[pigeon] Remove heap allocation in generated C++ code (flutter#6196)

Please let me know if I goofed anything, this is my first time contributing to Pigeon!

Addresses flutter/flutter#144042

packages/pigeon/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 17.1.1
+
+* Removes heap allocation in generated C++ code.
+
 ## 17.1.0
 
 * [kotlin] Adds `includeErrorClass` to `KotlinOptions`.

packages/pigeon/example/app/README.md

@@ -5,5 +5,6 @@ application, rather than in a plugin.
 
 To update the generated code, run:
 ```sh
-dart run pigeon --input pigeons/messages.dart
+cd ../..
+dart tool/generate.dart
 ```

packages/pigeon/example/app/windows/runner/messages.g.cpp

@@ -141,13 +141,12 @@ const flutter::StandardMessageCodec& ExampleHostApi::GetCodec() {
 void ExampleHostApi::SetUp(flutter::BinaryMessenger* binary_messenger,
                            ExampleHostApi* api) {
   {
-    auto channel = std::make_unique<BasicMessageChannel<>>(
-        binary_messenger,
-        "dev.flutter.pigeon.pigeon_example_package.ExampleHostApi."
-        "getHostLanguage",
-        &GetCodec());
+    BasicMessageChannel<> channel(binary_messenger,
+                                  "dev.flutter.pigeon.pigeon_example_package."
+                                  "ExampleHostApi.getHostLanguage",
+                                  &GetCodec());
     if (api != nullptr) {
-      channel->SetMessageHandler(
+      channel.SetMessageHandler(
           [api](const EncodableValue& message,
                 const flutter::MessageReply<EncodableValue>& reply) {
             try {
@@ -164,16 +163,16 @@ void ExampleHostApi::SetUp(flutter::BinaryMessenger* binary_messenger,
             }
           });
     } else {
-      channel->SetMessageHandler(nullptr);
+      channel.SetMessageHandler(nullptr);
     }
   }
   {
-    auto channel = std::make_unique<BasicMessageChannel<>>(
+    BasicMessageChannel<> channel(
         binary_messenger,
         "dev.flutter.pigeon.pigeon_example_package.ExampleHostApi.add",
         &GetCodec());
     if (api != nullptr) {
-      channel->SetMessageHandler(
+      channel.SetMessageHandler(
           [api](const EncodableValue& message,
                 const flutter::MessageReply<EncodableValue>& reply) {
             try {
@@ -203,16 +202,16 @@ void ExampleHostApi::SetUp(flutter::BinaryMessenger* binary_messenger,
             }
           });
     } else {
-      channel->SetMessageHandler(nullptr);
+      channel.SetMessageHandler(nullptr);
     }
   }
   {
-    auto channel = std::make_unique<BasicMessageChannel<>>(
+    BasicMessageChannel<> channel(
         binary_messenger,
         "dev.flutter.pigeon.pigeon_example_package.ExampleHostApi.sendMessage",
         &GetCodec());
     if (api != nullptr) {
-      channel->SetMessageHandler(
+      channel.SetMessageHandler(
           [api](const EncodableValue& message,
                 const flutter::MessageReply<EncodableValue>& reply) {
             try {
@@ -239,7 +238,7 @@ void ExampleHostApi::SetUp(flutter::BinaryMessenger* binary_messenger,
             }
           });
     } else {
-      channel->SetMessageHandler(nullptr);
+      channel.SetMessageHandler(nullptr);
     }
   }
 }
@@ -273,12 +272,11 @@ void MessageFlutterApi::FlutterMethod(
   const std::string channel_name =
       "dev.flutter.pigeon.pigeon_example_package.MessageFlutterApi."
       "flutterMethod";
-  auto channel = std::make_unique<BasicMessageChannel<>>(
-      binary_messenger_, channel_name, &GetCodec());
+  BasicMessageChannel<> channel(binary_messenger_, channel_name, &GetCodec());
   EncodableValue encoded_api_arguments = EncodableValue(EncodableList{
       a_string_arg ? EncodableValue(*a_string_arg) : EncodableValue(),
   });
-  channel->Send(
+  channel.Send(
       encoded_api_arguments, [channel_name, on_success = std::move(on_success),
                               on_error = std::move(on_error)](
                                  const uint8_t* reply, size_t reply_size) {

packages/pigeon/lib/cpp_generator.dart

@@ -871,11 +871,9 @@ class CppSourceGenerator extends StructuredGenerator<CppOptions> {
           scope: api.name,
           returnType: _voidType,
           parameters: parameters, body: () {
-        const String channel = 'channel';
         indent.writeln(
             'const std::string channel_name = "${makeChannelName(api, func, dartPackageName)}";');
-        indent.writeln(
-            'auto channel = std::make_unique<BasicMessageChannel<>>(binary_messenger_, '
+        indent.writeln('BasicMessageChannel<> channel(binary_messenger_, '
             'channel_name, &GetCodec());');
 
         // Convert arguments to EncodableValue versions.
@@ -894,7 +892,7 @@ class CppSourceGenerator extends StructuredGenerator<CppOptions> {
           });
         }
 
-        indent.write('$channel->Send($argumentListVariableName, '
+        indent.write('channel.Send($argumentListVariableName, '
             // ignore: missing_whitespace_between_adjacent_strings
             '[channel_name, on_success = std::move(on_success), on_error = std::move(on_error)]'
             '(const uint8_t* reply, size_t reply_size) ');
@@ -972,12 +970,11 @@ class CppSourceGenerator extends StructuredGenerator<CppOptions> {
         final String channelName =
             makeChannelName(api, method, dartPackageName);
         indent.writeScoped('{', '}', () {
-          indent.writeln(
-              'auto channel = std::make_unique<BasicMessageChannel<>>(binary_messenger, '
+          indent.writeln('BasicMessageChannel<> channel(binary_messenger, '
               '"$channelName", &GetCodec());');
           indent.writeScoped('if (api != nullptr) {', '} else {', () {
             indent.write(
-                'channel->SetMessageHandler([api](const EncodableValue& message, const flutter::MessageReply<EncodableValue>& reply) ');
+                'channel.SetMessageHandler([api](const EncodableValue& message, const flutter::MessageReply<EncodableValue>& reply) ');
             indent.addScoped('{', '});', () {
               indent.writeScoped('try {', '}', () {
                 final List<String> methodArgument = <String>[];
@@ -1054,7 +1051,7 @@ class CppSourceGenerator extends StructuredGenerator<CppOptions> {
             });
           });
           indent.addScoped(null, '}', () {
-            indent.writeln('channel->SetMessageHandler(nullptr);');
+            indent.writeln('channel.SetMessageHandler(nullptr);');
           });
         });
       }

packages/pigeon/lib/generator_tools.dart

@@ -13,7 +13,7 @@ import 'ast.dart';
 /// The current version of pigeon.
 ///
 /// This must match the version in pubspec.yaml.
-const String pigeonVersion = '17.1.0';
+const String pigeonVersion = '17.1.1';
 
 /// Read all the content from [stdin] to a String.
 String readStdin() {

packages/pigeon/platform_tests/test_plugin/example/windows/flutter/CMakeLists.txt

@@ -10,6 +10,11 @@ include(${EPHEMERAL_DIR}/generated_config.cmake)
 # https://github.com/flutter/flutter/issues/57146.
 set(WRAPPER_ROOT "${EPHEMERAL_DIR}/cpp_client_wrapper")
 
+# Set fallback configurations for older versions of the flutter tool.
+if (NOT DEFINED FLUTTER_TARGET_PLATFORM)
+  set(FLUTTER_TARGET_PLATFORM "windows-x64")
+endif()
+
 # === Flutter Library ===
 set(FLUTTER_LIBRARY "${EPHEMERAL_DIR}/flutter_windows.dll")
 
@@ -92,7 +97,7 @@ add_custom_command(
   COMMAND ${CMAKE_COMMAND} -E env
     ${FLUTTER_TOOL_ENVIRONMENT}
     "${FLUTTER_ROOT}/packages/flutter_tools/bin/tool_backend.bat"
-      windows-x64 $<CONFIG>
+      ${FLUTTER_TARGET_PLATFORM} $<CONFIG>
   VERBATIM
 )
 add_custom_target(flutter_assemble DEPENDS