Add Support for Threadsafe and NotThreadSafe annotations

Samples/JavaKitSampleApp/Sources/JavaKitExample/JavaKitExample.swift

@@ -76,6 +76,9 @@ extension HelloSwift: HelloSwiftNativeMethods {
       print("Caught Java error: \(error)")
     }
 
+    // Make sure that the thread safe class is sendable
+    let threadSafe: Sendable = ThreadSafeHelperClass(environment: javaEnvironment)
+
     return i * j
   }
 

Samples/JavaKitSampleApp/Sources/JavaKitExample/com/example/swift/ThreadSafe.java

@@ -0,0 +1,22 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2024 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 com.example.swift;
+
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+
+@Retention(RetentionPolicy.RUNTIME)
+public @interface ThreadSafe {
+}

Samples/JavaKitSampleApp/Sources/JavaKitExample/com/example/swift/ThreadSafeHelperClass.java

@@ -0,0 +1,6 @@
+package com.example.swift;
+
+@ThreadSafe
+public class ThreadSafeHelperClass {
+    public ThreadSafeHelperClass() { }
+}

Samples/JavaKitSampleApp/Sources/JavaKitExample/swift-java.config

@@ -2,6 +2,7 @@
   "classes" : {
     "com.example.swift.HelloSwift" : "HelloSwift",
     "com.example.swift.HelloSubclass" : "HelloSubclass",
-    "com.example.swift.JavaKitSampleMain" : "JavaKitSampleMain"
+    "com.example.swift.JavaKitSampleMain" : "JavaKitSampleMain",
+    "com.example.swift.ThreadSafeHelperClass" : "ThreadSafeHelperClass"
   }
 }

Sources/Java2SwiftLib/JavaClassTranslator.swift

@@ -52,6 +52,9 @@ struct JavaClassTranslator {
   /// The Swift names of the interfaces that this class implements.
   let swiftInterfaces: [String]
 
+  /// The annotations of the Java class
+  let annotations: [Annotation]
+
   /// The (instance) fields of the Java class.
   var fields: [Field] = []
 
@@ -164,6 +167,8 @@ struct JavaClassTranslator {
       }
     }
 
+    self.annotations = javaClass.getAnnotations().compactMap(\.self)
+
     // Collect all of the class members that we will need to translate.
     // TODO: Switch over to "declared" versions of these whenever we don't need
     // to see inherited members.
@@ -274,6 +279,7 @@ extension JavaClassTranslator {
     if let nativeMethodsProtocol = renderNativeMethodsProtocol() {
       allDecls.append(nativeMethodsProtocol)
     }
+    allDecls.append(contentsOf: renderAnnotationExtensions())
     return allDecls
   }
 
@@ -483,6 +489,30 @@ extension JavaClassTranslator {
     return protocolDecl.formatted(using: translator.format).cast(DeclSyntax.self)
   }
 
+  func renderAnnotationExtensions() -> [DeclSyntax] {
+    var extensions: [DeclSyntax] = []
+
+    for annotation in annotations {
+      let annotationName = annotation.annotationType().getName().splitSwiftTypeName().name
+      if annotationName == "ThreadSafe" || annotationName == "Immutable" { // If we are threadsafe, mark as unchecked Sendable
+        extensions.append(
+          """
+          extension \(raw: swiftTypeName): @unchecked Swift.Sendable { }
+          """
+        )
+      } else if annotationName == "NotThreadSafe" { // If we are _not_ threadsafe, mark sendable unavailable
+        extensions.append(
+          """
+          @available(unavailable, *)
+          extension \(raw: swiftTypeName): Swift.Sendable { }
+          """
+        )
+      }
+    }
+
+    return extensions
+  }
+
   /// Render the given Java constructor as a Swift initializer.
   package func renderConstructor(
     _ javaConstructor: Constructor<some AnyJavaObject>

Sources/JavaKitReflection/JavaClass+Reflection.swift

@@ -43,4 +43,7 @@ extension JavaClass {
 
   @JavaMethod
   public func getGenericInterfaces() -> [Type?]
+
+  @JavaMethod
+  public func getAnnotations() -> [Annotation?]
 }