationCoreApi api = HostIntegrationCoreApi();
+      const Object sentString = "I'm a computer";
+      final Object? receivedString = await api.echoNullableObject(sentString);
+      expect(receivedString, sentString);
+
+      // Echo a second type as well to ensure the handling is generic.
+      const Object sentInt = 42;
+      final Object? receivedInt = await api.echoNullableObject(sentInt);
+      expect(receivedInt, sentInt);
+    });
+
+    testWidgets('Null generic Objects serialize and deserialize correctly',
+        (WidgetTester _) async {
+      final HostIntegrationCoreApi api = HostIntegrationCoreApi();
+
+      final Object? receivedNullObject = await api.echoNullableObject(null);
+      expect(receivedNullObject, null);
+    });
   });
 
   group('Host async API tests', () {

packages/pigeon/platform_tests/shared_test_plugin_code/lib/src/generated/core_tests.gen.dart

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
-// Autogenerated from Pigeon (v4.2.15), do not edit directly.
+// Autogenerated from Pigeon (v4.2.16), do not edit directly.
 // See also: https://pub.dev/packages/pigeon
 // ignore_for_file: public_member_api_docs, non_constant_identifier_names, avoid_as, unused_import, unnecessary_parenthesis, prefer_null_aware_operators, omit_local_variable_types, unused_shown_name, unnecessary_import
 import 'dart:async';
@@ -205,14 +205,11 @@ class _HostIntegrationCoreApiCodec extends StandardMessageCodec {
     if (value is AllNullableTypes) {
       buffer.putUint8(128);
       writeValue(buffer, value.encode());
-    } else if (value is AllNullableTypes) {
+    } else if (value is AllNullableTypesWrapper) {
       buffer.putUint8(129);
       writeValue(buffer, value.encode());
-    } else if (value is AllNullableTypesWrapper) {
-      buffer.putUint8(130);
-      writeValue(buffer, value.encode());
     } else if (value is AllTypes) {
-      buffer.putUint8(131);
+      buffer.putUint8(130);
       writeValue(buffer, value.encode());
     } else {
       super.writeValue(buffer, value);
@@ -226,12 +223,9 @@ class _HostIntegrationCoreApiCodec extends StandardMessageCodec {
         return AllNullableTypes.decode(readValue(buffer)!);
 
       case 129:
-        return AllNullableTypes.decode(readValue(buffer)!);
-
-      case 130:
         return AllNullableTypesWrapper.decode(readValue(buffer)!);
 
-      case 131:
+      case 130:
         return AllTypes.decode(readValue(buffer)!);
 
       default:
@@ -489,6 +483,34 @@ class HostIntegrationCoreApi {
     }
   }
 
+  /// Returns the passed in generic Object.
+  Future<Object> echoObject(Object arg_anObject) async {
+    final BasicMessageChannel<Object?> channel = BasicMessageChannel<Object?>(
+        'dev.flutter.pigeon.HostIntegrationCoreApi.echoObject', codec,
+        binaryMessenger: _binaryMessenger);
+    final List<Object?>? replyList =
+        await channel.send(<Object?>[arg_anObject]) as List<Object?>?;
+    if (replyList == null) {
+      throw PlatformException(
+        code: 'channel-error',
+        message: 'Unable to establish connection on channel.',
+      );
+    } else if (replyList.length > 1) {
+      throw PlatformException(
+        code: replyList[0]! as String,
+        message: replyList[1] as String?,
+        details: replyList[2],
+      );
+    } else if (replyList[0] == null) {
+      throw PlatformException(
+        code: 'null-error',
+        message: 'Host platform returned null value for non-null return value.',
+      );
+    } else {
+      return replyList[0]!;
+    }
+  }
+
   /// Returns the inner `aString` value from the wrapped object, to test
   /// sending of nested objects.
   Future<String?> extractNestedNullableString(
@@ -694,6 +716,29 @@ class HostIntegrationCoreApi {
     }
   }
 
+  /// Returns the passed in generic Object.
+  Future<Object?> echoNullableObject(Object? arg_aNullableObject) async {
+    final BasicMessageChannel<Object?> channel = BasicMessageChannel<Object?>(
+        'dev.flutter.pigeon.HostIntegrationCoreApi.echoNullableObject', codec,
+        binaryMessenger: _binaryMessenger);
+    final List<Object?>? replyList =
+        await channel.send(<Object?>[arg_aNullableObject]) as List<Object?>?;
+    if (replyList == null) {
+      throw PlatformException(
+        code: 'channel-error',
+        message: 'Unable to establish connection on channel.',
+      );
+    } else if (replyList.length > 1) {
+      throw PlatformException(
+        code: replyList[0]! as String,
+        message: replyList[1] as String?,
+        details: replyList[2],
+      );
+    } else {
+      return replyList[0];
+    }
+  }
+
   /// A no-op function taking no arguments and returning no value, to sanity
   /// test basic asynchronous calling.
   Future<void> noopAsync() async {

packages/pigeon/platform_tests/test_plugin/android/src/main/kotlin/com/example/test_plugin/CoreTests.gen.kt

