[jextract/jni] Add support for importing nested types (#429)

Author: madsodgaard

Samples/SwiftJavaExtractJNISampleApp/Sources/MySwiftLibrary/NestedTypes.swift

@@ -0,0 +1,47 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+import SwiftJava
+
+public class A {
+  public init() {}
+  
+  public class B {
+    public init() {}
+
+    public struct C {
+      public init() {}
+
+      public func g(a: A, b: B, bbc: BB.C) {}
+    }
+  }
+
+  public class BB {
+    public init() {}
+
+    public struct C {
+      public init() {}
+    }
+  }
+
+  public func f(a: A, b: A.B, c: A.B.C, bb: BB, bbc: BB.C) {}
+}
+
+public enum NestedEnum {
+  case one(OneStruct)
+
+  public struct OneStruct {
+    public init() {}
+  }
+}

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

@@ -0,0 +1,45 @@
+//===----------------------------------------------------------------------===//
+//
+// 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 org.junit.jupiter.api.Test;
+import org.swift.swiftkit.core.SwiftArena;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+public class NestedTypesTest {
+    @Test
+    void testClassesAndStructs() {
+        try (var arena = SwiftArena.ofConfined()) {
+            var a = A.init(arena);
+            var b = A.B.init(arena);
+            var c = A.B.C.init(arena);
+            var bb = A.BB.init(arena);
+            var abbc = A.BB.C.init(arena);
+
+            a.f(a, b, c, bb, abbc);
+            c.g(a, b, abbc);
+        }
+    }
+
+    @Test
+    void testStructInEnum() {
+        try (var arena = SwiftArena.ofConfined()) {
+            var obj = NestedEnum.one(NestedEnum.OneStruct.init(arena), arena);
+            var one = obj.getAsOne(arena);
+            assertTrue(one.isPresent());
+        }
+    }
+}

Sources/JExtractSwiftLib/ImportedDecls.swift

@@ -41,12 +41,14 @@ package final class ImportedNominalType: ImportedDecl {
   package var variables: [ImportedFunc] = []
   package var cases: [ImportedEnumCase] = []
   var inheritedTypes: [SwiftType]
+  package var parent: SwiftNominalTypeDeclaration?
 
   init(swiftNominal: SwiftNominalTypeDeclaration, lookupContext: SwiftTypeLookupContext) throws {
     self.swiftNominal = swiftNominal
     self.inheritedTypes = swiftNominal.inheritanceTypes?.compactMap {
       try? SwiftType($0.type, lookupContext: lookupContext)
     } ?? []
+    self.parent = swiftNominal.parent
   }
 
   var swiftType: SwiftType {

Sources/JExtractSwiftLib/JNI/JNICaching.swift

@@ -14,15 +14,15 @@
 
 enum JNICaching {
   static func cacheName(for type: ImportedNominalType) -> String {
-    cacheName(for: type.swiftNominal.name)
+    cacheName(for: type.swiftNominal.qualifiedName)
   }
 
   static func cacheName(for type: SwiftNominalType) -> String {
-    cacheName(for: type.nominalTypeDecl.name)
+    cacheName(for: type.nominalTypeDecl.qualifiedName)
   }
 
-  private static func cacheName(for name: String) -> String {
-    "_JNI_\(name)"
+  private static func cacheName(for qualifiedName: String) -> String {
+    "_JNI_\(qualifiedName.replacingOccurrences(of: ".", with: "_"))"
   }
 
   static func cacheMemberName(for enumCase: ImportedEnumCase) -> String {

Sources/JExtractSwiftLib/JNI/JNISwift2JavaGenerator+JavaBindingsPrinting.swift

@@ -40,7 +40,9 @@ extension JNISwift2JavaGenerator {
   package func writeExportedJavaSources(_ printer: inout CodePrinter) throws {
     let importedTypes = analysis.importedTypes.sorted(by: { (lhs, rhs) in lhs.key < rhs.key })
 
-    for (_, ty) in importedTypes {
+    // Each parent type goes into its own file
+    // any nested types are printed inside the body as `static class`
+    for (_, ty) in importedTypes.filter({ _, type in type.parent == nil }) {
       let filename = "\(ty.swiftNominal.name).java"
       logger.debug("Printing contents: \(filename)")
       printImportedNominal(&printer, ty)
@@ -145,6 +147,15 @@ extension JNISwift2JavaGenerator {
         """
       )
 
+      let nestedTypes = self.analysis.importedTypes.filter { _, type in
+        type.parent == decl.swiftNominal
+      }
+
+      for nestedType in nestedTypes {
+        printConcreteType(&printer, nestedType.value)
+        printer.println()
+      }
+
       printer.print(
         """
         /**
@@ -255,13 +266,18 @@ extension JNISwift2JavaGenerator {
     if decl.swiftNominal.isSendable {
       printer.print("@ThreadSafe // Sendable")
     }
+    var modifiers = ["public"]
+    if decl.parent != nil {
+      modifiers.append("static")
+    }
+    modifiers.append("final")
     var implements = ["JNISwiftInstance"]
     implements += decl.inheritedTypes
       .compactMap(\.asNominalTypeDeclaration)
       .filter { $0.kind == .protocol }
       .map(\.name)
     let implementsClause = implements.joined(separator: ", ")
-    printer.printBraceBlock("public final class \(decl.swiftNominal.name) implements \(implementsClause)") { printer in
+    printer.printBraceBlock("\(modifiers.joined(separator: " ")) class \(decl.swiftNominal.name) implements \(implementsClause)") { printer in
       body(&printer)
     }
   }

