jextract/jni: initial support for variadic type

Samples/SwiftJavaExtractJNISampleApp/Sources/MySwiftLibrary/VariadicGenericType.swift

@@ -0,0 +1,35 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2026 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
+//
+//===----------------------------------------------------------------------===//
+
+public struct VariadicBox<each T> {
+  public var values: (repeat each T)
+  public init(values: repeat each T) {
+    self.values = (repeat each values)
+  }
+
+  public static var count: Int {
+    ComputeParameterPackLength.count(ofPack: (repeat each T).self)
+  }
+}
+
+public typealias IntStringBoolBox = VariadicBox<Int, String, Bool>
+
+private enum ComputeParameterPackLength {
+  enum BoolConverter<T> {
+    typealias Bool = Swift.Bool
+  }
+  static func count<each T>(ofPack t: (repeat each T).Type) -> Int {
+    MemoryLayout<(repeat BoolConverter<each T>.Bool)>.size / MemoryLayout<Bool>.stride
+  }
+}

Samples/SwiftJavaExtractJNISampleApp/src/test/java/com/example/swift/VariadicGenericTypeTest.java

@@ -0,0 +1,26 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2026 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 org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+public class VariadicGenericTypeTest {
+    @Test
+    void callSpecializedStaticMethod() {
+        assertEquals(3, IntStringBoolBox.getCount());
+    }
+}

Sources/JExtractSwiftLib/JNI/JNISwift2JavaGenerator+SwiftThunkPrinting.swift

@@ -821,15 +821,15 @@ extension JNISwift2JavaGenerator {
       if type.genericParameterNames.isEmpty {
         type.effectiveSwiftTypeName
       } else {
-        "\(type.baseTypeName)<\(type.genericParameterNames.joined(separator: ", "))>"
+        "\(type.baseTypeName)<\(type.swiftNominal.genericParameters.map(\.packExpansionName).joined(separator: ", "))>"
       }
     let parentProtocol = isEffectivelyGeneric ? "JextractedGenericTypeBridge" : "JextractedTypeBridge"
 
     let bridgeDeclaration =
       if let bridgeWhereClause {
-        "enum \(bridgeName)\(bridgeGenericClause): \(parentProtocol) \(bridgeWhereClause)"
+        "struct \(bridgeName)\(bridgeGenericClause): \(parentProtocol) \(bridgeWhereClause)"
       } else {
-        "enum \(bridgeName)\(bridgeGenericClause): \(parentProtocol)"
+        "struct \(bridgeName)\(bridgeGenericClause): \(parentProtocol)"
       }
 
     printer.printBraceBlock(bridgeDeclaration) { printer in

Sources/JExtractSwiftLib/SwiftTypes/SwiftNominalTypeDeclaration.swift

@@ -205,6 +205,26 @@ package class SwiftGenericParameterDeclaration: SwiftTypeDeclaration {
     self.syntax = node
     super.init(sourceFilePath: sourceFilePath, moduleName: moduleName, name: node.name.text)
   }
+
+  var hasEach: Bool {
+    syntax.specifier?.tokenKind == .keyword(.each)
+  }
+
+  var packReferenceName: String {
+    if hasEach {
+      "each \(name)"
+    } else {
+      name
+    }
+  }
+
+  var packExpansionName: String {
+    if hasEach {
+      "repeat each \(name)"
+    } else {
+      name
+    }
+  }
 }
 
 /// A plain typealias will resolve as the right hand type in generated code.

Sources/JExtractSwiftLib/SwiftTypes/SwiftType.swift

@@ -156,7 +156,7 @@ extension SwiftType: CustomStringConvertible {
   var description: String {
     switch self {
     case .nominal(let nominal): return nominal.description
-    case .genericParameter(let genericParam): return genericParam.name
+    case .genericParameter(let genericParam): return genericParam.packExpansionName
     case .function(let functionType): return functionType.description
     case .metatype(let instanceType):
       var instanceTypeStr = instanceType.description

