[jnigen] Kotlin interfaces with suspend methods

pkgs/jni/lib/_internal.dart

@@ -52,7 +52,13 @@ export 'src/jni.dart' show ProtectedJniExtensions;
 export 'src/jobject.dart' show $JObject$NullableType$, $JObject$Type$;
 export 'src/jreference.dart';
 export 'src/kotlin.dart'
-    show coroutineSingletonsClass, failureExceptionField, result$FailureClass;
+    show
+        KotlinContinuation,
+        coroutineSingletonsClass,
+        failureExceptionField,
+        result$Class,
+        result$FailureClass,
+        resultValueField;
 export 'src/lang/jboolean.dart' show $JBoolean$NullableType$, $JBoolean$Type$;
 export 'src/lang/jbyte.dart' show $JByte$NullableType$, $JByte$Type$;
 export 'src/lang/jcharacter.dart'

pkgs/jni/lib/src/kotlin.dart

@@ -4,6 +4,8 @@
 
 import 'package:meta/meta.dart' show internal;
 
+import 'jni.dart';
+import 'jobject.dart';
 import 'types.dart';
 
 @internal
@@ -16,3 +18,44 @@ final result$FailureClass = JClass.forName(r'kotlin/Result$Failure');
 @internal
 final failureExceptionField =
     result$FailureClass.instanceFieldId('exception', 'Ljava/lang/Throwable;');
+
+@internal
+final result$Class = JClass.forName(r'kotlin/Result');
+
+@internal
+final resultValueField =
+    result$Class.instanceFieldId('value', 'Ljava/lang/Object;');
+
+final _coroutineIntrinsicsClass =
+    JClass.forName('kotlin/coroutines/intrinsics/IntrinsicsKt');
+final _coroutineSuspended = _coroutineIntrinsicsClass.staticMethodId(
+        'getCOROUTINE_SUSPENDED', '()Ljava/lang/Object;')(
+    _coroutineIntrinsicsClass, const $JObject$Type$(), []);
+
+@internal
+class KotlinContinuation extends JObject {
+  KotlinContinuation.fromReference(
+    super.reference,
+  ) : super.fromReference();
+
+  static final _class = JClass.forName(r'kotlin/coroutines/Continuation');
+
+  static final _resumeWithId =
+      _class.instanceMethodId(r'resumeWith', r'(Ljava/lang/Object;)V');
+  void resumeWith(JObject? result) {
+    _resumeWithId(this, const jvoidType(), [result]);
+  }
+
+  static final _result$FailureConstructor =
+      result$FailureClass.constructorId(r'(Ljava/lang/Throwable;)V');
+  void resumeWithException(Object dartException, StackTrace stackTrace) {
+    resumeWith(_result$FailureConstructor(result$FailureClass, JObject.type, [
+      ProtectedJniExtensions.newDartException('$dartException\n$stackTrace'),
+    ]));
+  }
+
+  JObject resumeWithFuture(Future<JObject?> future) {
+    future.then(resumeWith, onError: resumeWithException);
+    return _coroutineSuspended;
+  }
+}

pkgs/jni/lib/src/plugin/generated_plugin.dart

@@ -1,4 +1,4 @@
-// AUTO GENERATED BY JNIGEN 0.15.0. DO NOT EDIT!
+// AUTO GENERATED BY JNIGEN 0.15.1. DO NOT EDIT!
 
 // Copyright (c) 2025, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a

pkgs/jnigen/CHANGELOG.md

@@ -1,6 +1,8 @@
 ## 0.15.1-wip
 
 - Add docs about debugging.
+- Add support for Kotlin interfaces with suspend functions. These can now be
+  implemented using Dart functions that return a `Future`.
 
 ## 0.15.0
 

pkgs/jnigen/lib/src/bindings/dart_generator.dart

@@ -81,6 +81,22 @@ extension on DeclaredType {
   }
 }
 
+extension on Method {
+  bool get isSuspendFun => asyncReturnType != null;
+
+  String returnTypeMaybeAsync(_TypeGenerator generator) => isSuspendFun
+      ? '$_core.Future<${asyncReturnType!.accept(generator)}>'
+      : returnType.accept(generator);
+
+  List<Param> get paramsMaybeAsync {
+    final p = params.toList();
+    if (isSuspendFun) {
+      p.removeLast();
+    }
+    return p;
+  }
+}
+
 String _newLine({int depth = 0}) {
   return '\n${'  ' * depth}';
 }
@@ -1337,10 +1353,6 @@ ${modifier}final _$name = $_protectedExtension
 ''');
   }
 