Sources/JExtractSwiftLib/JNI/JNISwift2JavaGenerator+JavaTranslation.swift

@@ -307,9 +307,7 @@ extension JNISwift2JavaGenerator {
       genericParameters: [SwiftGenericParameterDeclaration],
       genericRequirements: [SwiftGenericRequirement]
     ) throws -> [TranslatedParameter] {
-      try parameters.enumerated().map {
-        idx,
-        param in
+      try parameters.enumerated().map { idx, param in
         let parameterName = param.name ?? "arg\(idx)"
         return try translateParameter(
           swiftType: param.type,
@@ -373,7 +371,7 @@ extension JNISwift2JavaGenerator {
 
       switch swiftType {
       case .nominal(let nominalType):
-        let nominalTypeName = nominalType.nominalTypeDecl.name
+        let nominalTypeName = nominalType.nominalTypeDecl.qualifiedName
 
         if let knownType = nominalType.nominalTypeDecl.knownTypeKind {
           switch knownType {

Sources/JExtractSwiftLib/JNI/JNISwift2JavaGenerator+SwiftThunkPrinting.swift

@@ -430,7 +430,7 @@ extension JNISwift2JavaGenerator {
     let cName =
       "Java_"
       + self.javaPackage.replacingOccurrences(of: ".", with: "_")
-      + "_\(parentName.escapedJNIIdentifier)_"
+      + "_\(parentName.replacingOccurrences(of: ".", with: "$").escapedJNIIdentifier)_"
       + javaMethodName.escapedJNIIdentifier
       + "__"
       + jniSignature.escapedJNIIdentifier
@@ -474,7 +474,7 @@ extension JNISwift2JavaGenerator {
     printCDecl(
       &printer,
       javaMethodName: "$typeMetadataAddressDowncall",
-      parentName: type.swiftNominal.name,
+      parentName: type.swiftNominal.qualifiedName,
       parameters: [],
       resultType: .long
     ) { printer in
@@ -493,7 +493,7 @@ extension JNISwift2JavaGenerator {
     printCDecl(
       &printer,
       javaMethodName: "$destroy",
-      parentName: type.swiftNominal.name,
+      parentName: type.swiftNominal.qualifiedName,
       parameters: [
         selfPointerParam
       ],

Sources/JExtractSwiftLib/SwiftTypes/SwiftModuleSymbolTable.swift

@@ -56,4 +56,4 @@ extension SwiftModuleSymbolTable {
     /// Names of modules which are alternative for currently checked module.
     let moduleNames: Set<String>
   }
-}
+}

Sources/JExtractSwiftLib/SwiftTypes/SwiftTypeLookupContext.swift

@@ -119,7 +119,15 @@ class SwiftTypeLookupContext {
 
   /// Create a nominal type declaration instance for the specified syntax node.
   private func nominalTypeDeclaration(for node: NominalTypeDeclSyntaxNode, sourceFilePath: String) throws -> SwiftNominalTypeDeclaration {
-    SwiftNominalTypeDeclaration(
+
+    if let symbolTableDeclaration = self.symbolTable.lookupType(
+      node.name.text,
+      parent: try parentTypeDecl(for: node)
+    ) {
+      return symbolTableDeclaration
+    }
+
+    return SwiftNominalTypeDeclaration(
       sourceFilePath: sourceFilePath,
       moduleName: self.symbolTable.moduleName,
       parent: try parentTypeDecl(for: node),

Sources/SwiftJavaDocumentation/Documentation.docc/SupportedFeatures.md

@@ -86,7 +86,7 @@ SwiftJava's `swift-java jextract` tool automates generating Java bindings from S
 | Subscripts: `subscript()`                                                            | ❌        | ❌   |
 | Equatable                                                                            | ❌        | ❌   |
 | Pointers: `UnsafeRawPointer`, UnsafeBufferPointer (?)                                | 🟡       | ❌   |
-| Nested types: `struct Hello { struct World {} }`                                     | ❌        | ❌   |
+| Nested types: `struct Hello { struct World {} }`                                     | ❌        | ✅   |
 | Inheritance: `class Caplin: Capybara`                                                | ❌        | ❌   |
 | Non-escaping `Void` closures: `func callMe(maybe: () -> ())`                                      | ✅        | ✅   |
 | Non-escaping closures with primitive arguments/results: `func callMe(maybe: (Int) -> (Double))`   | ✅        | ✅   |