Sources/SwiftJavaDocumentation/Documentation.docc/SupportedFeatures.md

@@ -88,7 +88,7 @@ SwiftJava's `swift-java jextract` tool automates generating Java bindings from S
 | Unsigned primitive types: `UInt`, `UInt8`, `UInt16`, `UInt32`, `UInt64`              | ✅ *      | ✅ * |
 | String (with copying data)                                                           | ✅        | ✅   |
 | Variadic parameters: `T...`                                                          | ❌        | ❌   |
-| Parametrer packs / Variadic generics                                                 | ❌        | ❌   |
+| Parametrer packs / Variadic generics                                                 | ❌        | 🟡   |
 | Ownership modifiers: `inout`, `borrowing`, `consuming`                               | ❌        | ❌   |
 | Default parameter values: `func p(name: String = "")`                                | ❌        | ❌   |
 | Operators: `+`, `-`, user defined                                                    | ❌        | ❌   |

Tests/JExtractSwiftTests/JNI/JNIGenericTypeTests.swift

@@ -247,6 +247,39 @@ struct JNIGenericTypeTests {
     )
   }
 
+  @Test
+  func generatesOpenerForVariadicGenericStaticMethod() throws {
+    let input =
+      #"""
+      public struct VariadicBox<each T> {
+        public static func describe() -> String {
+          "\(VariadicBox<repeat each T>.self)"
+        }
+      }
+      """#
+
+    try assertOutput(
+      input: input,
+      .jni,
+      .swift,
+      detectChunkByInitialLines: 2,
+      expectedChunks: [
+        """
+        protocol _SwiftModule_VariadicBox_opener {
+          static func _describe(environment: UnsafeMutablePointer<JNIEnv?>!, thisClass: jclass) -> jstring?
+        }
+        """,
+        #"""
+        extension VariadicBox: _SwiftModule_VariadicBox_opener {
+          static func _describe(environment: UnsafeMutablePointer<JNIEnv?>!, thisClass: jclass) -> jstring? {
+            return VariadicBox<repeat each T>.describe().getJNILocalRefValue(in: environment)
+          }
+        }
+        """#,
+      ]
+    )
+  }
+
   @Test
   func genericValueInEnumCase() throws {
     let input =

Tests/JExtractSwiftTests/JNI/JNIJobjectBridgeTests.swift

@@ -26,7 +26,7 @@ struct JNIJobjectBridgeTests {
         """,
       .jni,
       .swift,
-      detectChunkByInitialLines: 2,
+      detectChunkByInitialLines: 1,
       expectedChunks: [
         """
         private enum _JNI_ReefFish {
@@ -48,7 +48,7 @@ struct JNIJobjectBridgeTests {
           }
         """,
         """
-        enum _JNIBridge_ReefFish: JextractedTypeBridge {
+        struct _JNIBridge_ReefFish: JextractedTypeBridge {
           typealias SwiftType = ReefFish
 
           static var javaClass: jclass {
@@ -82,11 +82,11 @@ struct JNIJobjectBridgeTests {
       detectChunkByInitialLines: 1,
       expectedChunks: [
         """
-        enum _JNIBridge_MyID<T: Hashable, U>: JextractedGenericTypeBridge {
+        struct _JNIBridge_MyID<T: Hashable, U>: JextractedGenericTypeBridge {
           typealias SwiftType = MyID<T, U>
         """,
         """
-        enum _JNIBridge_MyValue<T, O, E>: JextractedGenericTypeBridge where O : Swift.Comparable, E : Swift.Error {
+        struct _JNIBridge_MyValue<T, O, E>: JextractedGenericTypeBridge where O : Swift.Comparable, E : Swift.Error {
           typealias SwiftType = MyValue<T, O, E>
         """,
         """
@@ -95,4 +95,26 @@ struct JNIJobjectBridgeTests {
       ]
     )
   }
+
+  @Test("JNI generates explicit bridges for variadic generic types")
+  func generatesBridgeDeclarationForVariadicGenericType() throws {
+    try assertOutput(
+      input: """
+        public struct VariadicBox<each T> {}
+        public func f() -> [Int: VariadicBox<Int, String>] {}
+        """,
+      .jni,
+      .swift,
+      detectChunkByInitialLines: 1,
+      expectedChunks: [
+        """
+        struct _JNIBridge_VariadicBox<each T>: JextractedGenericTypeBridge {
+          typealias SwiftType = VariadicBox<repeat each T>
+        """,
+        """
+        return SwiftModule.f().dictionaryGetJNIValue(in: environment, keyBridge: JavaBoxableBridge<Int>.self, valueBridge: _JNIBridge_VariadicBox<Int, String>.self)
+        """,
+      ]
+    )
+  }
 }