JNI: closures taking optional strings and numbers wrap them as Java optionals

A closure taking `String?` converts the argument with `toJavaOptional()`,
which makes a `JavaOptional<JavaString>`, but the closure's `@JavaInterface`
declared the parameter as `String?`, so the generated Swift didn't compile.
Optional `String`, `Double`, `Int32` and `Int64` parameters now use the types
`toJavaOptional()` returns.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: piercifani

Sources/JExtractSwiftLib/JNI/JNISwift2JavaGenerator+EscapingClosureWrapJava.swift

@@ -93,6 +93,16 @@ extension JNISwift2JavaGenerator {
     if !isResult, let nominal = optionalWrapped(type).flatMap(jextractedNominal) {
       return "JavaOptional<\(nominal.generatedJavaClassMacroName)>?"
     }
+    // Optional strings and numbers cross as what `Optional.toJavaOptional()` makes of them.
+    if !isResult, let wrapped = optionalWrapped(type), case .nominal(let nominal) = wrapped {
+      switch nominal.nominalTypeDecl.knownTypeKind {
+      case .string: return "JavaOptional<JavaString>?"
+      case .double: return "JavaOptionalDouble?"
+      case .int32: return "JavaOptionalInt?"
+      case .int64: return "JavaOptionalLong?"
+      default: break
+      }
+    }
     // Arrays of jextracted values cross as arrays of their Java objects.
     if !isResult, case .nominal(let array) = type, case .array(let element) = array.asKnownType,
       let nominal = jextractedNominal(element)

Tests/JExtractSwiftTests/JNI/JNIEscapingClosureJExtractedTypesTests.swift

@@ -228,4 +228,16 @@ struct JNIEscapingClosureJExtractedTypesTests {
       ]
     )
   }
+
+  @Test
+  func closureTakingOptionalString_usesJavaOptional() throws {
+    try assertOutput(
+      input: "public func onVerify(_ cb: @escaping (String?, Int64?) -> Void) {}",
+      .jni,
+      .swift,
+      expectedChunks: [
+        "public func apply(_ _0: JavaOptional<JavaString>?, _ _1: JavaOptionalLong?)"
+      ]
+    )
+  }
 }