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 // 
-// Autogenerated from Pigeon (v4.2.15), do not edit directly.
+// Autogenerated from Pigeon (v4.2.16), do not edit directly.
 // See also: https://pub.dev/packages/pigeon
 
 package com.example.test_plugin
@@ -169,16 +169,11 @@ private object HostIntegrationCoreApiCodec : StandardMessageCodec() {
         }
       }
       129.toByte() -> {
-        return (readValue(buffer) as? List<Any?>)?.let {
-          AllNullableTypes.fromList(it)
-        }
-      }
-      130.toByte() -> {
         return (readValue(buffer) as? List<Any?>)?.let {
           AllNullableTypesWrapper.fromList(it)
         }
       }
-      131.toByte() -> {
+      130.toByte() -> {
         return (readValue(buffer) as? List<Any?>)?.let {
           AllTypes.fromList(it)
         }
@@ -192,16 +187,12 @@ private object HostIntegrationCoreApiCodec : StandardMessageCodec() {
         stream.write(128)
         writeValue(stream, value.toList())
       }
-      is AllNullableTypes -> {
+      is AllNullableTypesWrapper -> {
         stream.write(129)
         writeValue(stream, value.toList())
       }
-      is AllNullableTypesWrapper -> {
-        stream.write(130)
-        writeValue(stream, value.toList())
-      }
       is AllTypes -> {
-        stream.write(131)
+        stream.write(130)
         writeValue(stream, value.toList())
       }
       else -> super.writeValue(stream, value)
@@ -237,6 +228,8 @@ interface HostIntegrationCoreApi {
   fun echoString(aString: String): String
   /** Returns the passed in Uint8List. */
   fun echoUint8List(aUint8List: ByteArray): ByteArray
+  /** Returns the passed in generic Object. */
+  fun echoObject(anObject: Any): Any
   /**
    * Returns the inner `aString` value from the wrapped object, to test
    * sending of nested objects.
@@ -259,6 +252,8 @@ interface HostIntegrationCoreApi {
   fun echoNullableString(aNullableString: String?): String?
   /** Returns the passed in Uint8List. */
   fun echoNullableUint8List(aNullableUint8List: ByteArray?): ByteArray?
+  /** Returns the passed in generic Object. */
+  fun echoNullableObject(aNullableObject: Any?): Any?
   /**
    * A no-op function taking no arguments and returning no value, to sanity
    * test basic asynchronous calling.
@@ -437,6 +432,24 @@ interface HostIntegrationCoreApi {
           channel.setMessageHandler(null)
         }
       }
+      run {
+        val channel = BasicMessageChannel<Any?>(binaryMessenger, "dev.flutter.pigeon.HostIntegrationCoreApi.echoObject", codec)
+        if (api != null) {
+          channel.setMessageHandler { message, reply ->
+            var wrapped = listOf<Any?>()
+            try {
+              val args = message as List<Any?>
+              val anObjectArg = args[0] as Any
+              wrapped = listOf<Any?>(api.echoObject(anObjectArg))
+            } catch (exception: Error) {
+              wrapped = wrapError(exception)
+            }
+            reply.reply(wrapped)
+          }
+        } else {
+          channel.setMessageHandler(null)
+        }
+      }
       run {
         val channel = BasicMessageChannel<Any?>(binaryMessenger, "dev.flutter.pigeon.HostIntegrationCoreApi.extractNestedNullableString", codec)
         if (api != null) {
@@ -583,6 +596,24 @@ interface HostIntegrationCoreApi {
           channel.setMessageHandler(null)
         }
       }
+      run {
+        val channel = BasicMessageChannel<Any?>(binaryMessenger, "dev.flutter.pigeon.HostIntegrationCoreApi.echoNullableObject", codec)
+        if (api != null) {
+          channel.setMessageHandler { message, reply ->
+            var wrapped = listOf<Any?>()
+            try {
+              val args = message as List<Any?>
+              val aNullableObjectArg = args[0] as? Any
+              wrapped = listOf<Any?>(api.echoNullableObject(aNullableObjectArg))
+            } catch (exception: Error) {
+              wrapped = wrapError(exception)
+            }
+            reply.reply(wrapped)
+          }
+        } else {
+          channel.setMessageHandler(null)
+        }
+      }
       run {
         val channel = BasicMessageChannel<Any?>(binaryMessenger, "dev.flutter.pigeon.HostIntegrationCoreApi.noopAsync", codec)
         if (api != null) {

packages/pigeon/platform_tests/test_plugin/android/src/main/kotlin/com/example/test_plugin/TestPlugin.kt

@@ -64,6 +64,10 @@ class TestPlugin: FlutterPlugin, HostIntegrationCoreApi {
     return aUint8List
   }
 
+  override fun echoObject(anObject: Any): Any {
+    return anObject
+  }
+
   override fun extractNestedNullableString(wrapper: AllNullableTypesWrapper): String? {
     return wrapper.values.aNullableString
   }
@@ -75,22 +79,31 @@ class TestPlugin: FlutterPlugin, HostIntegrationCoreApi {
   override fun sendMultipleNullableTypes(aNullableBool: Boolean?, aNullableInt: Long?, aNullableString: String?): AllNullableTypes {
     return AllNullableTypes(aNullableBool = aNullableBool, aNullableInt = aNullableInt, aNullableString = aNullableString)
   }
+
   override fun echoNullableInt(aNullableInt: Long?): Long? {
     return aNullableInt
   }
+
   override fun echoNullableDouble(aNullableDouble: Double?): Double? {
     return aNullableDouble
   }
+
   override fun echoNullableBool(aNullableBool: Boolean?): Boolean? {
     return aNullableBool
   }
+
   override fun echoNullableString(aNullableString: String?): String? {
     return aNullableString
   }
+
   override fun echoNullableUint8List(aNullableUint8List: ByteArray?): ByteArray? {
     return aNullableUint8List
   }
 
+  override fun echoNullableObject(aNullableObject: Any?): Any? {
+    return aNullableObject
+  }
+
   override fun noopAsync(callback: () -> Unit) {
     callback()
   }

packages/pigeon/platform_tests/test_plugin/example/ios/Podfile

@@ -41,5 +41,9 @@ end
 post_install do |installer|
   installer.pods_project.targets.each do |target|
     flutter_additional_ios_build_settings(target)
+
+    target.build_configurations.each do |config|
+      config.build_settings['SWIFT_TREAT_WARNINGS_AS_ERRORS'] = 'YES'
+    end
   end
 end

packages/pigeon/platform_tests/test_plugin/example/macos/Podfile

@@ -40,5 +40,9 @@ end
 post_install do |installer|
   installer.pods_project.targets.each do |target|
     flutter_additional_macos_build_settings(target)
+
+    target.build_configurations.each do |config|
+      config.build_settings['SWIFT_TREAT_WARNINGS_AS_ERRORS'] = 'YES'
+    end
   end
 end

packages/pigeon/platform_tests/test_plugin/ios/Classes/CoreTests.gen.swift

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 // 
-// Autogenerated from Pigeon (v4.2.15), do not edit directly.
+// Autogenerated from Pigeon (v4.2.16), do not edit directly.
 // See also: https://pub.dev/packages/pigeon
 
 import Foundation
@@ -178,10 +178,8 @@ private class HostIntegrationCoreApiCodecReader: FlutterStandardReader {
       case 128:
         return AllNullableTypes.fromList(self.readValue() as! [Any])      
       case 129:
-        return AllNullableTypes.fromList(self.readValue() as! [Any])      
-      case 130:
         return AllNullableTypesWrapper.fromList(self.readValue() as! [Any])      
-      case 131:
+      case 130:
         return AllTypes.fromList(self.readValue() as! [Any])      
       default:
         return super.readValue(ofType: type)
@@ -194,14 +192,11 @@ private class HostIntegrationCoreApiCodecWriter: FlutterStandardWriter {
     if let value = value as? AllNullableTypes {
       super.writeByte(128)
       super.writeValue(value.toList())
-    } else if let value = value as? AllNullableTypes {
+    } else if let value = value as? AllNullableTypesWrapper {
       super.writeByte(129)
       super.writeValue(value.toList())
-    } else if let value = value as? AllNullableTypesWrapper {
-      super.writeByte(130)
-      super.writeValue(value.toList())
     } else if let value = value as? AllTypes {
-      super.writeByte(131)
+      super.writeByte(130)
       super.writeValue(value.toList())
     } else {
       super.writeValue(value)
@@ -247,6 +242,8 @@ protocol HostIntegrationCoreApi {
   func echoString(aString: String) -> String
   /// Returns the passed in Uint8List.
   func echoUint8List(aUint8List: FlutterStandardTypedData) -> FlutterStandardTypedData
+  /// Returns the passed in generic Object.
+  func echoObject(anObject: Any) -> Any
   /// Returns the inner `aString` value from the wrapped object, to test
   /// sending of nested objects.
   func extractNestedNullableString(wrapper: AllNullableTypesWrapper) -> String?
@@ -265,6 +262,8 @@ protocol HostIntegrationCoreApi {
   func echoNullableString(aNullableString: String?) -> String?
   /// Returns the passed in Uint8List.
   func echoNullableUint8List(aNullableUint8List: FlutterStandardTypedData?) -> FlutterStandardTypedData?
+  /// Returns the passed in generic Object.
+  func echoNullableObject(aNullableObject: Any?) -> Any?
   /// A no-op function taking no arguments and returning no value, to sanity
   /// test basic asynchronous calling.
   func noopAsync(completion: @escaping () -> Void)
@@ -385,6 +384,18 @@ class HostIntegrationCoreApiSetup {
     } else {
       echoUint8ListChannel.setMessageHandler(nil)
     }
+    /// Returns the passed in generic Object.
+    let echoObjectChannel = FlutterBasicMessageChannel(name: "dev.flutter.pigeon.HostIntegrationCoreApi.echoObject", binaryMessenger: binaryMessenger, codec: codec)
+    if let api = api {
+      echoObjectChannel.setMessageHandler { message, reply in
+        let args = message as! [Any?]
+        let anObjectArg = args[0]!
+        let result = api.echoObject(anObject: anObjectArg)
+        reply(wrapResult(result))
+      }
+    } else {
+      echoObjectChannel.setMessageHandler(nil)
+    }
     /// Returns the inner `aString` value from the wrapped object, to test
     /// sending of nested objects.
     let extractNestedNullableStringChannel = FlutterBasicMessageChannel(name: "dev.flutter.pigeon.HostIntegrationCoreApi.extractNestedNullableString", binaryMessenger: binaryMessenger, codec: codec)
@@ -485,6 +496,18 @@ class HostIntegrationCoreApiSetup {
     } else {
       echoNullableUint8ListChannel.setMessageHandler(nil)
     }
+    /// Returns the passed in generic Object.
+    let echoNullableObjectChannel = FlutterBasicMessageChannel(name: "dev.flutter.pigeon.HostIntegrationCoreApi.echoNullableObject", binaryMessenger: binaryMessenger, codec: codec)
+    if let api = api {
+      echoNullableObjectChannel.setMessageHandler { message, reply in
+        let args = message as! [Any?]
+        let aNullableObjectArg = args[0]
+        let result = api.echoNullableObject(aNullableObject: aNullableObjectArg)
+        reply(wrapResult(result))
+      }
+    } else {
+      echoNullableObjectChannel.setMessageHandler(nil)
+    }
     /// A no-op function taking no arguments and returning no value, to sanity
     /// test basic asynchronous calling.
     let noopAsyncChannel = FlutterBasicMessageChannel(name: "dev.flutter.pigeon.HostIntegrationCoreApi.noopAsync", binaryMessenger: binaryMessenger, codec: codec)

packages/pigeon/platform_tests/test_plugin/ios/Classes/TestPlugin.swift

@@ -59,6 +59,10 @@ public class TestPlugin: NSObject, FlutterPlugin, HostIntegrationCoreApi {
     return aUint8List
   }
 
+  func echoObject(anObject: Any) -> Any {
+    return anObject
+  }
+
   func extractNestedNullableString(wrapper: AllNullableTypesWrapper) -> String? {
     return wrapper.values.aNullableString;
   }
@@ -92,6 +96,10 @@ public class TestPlugin: NSObject, FlutterPlugin, HostIntegrationCoreApi {
     return aNullableUint8List
   }
 
+  func echoNullableObject(aNullableObject: Any?) -> Any? {
+    return aNullableObject
+  }
+
   func noopAsync(completion: @escaping () -> Void) {
     completion()
   }

packages/pigeon/platform_tests/test_plugin/macos/Classes/CoreTests.gen.swift

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 // 
-// Autogenerated from Pigeon (v4.2.15), do not edit directly.
+// Autogenerated from Pigeon (v4.2.16), do not edit directly.
 // See also: https://pub.dev/packages/pigeon
 
 import Foundation
@@ -178,10 +178,8 @@ private class HostIntegrationCoreApiCodecReader: FlutterStandardReader {
       case 128:
         return AllNullableTypes.fromList(self.readValue() as! [Any])      
       case 129:
-        return AllNullableTypes.fromList(self.readValue() as! [Any])      
-      case 130:
         return AllNullableTypesWrapper.fromList(self.readValue() as! [Any])      
-      case 131:
+      case 130:
         return AllTypes.fromList(self.readValue() as! [Any])      
       default:
         return super.readValue(ofType: type)
@@ -194,14 +192,11 @@ private class HostIntegrationCoreApiCodecWriter: FlutterStandardWriter {
     if let value = value as? AllNullableTypes {
       super.writeByte(128)
       super.writeValue(value.toList())
-    } else if let value = value as? AllNullableTypes {
+    } else if let value = value as? AllNullableTypesWrapper {
       super.writeByte(129)
       super.writeValue(value.toList())
-    } else if let value = value as? AllNullableTypesWrapper {
-      super.writeByte(130)
-      super.writeValue(value.toList())
     } else if let value = value as? AllTypes {
-      super.writeByte(131)
+      super.writeByte(130)
       super.writeValue(value.toList())
     } else {
       super.writeValue(value)
@@ -247,6 +242,8 @@ protocol HostIntegrationCoreApi {
   func echoString(aString: String) -> String
   /// Returns the passed in Uint8List.
   func echoUint8List(aUint8List: FlutterStandardTypedData) -> FlutterStandardTypedData
+  /// Returns the passed in generic Object.
+  func echoObject(anObject: Any) -> Any
   /// Returns the inner `aString` value from the wrapped object, to test
   /// sending of nested objects.
   func extractNestedNullableString(wrapper: AllNullableTypesWrapper) -> String?
@@ -265,6 +262,8 @@ protocol HostIntegrationCoreApi {
   func echoNullableString(aNullableString: String?) -> String?
   /// Returns the passed in Uint8List.
   func echoNullableUint8List(aNullableUint8List: FlutterStandardTypedData?) -> FlutterStandardTypedData?
+  /// Returns the passed in generic Object.
+  func echoNullableObject(aNullableObject: Any?) -> Any?
   /// A no-op function taking no arguments and returning no value, to sanity
   /// test basic asynchronous calling.
   func noopAsync(completion: @escaping () -> Void)
@@ -385,6 +384,18 @@ class HostIntegrationCoreApiSetup {
     } else {
       echoUint8ListChannel.setMessageHandler(nil)
     }
+    /// Returns the passed in generic Object.
+    let echoObjectChannel = FlutterBasicMessageChannel(name: "dev.flutter.pigeon.HostIntegrationCoreApi.echoObject", binaryMessenger: binaryMessenger, codec: codec)
+    if let api = api {
+      echoObjectChannel.setMessageHandler { message, reply in
+        let args = message as! [Any?]
+        let anObjectArg = args[0]!
+        let result = api.echoObject(anObject: anObjectArg)
+        reply(wrapResult(result))
+      }
+    } else {
+      echoObjectChannel.setMessageHandler(nil)
+    }
     /// Returns the inner `aString` value from the wrapped object, to test
     /// sending of nested objects.
     let extractNestedNullableStringChannel = FlutterBasicMessageChannel(name: "dev.flutter.pigeon.HostIntegrationCoreApi.extractNestedNullableString", binaryMessenger: binaryMessenger, codec: codec)
@@ -485,6 +496,18 @@ class HostIntegrationCoreApiSetup {
     } else {
       echoNullableUint8ListChannel.setMessageHandler(nil)
     }
+    /// Returns the passed in generic Object.
+    let echoNullableObjectChannel = FlutterBasicMessageChannel(name: "dev.flutter.pigeon.HostIntegrationCoreApi.echoNullableObject", binaryMessenger: binaryMessenger, codec: codec)
+    if let api = api {
+      echoNullableObjectChannel.setMessageHandler { message, reply in
+        let args = message as! [Any?]
+        let aNullableObjectArg = args[0]
+        let result = api.echoNullableObject(aNullableObject: aNullableObjectArg)
+        reply(wrapResult(result))
+      }
+    } else {
+      echoNullableObjectChannel.setMessageHandler(nil)
+    }
     /// A no-op function taking no arguments and returning no value, to sanity
     /// test basic asynchronous calling.
     let noopAsyncChannel = FlutterBasicMessageChannel(name: "dev.flutter.pigeon.HostIntegrationCoreApi.noopAsync", binaryMessenger: binaryMessenger, codec: codec)

packages/pigeon/platform_tests/test_plugin/macos/Classes/TestPlugin.swift

@@ -59,6 +59,10 @@ public class TestPlugin: NSObject, FlutterPlugin, HostIntegrationCoreApi {
     return aUint8List
   }
 
