[pigeon] Kotlin implementation for ProxyApis (#6371)

Kotlin portion of flutter/flutter#134777

packages/pigeon/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 22.2.0
+
+* [kotlin] Adds implementation for `@ProxyApi`.
+
 ## 22.1.0
 
 * Allows generation of classes that aren't referenced in an API.

packages/pigeon/example/app/android/app/src/main/kotlin/dev/flutter/pigeon_example_app/Messages.g.kt

@@ -84,7 +84,7 @@ data class MessageData(
   }
 }
 
-private object MessagesPigeonCodec : StandardMessageCodec() {
+private open class MessagesPigeonCodec : StandardMessageCodec() {
   override fun readValueOfType(type: Byte, buffer: ByteBuffer): Any? {
     return when (type) {
       129.toByte() -> {
@@ -122,7 +122,7 @@ interface ExampleHostApi {
 
   companion object {
     /** The codec used by ExampleHostApi. */
-    val codec: MessageCodec<Any?> by lazy { MessagesPigeonCodec }
+    val codec: MessageCodec<Any?> by lazy { MessagesPigeonCodec() }
     /** Sets up an instance of `ExampleHostApi` to handle messages through the `binaryMessenger`. */
     @JvmOverloads
     fun setUp(
@@ -209,7 +209,7 @@ class MessageFlutterApi(
 ) {
   companion object {
     /** The codec used by MessageFlutterApi. */
-    val codec: MessageCodec<Any?> by lazy { MessagesPigeonCodec }
+    val codec: MessageCodec<Any?> by lazy { MessagesPigeonCodec() }
   }
 
   fun flutterMethod(aStringArg: String?, callback: (Result<String>) -> Unit) {

packages/pigeon/lib/ast.dart

@@ -4,7 +4,9 @@
 
 import 'package:collection/collection.dart' show ListEquality;
 import 'package:meta/meta.dart';
+
 import 'generator_tools.dart';
+import 'kotlin_generator.dart' show KotlinProxyApiOptions;
 import 'pigeon_lib.dart';
 
 typedef _ListEquals = bool Function(List<Object?>, List<Object?>);
@@ -140,6 +142,7 @@ class AstProxyApi extends Api {
     required this.fields,
     this.superClass,
     this.interfaces = const <TypeDeclaration>{},
+    this.kotlinOptions,
   });
 
   /// List of constructors inside the API.
@@ -154,6 +157,10 @@ class AstProxyApi extends Api {
   /// Name of the classes this class considers to be implemented.
   Set<TypeDeclaration> interfaces;
 
+  /// Options that control how Kotlin code will be generated for a specific
+  /// ProxyApi.
+  final KotlinProxyApiOptions? kotlinOptions;
+
   /// Methods implemented in the host platform language.
   Iterable<Method> get hostMethods => methods.where(
         (Method method) => method.location == ApiLocation.host,
@@ -253,7 +260,7 @@ class AstProxyApi extends Api {
     }
   }
 
-  /// Whether the api has a method that callbacks to Dart to add a new instance
+  /// Whether the API has a method that callbacks to Dart to add a new instance
   /// to the InstanceManager.
   ///
   /// This is possible as long as no callback methods are required to
@@ -265,6 +272,21 @@ class AstProxyApi extends Api {
         .every((Method method) => !method.isRequired);
   }
 
+  /// Whether the API has any message calls from Dart to host.
+  bool hasAnyHostMessageCalls() =>
+      constructors.isNotEmpty ||
+      attachedFields.isNotEmpty ||
+      hostMethods.isNotEmpty;
+
+  /// Whether the API has any message calls from host to Dart.
+  bool hasAnyFlutterMessageCalls() =>
+      hasCallbackConstructor() || flutterMethods.isNotEmpty;
+
+  /// Whether the host proxy API class will have methods that need to be
+  /// implemented.
+  bool hasMethodsRequiringImplementation() =>
+      hasAnyHostMessageCalls() || unattachedFields.isNotEmpty;
+
   // Recursively search for all the interfaces apis from a list of names of
   // interfaces.
   //

packages/pigeon/lib/dart/templates.dart

@@ -4,6 +4,20 @@
 
 import '../generator_tools.dart';
 
+/// Name for the generated InstanceManager for ProxyApis.
+///
+/// This lowers the chances of variable name collisions with user defined
+/// parameters.
+const String dartInstanceManagerClassName =
+    '${proxyApiClassNamePrefix}InstanceManager';
+
+/// Name for the generated InstanceManager API for ProxyApis.
+///
+/// This lowers the chances of variable name collisions with user defined
+/// parameters.
+const String dartInstanceManagerApiClassName =
+    '_${classNamePrefix}InstanceManagerApi';
+
 /// Creates the `InstanceManager` with the passed string values.
 String instanceManagerTemplate({
   required Iterable<String> allProxyApiNames,
@@ -30,9 +44,9 @@ String instanceManagerTemplate({
 /// is added as a weak reference with the same identifier. This prevents a
 /// scenario where the weak referenced instance was released and then later
 /// returned by the host platform.
-class $instanceManagerClassName {
-  /// Constructs a [$instanceManagerClassName].
-  $instanceManagerClassName({required void Function(int) onWeakReferenceRemoved}) {
+class $dartInstanceManagerClassName {
+  /// Constructs a [$dartInstanceManagerClassName].
+  $dartInstanceManagerClassName({required void Function(int) onWeakReferenceRemoved}) {
     this.onWeakReferenceRemoved = (int identifier) {
       _weakInstances.remove(identifier);
       onWeakReferenceRemoved(identifier);
@@ -46,12 +60,12 @@ class $instanceManagerClassName {
   // 0 <= n < 2^16.
   static const int _maxDartCreatedIdentifier = 65536;
 
