[pigeon] Added basic C++ support

packages/pigeon/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 3.1.0
+
+* [c++] Adds C++ code generator.
+
 ## 3.0.4
 
 * [objc] Simplified some code output, including avoiding Xcode warnings about
@@ -35,8 +39,8 @@
 ## 2.0.2
 
 * Fixes Java crash for nullable nested type.
-
-* ## 2.0.1
+  
+## 2.0.1
 
 * Adds support for TaskQueues for serial background execution.
 

packages/pigeon/CONTRIBUTING.md

@@ -23,6 +23,7 @@ generators with that AST.
 * [java_generator.dart](./lib/java_generator.dart) - The Java code generator.
 * [objc_generator.dart](./lib/objc_generator.dart) - The Objective-C code
   generator (header and source files).
+* [cpp_generator.dart](./lib/cpp_generator.dart) - The C++ code generator.
 * [generator_tools.dart](./lib/generator_tools.dart) - Shared code between generators.
 * [pigeon_cl.dart](./lib/pigeon_cl.dart) - The top-level function executed by
   the command line tool in [bin/][./bin].

packages/pigeon/README.md

@@ -5,8 +5,9 @@ host platform type-safe, easier and faster.
 
 ## Supported Platforms
 
-Currently Pigeon only supports generating Objective-C code for usage on iOS and
-Java code for Android.  The Objective-C code is
+Currently Pigeon supports generating Objective-C code for usage on iOS, Java
+code for Android, and has experimental support for C++ for Windows. The
+Objective-C code is
 [accessible to Swift](https://developer.apple.com/documentation/swift/imported_c_and_objective-c_apis/importing_objective-c_into_swift)
 and the Java code is accessible to Kotlin.
 
@@ -18,32 +19,39 @@ doesn't need to worry about conflicting versions of Pigeon.
 
 ## Usage
 
-### Flutter calling into iOS Steps
+1) Add Pigeon as a `dev_dependency`.
+1) Make a ".dart" file outside of your "lib" directory for defining the
+   communication interface.
+1) Run pigeon on your ".dart" file to generate the required Dart and 
+   host-language code: `flutter pub get` then `flutter pub run pigeon` 
+   with suitable arguments (see [example](./example)).
+1) Add the generated Dart code to `./lib` for compilation.
+1) Implement the host-language code and add it to your build (see below).
+1) Call the generated Dart methods.
+
+### Flutter calling into iOS steps
 
-1) Add Pigeon as a dev_dependency.
-1) Make a ".dart" file outside of your "lib" directory for defining the communication interface.
-1) Run pigeon on your ".dart" file to generate the required Dart and Objective-C
-   code: `flutter pub get` then `flutter pub run pigeon` with suitable arguments
-   (see [example](./example)).
-1) Add the generated Dart code to `lib` for compilation.
 1) Add the generated Objective-C code to your Xcode project for compilation
    (e.g. `ios/Runner.xcworkspace` or `.podspec`).
 1) Implement the generated iOS protocol for handling the calls on iOS, set it up
    as the handler for the messages.
-1) Call the generated Dart methods.
 
 ### Flutter calling into Android Steps
 
-1) Add Pigeon as a dev_dependency.
-1) Make a ".dart" file outside of your "lib" directory for defining the communication interface.
-1) Run pigeon on your ".dart" file to generate the required Dart and Java code.
-   `flutter pub get` then `flutter pub run pigeon` with suitable arguments
-   (see [example](./example)).
-1) Add the generated Dart code to `./lib` for compilation.
-1) Add the generated Java code to your `./android/app/src/main/java` directory for compilation.
-1) Implement the generated Java interface for handling the calls on Android, set it up
-   as the handler for the messages.
-1) Call the generated Dart methods.
+1) Add the generated Java code to your `./android/app/src/main/java` directory
+   for compilation.
+1) Implement the generated Java interface for handling the calls on Android, set
+   it up as the handler for the messages.
+
+### Flutter calling into Windows Steps
+
+1) Add the generated C++ code to your `./windows` directory for compilation, and
+   to your `windows/CMakeLists.txt` file.
+1) Implement the generated C++ abstract class for handling the calls on Windows,
+   set it up as the handler for the messages.
+
+**Note:** Windows C++ is experimental while we get more usage and add more
+testing.  Not all features may be supported.
 
 ### Calling into Flutter from the host platform
 
@@ -116,6 +124,16 @@ public interface Api2Host {
 }
 ```
 
+```c++
+// C++
+
+/** Generated class from Pigeon that represents a handler of messages from Flutter.*/
+class Api2Host {
+public:
+    virtual void calculate(Value value, flutter::MessageReply<Value> result) = 0;
+}
+```
+
 ### Null Safety (NNBD)
 
 Pigeon supports generating null-safe code, but it doesn't yet support: