add "future" mode

Author: madsodgaard

Sources/JExtractSwiftLib/JNI/JNISwift2JavaGenerator+JavaTranslation.swift

@@ -496,12 +496,29 @@ extension JNISwift2JavaGenerator {
           annotations: result.annotations,
           outParameters: result.outParameters,
           conversion: .method(.constant("java.util.concurrent.CompletableFuture"), function: "supplyAsync", arguments: [
-            .lambda(body: supplyAsyncBodyConversion)
+            .lambda(body: supplyAsyncBodyConversion),
+            .constant("SwiftAsync.SWIFT_ASYNC_EXECUTOR")
           ])
         )
 
       case .future:
-        fatalError("TODO")
+        let asyncBodyConversion: JavaNativeConversionStep = if result.javaType.isVoid {
+          .aggregate([
+            .print(result.conversion),
+            .null
+          ])
+        } else {
+          result.conversion
+        }
+
+        return TranslatedResult(
+          javaType: .class(package: "java.util.concurrent", name: "Future<\(result.javaType.wrapperClassIfNeeded)>"),
+          annotations: result.annotations,
+          outParameters: result.outParameters,
+          conversion: .method(.constant("SwiftAsync.SWIFT_ASYNC_EXECUTOR"), function: "submit", arguments: [
+            .lambda(body: asyncBodyConversion)
+          ])
+        )
       }
     }
 

Sources/JExtractSwiftLib/JNI/JNISwift2JavaGenerator+NativeTranslation.swift

@@ -521,7 +521,7 @@ extension JNISwift2JavaGenerator {
       mode: JExtractAsyncMode
     ) -> NativeResult {
       switch mode {
-      case .completableFuture:
+      case .completableFuture, .future:
         return NativeResult(
           javaType: result.javaType,
           conversion: .asyncBlocking(
@@ -531,9 +531,6 @@ extension JNISwift2JavaGenerator {
           ),
           outParameters: result.outParameters
         )
-
-      case .future:
-        fatalError("TODO")
       }
     }
   }

Sources/SwiftJavaTool/Commands/JExtractCommand.swift

@@ -78,6 +78,9 @@ extension SwiftJava {
             """
     )
     var dependsOn: [String] = []
+
+    @Option(help: "The mode to use for extracting asynchronous Swift code. By default async methods are extracted as Java functions returning CompletableFuture.")
+    var asyncMode: JExtractAsyncMode = .default
   }
 }
 
@@ -98,6 +101,7 @@ extension SwiftJava.JExtractCommand {
     config.unsignedNumbersMode = unsignedNumbers
     config.minimumInputAccessLevelMode = minimumInputAccessLevel
     config.memoryManagementMode = memoryManagementMode
+    config.asyncMode = asyncMode
 
     try checkModeCompatibility()
 
@@ -162,3 +166,4 @@ extension JExtractGenerationMode: ExpressibleByArgument {}
 extension JExtractUnsignedIntegerMode: ExpressibleByArgument {}
 extension JExtractMinimumAccessLevelMode: ExpressibleByArgument {}
 extension JExtractMemoryManagementMode: ExpressibleByArgument {}
+extension JExtractAsyncMode: ExpressibleByArgument {}

SwiftKitCore/src/main/java/org/swift/swiftkit/core/SwiftAsync.java

@@ -0,0 +1,22 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2025 Apple Inc. and the Swift.org project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+// See CONTRIBUTORS.txt for the list of Swift.org project authors
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+
+package org.swift.swiftkit.core;
+
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+
+public final class SwiftAsync {
+    public static final ExecutorService SWIFT_ASYNC_EXECUTOR = Executors.newCachedThreadPool();
+}