+  func echoObject(anObject: Any) -> Any {
+    return anObject
+  }
+
   func extractNestedNullableString(wrapper: AllNullableTypesWrapper) -> String? {
     return wrapper.values.aNullableString;
   }
@@ -92,6 +96,10 @@ public class TestPlugin: NSObject, FlutterPlugin, HostIntegrationCoreApi {
     return aNullableUint8List
   }
 
+  func echoNullableObject(aNullableObject: Any?) -> Any? {
+    return aNullableObject
+  }
+
   func noopAsync(completion: @escaping () -> Void) {
     completion()
   }

packages/pigeon/platform_tests/test_plugin/windows/pigeon/core_tests.gen.cpp

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
-// Autogenerated from Pigeon (v4.2.15), do not edit directly.
+// Autogenerated from Pigeon (v4.2.16), do not edit directly.
 // See also: https://pub.dev/packages/pigeon
 
 #undef _HAS_EXCEPTIONS
@@ -490,14 +490,10 @@ flutter::EncodableValue HostIntegrationCoreApiCodecSerializer::ReadValueOfType(
           std::get<flutter::EncodableList>(ReadValue(stream))));
 
     case 129:
-      return flutter::CustomEncodableValue(AllNullableTypes(
-          std::get<flutter::EncodableList>(ReadValue(stream))));
-
-    case 130:
       return flutter::CustomEncodableValue(AllNullableTypesWrapper(
           std::get<flutter::EncodableList>(ReadValue(stream))));
 
-    case 131:
+    case 130:
       return flutter::CustomEncodableValue(
           AllTypes(std::get<flutter::EncodableList>(ReadValue(stream))));
 
@@ -519,16 +515,8 @@ void HostIntegrationCoreApiCodecSerializer::WriteValue(
           stream);
       return;
     }
-    if (custom_value->type() == typeid(AllNullableTypes)) {
-      stream->WriteByte(129);
-      WriteValue(
-          flutter::EncodableValue(
-              std::any_cast<AllNullableTypes>(*custom_value).ToEncodableList()),
-          stream);
-      return;
-    }
     if (custom_value->type() == typeid(AllNullableTypesWrapper)) {
-      stream->WriteByte(130);
+      stream->WriteByte(129);
       WriteValue(flutter::EncodableValue(
                      std::any_cast<AllNullableTypesWrapper>(*custom_value)
                          .ToEncodableList()),
@@ -536,7 +524,7 @@ void HostIntegrationCoreApiCodecSerializer::WriteValue(
       return;
     }
     if (custom_value->type() == typeid(AllTypes)) {
-      stream->WriteByte(131);
+      stream->WriteByte(130);
       WriteValue(flutter::EncodableValue(
                      std::any_cast<AllTypes>(*custom_value).ToEncodableList()),
                  stream);
@@ -869,6 +857,43 @@ void HostIntegrationCoreApi::SetUp(flutter::BinaryMessenger* binary_messenger,
       channel->SetMessageHandler(nullptr);
     }
   }
+  {
+    auto channel =
+        std::make_unique<flutter::BasicMessageChannel<flutter::EncodableValue>>(
+            binary_messenger,
+            "dev.flutter.pigeon.HostIntegrationCoreApi.echoObject",
+            &GetCodec());
+    if (api != nullptr) {
+      channel->SetMessageHandler(
+          [api](const flutter::EncodableValue& message,
+                const flutter::MessageReply<flutter::EncodableValue>& reply) {
+            flutter::EncodableList wrapped;
+            try {
+              const auto& args = std::get<flutter::EncodableList>(message);
+              const auto& encodable_an_object_arg = args.at(0);
+              if (encodable_an_object_arg.IsNull()) {
+                reply(flutter::EncodableValue(
+                    WrapError("an_object_arg unexpectedly null.")));
+                return;
+              }
+              const auto& an_object_arg = encodable_an_object_arg;
+              ErrorOr<flutter::EncodableValue> output =
+                  api->EchoObject(an_object_arg);
+              if (output.has_error()) {
+                wrapped = WrapError(output.error());
+              } else {
+                wrapped.push_back(
+                    flutter::EncodableValue(std::move(output).TakeValue()));
+              }
+            } catch (const std::exception& exception) {
+              wrapped = WrapError(exception.what());
+            }
+            reply(flutter::EncodableValue(std::move(wrapped)));
+          });
+    } else {
+      channel->SetMessageHandler(nullptr);
+    }
+  }
   {
     auto channel = std::make_unique<
         flutter::BasicMessageChannel<flutter::EncodableValue>>(
@@ -1190,6 +1215,44 @@ void HostIntegrationCoreApi::SetUp(flutter::BinaryMessenger* binary_messenger,
       channel->SetMessageHandler(nullptr);
     }
   }
+  {
+    auto channel =
+        std::make_unique<flutter::BasicMessageChannel<flutter::EncodableValue>>(
+            binary_messenger,
+            "dev.flutter.pigeon.HostIntegrationCoreApi.echoNullableObject",
+            &GetCodec());
+    if (api != nullptr) {
+      channel->SetMessageHandler(
+          [api](const flutter::EncodableValue& message,
+                const flutter::MessageReply<flutter::EncodableValue>& reply) {
+            flutter::EncodableList wrapped;
+            try {
+              const auto& args = std::get<flutter::EncodableList>(message);
+              const auto& encodable_a_nullable_object_arg = args.at(0);
+              const auto* a_nullable_object_arg =
+                  &encodable_a_nullable_object_arg;
+              ErrorOr<std::optional<flutter::EncodableValue>> output =
+                  api->EchoNullableObject(a_nullable_object_arg);
+              if (output.has_error()) {
+                wrapped = WrapError(output.error());
+              } else {
+                auto output_optional = std::move(output).TakeValue();
+                if (output_optional) {
+                  wrapped.push_back(flutter::EncodableValue(
+                      std::move(output_optional).value()));
+                } else {
+                  wrapped.push_back(flutter::EncodableValue());
+                }
+              }
+            } catch (const std::exception& exception) {
+              wrapped = WrapError(exception.what());
+            }
+            reply(flutter::EncodableValue(std::move(wrapped)));
+          });
+    } else {
+      channel->SetMessageHandler(nullptr);
+    }
+  }
   {
     auto channel =
         std::make_unique<flutter::BasicMessageChannel<flutter::EncodableValue>>(

packages/pigeon/platform_tests/test_plugin/windows/pigeon/core_tests.gen.h

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
-// Autogenerated from Pigeon (v4.2.15), do not edit directly.
+// Autogenerated from Pigeon (v4.2.16), do not edit directly.
 // See also: https://pub.dev/packages/pigeon
 
 #ifndef PIGEON_CORE_TESTS_GEN_CORE_TESTS_PIGEONTEST_H_
@@ -283,6 +283,9 @@ class HostIntegrationCoreApi {
   // Returns the passed in Uint8List.
   virtual ErrorOr<std::vector<uint8_t>> EchoUint8List(
       const std::vector<uint8_t>& a_uint8_list) = 0;
+  // Returns the passed in generic Object.
+  virtual ErrorOr<flutter::EncodableValue> EchoObject(
+      const flutter::EncodableValue& an_object) = 0;
   // Returns the inner `aString` value from the wrapped object, to test
   // sending of nested objects.
   virtual ErrorOr<std::optional<std::string>> ExtractNestedNullableString(
@@ -310,6 +313,9 @@ class HostIntegrationCoreApi {
   // Returns the passed in Uint8List.
   virtual ErrorOr<std::optional<std::vector<uint8_t>>> EchoNullableUint8List(
       const std::vector<uint8_t>* a_nullable_uint8_list) = 0;
+  // Returns the passed in generic Object.
+  virtual ErrorOr<std::optional<flutter::EncodableValue>> EchoNullableObject(
+      const flutter::EncodableValue* a_nullable_object) = 0;
   // A no-op function taking no arguments and returning no value, to sanity
   // test basic asynchronous calling.
   virtual void NoopAsync(

packages/pigeon/platform_tests/test_plugin/windows/test_plugin.cpp

@@ -73,6 +73,11 @@ ErrorOr<std::vector<uint8_t>> TestPlugin::EchoUint8List(
   return a_uint8_list;
 }
 
+ErrorOr<flutter::EncodableValue> TestPlugin::EchoObject(
+    const flutter::EncodableValue& an_object) {
+  return an_object;
+}
+
 ErrorOr<std::optional<std::string>> TestPlugin::ExtractNestedNullableString(
     const AllNullableTypesWrapper& wrapper) {
   const std::string* inner_string = wrapper.values().a_nullable_string();
@@ -153,6 +158,14 @@ ErrorOr<std::optional<std::vector<uint8_t>>> TestPlugin::EchoNullableUint8List(
   return *a_nullable_uint8_list;
 };
 
+ErrorOr<std::optional<flutter::EncodableValue>> TestPlugin::EchoNullableObject(
+    const flutter::EncodableValue* a_nullable_object) {
+  if (!a_nullable_object) {
+    return std::nullopt;
+  }
+  return *a_nullable_object;
+};
+
 void TestPlugin::NoopAsync(
     std::function<void(std::optional<FlutterError> reply)> result) {
   result(std::nullopt);

packages/pigeon/platform_tests/test_plugin/windows/test_plugin.h

@@ -47,6 +47,8 @@ class TestPlugin : public flutter::Plugin,
       const std::string& a_string) override;
   core_tests_pigeontest::ErrorOr<std::vector<uint8_t>> EchoUint8List(
       const std::vector<uint8_t>& a_uint8_list) override;
+  core_tests_pigeontest::ErrorOr<flutter::EncodableValue> EchoObject(
+      const flutter::EncodableValue& an_object) override;
   core_tests_pigeontest::ErrorOr<std::optional<std::string>>
   ExtractNestedNullableString(
       const core_tests_pigeontest::AllNullableTypesWrapper& wrapper) override;
@@ -67,7 +69,8 @@ class TestPlugin : public flutter::Plugin,
   core_tests_pigeontest::ErrorOr<std::optional<std::vector<uint8_t>>>
   EchoNullableUint8List(
       const std::vector<uint8_t>* a_nullable_uint8_list) override;
-
+  core_tests_pigeontest::ErrorOr<std::optional<flutter::EncodableValue>>
+  EchoNullableObject(const flutter::EncodableValue* a_nullable_object) override;
   void NoopAsync(std::function<
                  void(std::optional<core_tests_pigeontest::FlutterError> reply)>
                      result) override;

packages/pigeon/pubspec.yaml

@@ -2,7 +2,7 @@ name: pigeon
 description: Code generator tool to make communication between Flutter and the host platform type-safe and easier.
 repository: https://github.com/flutter/packages/tree/main/packages/pigeon
 issue_tracker: https://github.com/flutter/flutter/issues?q=is%3Aissue+is%3Aopen+label%3Apigeon
-version: 4.2.15 # This must match the version in lib/generator_tools.dart
+version: 4.2.16 # This must match the version in lib/generator_tools.dart
 
 environment:
   sdk: ">=2.12.0 <3.0.0"

packages/pigeon/test/cpp_generator_test.dart

@@ -809,6 +809,12 @@ void main() {
                   baseName: 'ParameterObject',
                   isNullable: true,
                 )),
+            NamedType(
+                name: 'aGenericObject',
+                type: const TypeDeclaration(
+                  baseName: 'Object',
+                  isNullable: true,
+                )),
           ],
           returnType: const TypeDeclaration.voidDeclaration(),
         ),
@@ -834,7 +840,8 @@ void main() {
               'const std::string* a_string, '
               'const flutter::EncodableList* a_list, '
               'const flutter::EncodableMap* a_map, '
-              'const ParameterObject* an_object)'));
+              'const ParameterObject* an_object, '
+              'const flutter::EncodableValue* a_generic_object)'));
     }
     {
       final StringBuffer sink = StringBuffer();
@@ -875,6 +882,12 @@ void main() {
           code,
           contains(
               'const auto* an_object_arg = &(std::any_cast<const ParameterObject&>(std::get<flutter::CustomEncodableValue>(encodable_an_object_arg)));'));
+      // "Object" requires no extraction at all since it has to use
+      // EncodableValue directly.
+      expect(
+          code,
+          contains(
+              'const auto* a_generic_object_arg = &encodable_a_generic_object_arg;'));
     }
   });
 
@@ -927,6 +940,12 @@ void main() {
                   baseName: 'ParameterObject',
                   isNullable: false,
                 )),
+            NamedType(
+                name: 'aGenericObject',
+                type: const TypeDeclaration(
+                  baseName: 'Object',
+                  isNullable: false,
+                )),
           ],
           returnType: const TypeDeclaration.voidDeclaration(),
         ),
@@ -952,7 +971,8 @@ void main() {
               'const std::string& a_string, '
               'const flutter::EncodableList& a_list, '
               'const flutter::EncodableMap& a_map, '
-              'const ParameterObject& an_object)'));
+              'const ParameterObject& an_object, '
+              'const flutter::EncodableValue& a_generic_object)'));
     }
     {
       final StringBuffer sink = StringBuffer();
@@ -988,6 +1008,12 @@ void main() {
           code,
           contains(
               'const auto& an_object_arg = std::any_cast<const ParameterObject&>(std::get<flutter::CustomEncodableValue>(encodable_an_object_arg));'));
+      // "Object" requires no extraction at all since it has to use
+      // EncodableValue directly.
+      expect(
+          code,
+          contains(
+              'const auto& a_generic_object_arg = encodable_a_generic_object_arg;'));
     }
   });