[jextract] add support for strings in JNI

Sources/JExtractSwiftLib/JNI/JNISwift2JavaGenerator.swift

@@ -134,8 +134,8 @@ extension JNISwift2JavaGenerator {
       """
     ) { printer in
       let downcallParameters = zip(decl.functionSignature.parameters, translatedParameters).map { originalParam, translatedParam in
-        let label = originalParam.argumentLabel ?? originalParam.parameterName ?? ""
-        return "\(label)\(!label.isEmpty ? ": " : "")\(originalParam.type)(fromJNI: \(translatedParam.0), in: environment!)"
+        let label = originalParam.argumentLabel.map { "\($0): "} ?? ""
+        return "\(label)\(originalParam.type)(fromJNI: \(translatedParam.0), in: environment!)"
       }
       let functionDowncall = "\(swiftModuleName).\(decl.name)(\(downcallParameters.joined(separator: ", ")))"
 
@@ -247,7 +247,8 @@ extension SwiftStandardLibraryTypeKind {
     case .float: .float
     case .double: .double
     case .void: .void
-    case .uint, .uint8, .uint32, .uint64, .unsafeRawPointer, .unsafeMutableRawPointer, .unsafePointer, .unsafeMutablePointer, .unsafeBufferPointer, .unsafeMutableBufferPointer, .string: nil
+    case .string: .javaLangString
+    case .uint, .uint8, .uint32, .uint64, .unsafeRawPointer, .unsafeMutableRawPointer, .unsafePointer, .unsafeMutablePointer, .unsafeBufferPointer, .unsafeMutableBufferPointer: nil
     }
   }
 }

Tests/JExtractSwiftTests/JNI/JNIModuleTests.swift

@@ -23,6 +23,10 @@ struct JNIModuleTests {
     public func otherPrimitives(b: Bool, f: Float, d: Double)
   """
 
+  let globalMethodWithString = """
+    public func copy(_ string: String) -> String
+  """
+
   @Test
   func generatesModuleJavaClass() throws {
     let input = "public func helloWorld()"
@@ -107,4 +111,43 @@ struct JNIModuleTests {
       ]
     )
   }
+
+  @Test
+  func globalMethodWithString_javaBindings() throws {
+    try assertOutput(
+      input: globalMethodWithString,
+      .jni,
+      .java,
+      expectedChunks: [
+        """
+        /**
+          * Downcall to Swift:
+          * {@snippet lang=swift :
+          * public func copy(_ string: String) -> String
+          * }
+          */
+        public static native java.lang.String copy(java.lang.String string);
+        """,
+      ]
+    )
+  }
+
+  @Test
+  func globalMethodWithString_swiftThunks() throws {
+    try assertOutput(
+      input: globalMethodWithString,
+      .jni,
+      .swift,
+      detectChunkByInitialLines: 1,
+      expectedChunks: [
+          """
+          @_cdecl("Java_com_example_swift_SwiftModule_copy")
+          func swiftjava_SwiftModule_copy__(environment: UnsafeMutablePointer<JNIEnv?>!, thisClass: jclass, string: jstring?) -> jstring? {
+            let result = SwiftModule.copy(String(fromJNI: string, in: environment!))
+            return result.getJNIValue(in: environment)
+          }
+          """,
+      ]
+    )
+  }
 }