jextract/jni: Fix compilation of nested generic types

Samples/SwiftJavaExtractJNISampleApp/Sources/MySwiftLibrary/NestedTypes.swift

@@ -50,4 +50,8 @@ public enum NamespaceEnum {
   public enum Nested {
     public static func something() {}
   }
+
+  public struct NestedGenericType<T> {
+    public var value: Int
+  }
 }

Sources/JExtractSwiftLib/ImportedDecls.swift

@@ -167,7 +167,7 @@ package final class ImportedNominalType: ImportedDecl {
   }
 
   var swiftType: SwiftType {
-    .nominal(.init(nominalTypeDecl: swiftNominal))
+    swiftNominal.asSwiftType
   }
 
   /// Structured Java-facing type name — "FishBox" for specialized, "Box" for base

Sources/JExtractSwiftLib/JNI/JNISwift2JavaGenerator+SwiftThunkPrinting.swift

@@ -920,7 +920,7 @@ extension JNISwift2JavaGenerator {
   }
 
   private func openerProtocolName(for type: SwiftNominalTypeDeclaration) -> String {
-    "_\(swiftModuleName)_\(type.name)_opener"
+    "_\(swiftModuleName)_\(type.flatName)_opener"
   }
 
   private func printOpenerProtocol(_ printer: inout CodePrinter, _ type: ImportedNominalType) {
@@ -969,7 +969,7 @@ extension JNISwift2JavaGenerator {
       }
     }
     printer.println()
-    printer.printBraceBlock("extension \(type.swiftNominal.name): \(protocolName)") { printer in
+    printer.printBraceBlock("extension \(type.swiftNominal.qualifiedName): \(protocolName)") { printer in
       for variable in type.variables {
         if variable.isStatic { continue }
         printFunctionDecl(&printer, decl: variable, skipMethodBody: false)

Sources/JExtractSwiftLib/SwiftTypes/SwiftType.swift

@@ -589,3 +589,18 @@ enum TypeTranslationError: Error {
   /// Unknown nominal type.
   case unknown(TypeSyntax, file: StaticString = #file, line: Int = #line)
 }
+
+extension SwiftNominalTypeDeclaration {
+  var asSwiftNominalType: SwiftNominalType {
+    let genericArguments = genericParameters.map { SwiftType.genericParameter($0) }
+    return SwiftNominalType(
+      parent: parent?.asSwiftNominalType,
+      nominalTypeDecl: self,
+      genericArguments: genericArguments.isEmpty ? nil : genericArguments
+    )
+  }
+
+  var asSwiftType: SwiftType {
+    .nominal(asSwiftNominalType)
+  }
+}

Tests/JExtractSwiftTests/JNI/JNIGenericTypeTests.swift

@@ -121,7 +121,7 @@ struct JNIGenericTypeTests {
           static func _get_description(environment: UnsafeMutablePointer<JNIEnv?>!, thisClass: jclass, selfPointer: jlong) -> jstring? {
             assert(selfPointer != 0, "selfPointer memory address was null")
             let selfPointerBits$ = Int(Int64(fromJNI: selfPointer, in: environment))
-            let selfPointer$ = UnsafeMutablePointer<MyID>(bitPattern: selfPointerBits$)
+            let selfPointer$ = UnsafeMutablePointer<MyID<T>>(bitPattern: selfPointerBits$)
             guard let selfPointer$ else {
               fatalError("selfPointer memory address was null in call to \(#function)!")
             }
@@ -239,7 +239,6 @@ struct JNIGenericTypeTests {
       ]
     )
 
-
     try assertOutput(
       input: input,
       .jni,
@@ -253,6 +252,39 @@ struct JNIGenericTypeTests {
     )
   }
 
+  @Test
+  func nestedGenericType() throws {
+    let input =
+      #"""
+      public enum Foo {
+        public struct Bar<T> {
+          public func work() {}
+        }
+      }
+      """#
+
+    try assertOutput(
+      input: input,
+      .jni,
+      .swift,
+      detectChunkByInitialLines: 1,
+      expectedChunks: [
+        #"""
+        extension Foo.Bar: _SwiftModule_Foo_Bar_opener {
+          static func _work(environment: UnsafeMutablePointer<JNIEnv?>!, thisClass: jclass, selfPointer: jlong) {
+            ...
+            let selfPointer$ = UnsafeMutablePointer<Foo.Bar<T>>(bitPattern: selfPointerBits$)
+            guard let selfPointer$ else {
+             fatalError("selfPointer memory address was null in call to \(#function)!")
+            }
+            selfPointer$.pointee.work()
+          }
+        }
+        """#
+      ],
+    )
+  }
+
   @Test("Constrained extensions are ignored")
   func constrainedExtensionsAreIgnored() throws {
     let input =