-  bool isSuspendFun(Method node) {
-    return node.asyncReturnType != null;
-  }
-
   String constructor(Method node) {
     final name = node.finalName;
     final params = [
@@ -1447,10 +1459,7 @@ ${modifier}final _$name = $_protectedExtension
     }
 
     final name = node.finalName;
-    final returnType = isSuspendFun(node)
-        ? '$_core.Future<'
-            '${node.asyncReturnType!.accept(_TypeGenerator(resolver))}>'
-        : node.returnType.accept(_TypeGenerator(resolver));
+    final returnType = node.returnTypeMaybeAsync(_TypeGenerator(resolver));
     final ifStatic = node.isStatic && !isTopLevel ? 'static ' : '';
     final defArgs = node.params.accept(_ParamDef(resolver)).toList();
     final typeClassDef = node.typeParams
@@ -1465,14 +1474,14 @@ ${modifier}final _$name = $_protectedExtension
         .accept(const _TypeParamDef())
         .join(', ')
         .encloseIfNotEmpty('<', '>');
-    if (isSuspendFun(node)) {
+    if (node.isSuspendFun) {
       defArgs.removeLast();
       localReferences.removeLast();
     }
     final params = defArgs.delimited(', ');
     s.write('  $ifStatic$returnType $name$typeParamsDef($params$typeClassDef)');
     final callExpr = methodCall(node);
-    if (isSuspendFun(node)) {
+    if (node.isSuspendFun) {
       final returningType =
           node.asyncReturnType!.accept(_TypeGenerator(resolver));
       final returningTypeClass =
@@ -1486,13 +1495,15 @@ ${modifier}final _$name = $_protectedExtension
     ${localReferences.join(_newLine(depth: 2))}
     final \$r = $callExpr;
     _\$$continuation.release();
-    final $_jObject${isNullable ? '?' : ''} \$o;
+    $_jObject${isNullable ? '?' : ''} \$o;
     if (${isNullable ? '\$r != null && ' : ''}\$r.isInstanceOf($_jni.coroutineSingletonsClass)) {
       \$r.release();
       final \$a = await \$p.first;
       \$o = ${isNullable ? '\$a == 0 ? null :' : ''}$_jObject.fromReference(
           $_jGlobalReference($_jPointer.fromAddress(\$a)));
-      if (${isNullable ? '\$o != null && ' : ''}\$o.isInstanceOf($_jni.result\$FailureClass)) {
+      if (${isNullable ? '\$o != null && ' : ''}\$o.isInstanceOf($_jni.result\$Class)) {
+        \$o = $_jni.resultValueField.get(\$o, const ${_jObjectTypePrefix}Type\$());
+      } else if (${isNullable ? '\$o != null && ' : ''}\$o.isInstanceOf($_jni.result\$FailureClass)) {
         final \$e =
             $_jni.failureExceptionField.get(\$o, const ${_jObjectTypePrefix}Type\$());
         \$o.release();
@@ -1862,11 +1873,10 @@ class _ConcreteImplClosureDef extends Visitor<Method, void> {
 
   @override
   void visit(Method node) {
-    final returnType = node.returnType.accept(
-      _TypeGenerator(resolver, forInterfaceImplementation: true),
-    );
+    final returnType = node.returnTypeMaybeAsync(
+        _TypeGenerator(resolver, forInterfaceImplementation: true));
     final name = node.finalName;
-    final args = node.params
+    final args = node.paramsMaybeAsync
         .accept(_ParamDef(resolver, methodGenericErasure: true))
         .join(', ');
     s.writeln('  final $returnType Function($args) _$name;');
@@ -1885,11 +1895,11 @@ class _AbstractImplFactoryArg extends Visitor<Method, String> {
 
   @override
   String visit(Method node) {
-    final returnType = node.returnType.accept(
+    final returnType = node.returnTypeMaybeAsync(
       _TypeGenerator(resolver, forInterfaceImplementation: true),
     );
     final name = node.finalName;
-    final args = node.params
+    final args = node.paramsMaybeAsync
         .accept(_ParamDef(resolver, methodGenericErasure: true))
         .join(', ');
     final functionArg = 'required $returnType Function($args) $name,';
@@ -1909,11 +1919,11 @@ class _ConcreteImplClosureCtorArg extends Visitor<Method, String> {
 
   @override
   String visit(Method node) {
-    final returnType = node.returnType.accept(
+    final returnType = node.returnTypeMaybeAsync(
       _TypeGenerator(resolver, forInterfaceImplementation: true),
     );
     final name = node.finalName;
-    final args = node.params
+    final args = node.paramsMaybeAsync
         .accept(_ParamDef(resolver, methodGenericErasure: true))
         .join(', ');
     final functionArg = 'required $returnType Function($args) $name,';
@@ -1940,11 +1950,21 @@ class _ConcreteImplMethod extends Visitor<Method, void> {
     final argsDef = node.params
         .accept(_ParamDef(resolver, methodGenericErasure: true))
         .join(', ');
-    final argsCall = node.params.map((param) => param.finalName).join(', ');
-    s.write('''
+    final argsCall =
+        node.paramsMaybeAsync.map((param) => param.finalName).join(', ');
+    if (node.isSuspendFun) {
+      final contArg = node.params.last.finalName;
+      s.write('''
+  $returnType $name($argsDef) {
+    return $_jni.KotlinContinuation.fromReference($contArg.reference)
+        .resumeWithFuture(_$name($argsCall));
+  }''');
+    } else {
+      s.write('''
   $returnType $name($argsDef) {
     return _$name($argsCall);
   }''');
+    }
   }
 }