-  /// The default [$instanceManagerClassName] used by ProxyApis.
+  /// The default [$dartInstanceManagerClassName] used by ProxyApis.
   ///
   /// On creation, this manager makes a call to clear the native
   /// InstanceManager. This is to prevent identifier conflicts after a host
   /// restart.
-  static final $instanceManagerClassName instance = _initInstance();
+  static final $dartInstanceManagerClassName instance = _initInstance();
 
   // Expando is used because it doesn't prevent its keys from becoming
   // inaccessible. This allows the manager to efficiently retrieve an identifier
@@ -72,17 +86,17 @@ class $instanceManagerClassName {
   /// or becomes inaccessible.
   late final void Function(int) onWeakReferenceRemoved;
 
-  static $instanceManagerClassName _initInstance() {
+  static $dartInstanceManagerClassName _initInstance() {
     WidgetsFlutterBinding.ensureInitialized();
-    final _${instanceManagerClassName}Api api = _${instanceManagerClassName}Api();
-    // Clears the native `$instanceManagerClassName` on the initial use of the Dart one.
+    final $dartInstanceManagerApiClassName api = $dartInstanceManagerApiClassName();
+    // Clears the native `$dartInstanceManagerClassName` on the initial use of the Dart one.
     api.clear();
-    final $instanceManagerClassName instanceManager = $instanceManagerClassName(
+    final $dartInstanceManagerClassName instanceManager = $dartInstanceManagerClassName(
       onWeakReferenceRemoved: (int identifier) {
         api.removeStrongReference(identifier);
       },
     );
-    _${instanceManagerClassName}Api.setUpMessageHandlers(instanceManager: instanceManager);
+    $dartInstanceManagerApiClassName.setUpMessageHandlers(instanceManager: instanceManager);
     ${apiHandlerSetUps.join('\n\t\t')}
     return instanceManager;
   }
@@ -229,9 +243,9 @@ abstract class $proxyApiBaseClassName {
   /// Construct a [$proxyApiBaseClassName].
   $proxyApiBaseClassName({
     this.$_proxyApiBaseClassMessengerVarName,
-    $instanceManagerClassName? $_proxyApiBaseClassInstanceManagerVarName,
+    $dartInstanceManagerClassName? $_proxyApiBaseClassInstanceManagerVarName,
   }) : $_proxyApiBaseClassInstanceManagerVarName =
-            $_proxyApiBaseClassInstanceManagerVarName ?? $instanceManagerClassName.instance;
+            $_proxyApiBaseClassInstanceManagerVarName ?? $dartInstanceManagerClassName.instance;
 
   /// Sends and receives binary data across the Flutter platform barrier.
   ///
@@ -242,12 +256,12 @@ abstract class $proxyApiBaseClassName {
 
   /// Maintains instances stored to communicate with native language objects.
   @protected
-  final $instanceManagerClassName $_proxyApiBaseClassInstanceManagerVarName;
+  final $dartInstanceManagerClassName $_proxyApiBaseClassInstanceManagerVarName;
 
   /// Instantiates and returns a functionally identical object to oneself.
   ///
   /// Outside of tests, this method should only ever be called by
-  /// [$instanceManagerClassName].
+  /// [$dartInstanceManagerClassName].
   ///
   /// Subclasses should always override their parent's implementation of this
   /// method.
@@ -264,11 +278,11 @@ abstract class $proxyApiBaseClassName {
 const String proxyApiBaseCodec = '''
 class $_proxyApiCodecName extends _PigeonCodec {
  const $_proxyApiCodecName(this.instanceManager);
- final $instanceManagerClassName instanceManager;
+ final $dartInstanceManagerClassName instanceManager;
  @override
  void writeValue(WriteBuffer buffer, Object? value) {
    if (value is $proxyApiBaseClassName) {
-     buffer.putUint8(128);
+     buffer.putUint8($proxyApiCodecInstanceManagerKey);
      writeValue(buffer, instanceManager.getIdentifier(value));
    } else {
      super.writeValue(buffer, value);
@@ -277,7 +291,7 @@ class $_proxyApiCodecName extends _PigeonCodec {
  @override
  Object? readValueOfType(int type, ReadBuffer buffer) {
    switch (type) {
-     case 128:
+     case $proxyApiCodecInstanceManagerKey:
        return instanceManager
            .getInstanceWithWeakReference(readValue(buffer)! as int);
      default: