Correct how we find JavaStdlib/ in swiftpm plugin for wrap-java

Plugins/PluginsShared/SwiftJavaPluginProtocol.swift

@@ -23,4 +23,8 @@ extension SwiftJavaPluginProtocol {
   func log(_ message: @autoclosure () -> String, terminator: String = "\n") {
     print("[\(pluginName)] \(message())", terminator: terminator)
   }
+
+  func warn(_ message: @autoclosure () -> String, terminator: String = "\n") {
+    print("[\(pluginName)][warning] \(message())", terminator: terminator)
+  }
 }

Plugins/SwiftJavaPlugin/SwiftJavaPlugin.swift

@@ -242,30 +242,40 @@ extension SwiftJavaBuildToolPlugin {
   func outputFilePath(context: PluginContext, generated: Bool, filename: String) -> URL {
     outputDirectory(context: context, generated: generated).appending(path: filename)
   }
-}
-
-func getExtractedJavaStdlibModules() -> [String] {
-  let fileManager = FileManager.default
-  let sourcesPath = URL(fileURLWithPath: #filePath)
-    .deletingLastPathComponent()
-    .deletingLastPathComponent()
-    .appendingPathComponent("Sources")
-    .appendingPathComponent("JavaStdlib")
-
-  guard let stdlibDirContents = try? fileManager.contentsOfDirectory(
-    at: sourcesPath,
-    includingPropertiesForKeys: [.isDirectoryKey],
-    options: [.skipsHiddenFiles]
-  ) else {
-    return []
-  }
 
-  return stdlibDirContents.compactMap { url in
-    guard let resourceValues = try? url.resourceValues(forKeys: [.isDirectoryKey]),
-          let isDirectory = resourceValues.isDirectory,
-          isDirectory else {
-      return nil
+  func getExtractedJavaStdlibModules() -> [String] {
+    let fileManager = FileManager.default
+    log("Search for JavaStdlib inside: \(#filePath)")
+    let sourcesPath = URL(fileURLWithPath: #filePath)
+      .deletingLastPathComponent()
+      .deletingLastPathComponent()
+      .deletingLastPathComponent()
+      .appendingPathComponent("Sources")
+      .appendingPathComponent("JavaStdlib")
+
+    guard let stdlibDirContents = try? fileManager.contentsOfDirectory(
+      at: sourcesPath,
+      includingPropertiesForKeys: [.isDirectoryKey],
+      options: [.skipsHiddenFiles]
+    ) else {
+      warn("Unable to find Java standard library Swift wrappers! Expected \(sourcesPath) to exist." + 
+           "May be unable to wrap-java types involving Java standard library types.")
+      return []
     }
-    return url.lastPathComponent
-  }.sorted()
+
+    return stdlibDirContents.compactMap { url in
+      let swiftJavaConfigURL = url.appending(path: "swift-java.config")
+      guard fileManager.fileExists(atPath: swiftJavaConfigURL.absoluteString) else {
+        warn("Expected JavaStdlib directory \(url) to contain swift-java.config but it was missing!")
+        return nil
+      }
+
+      guard let resourceValues = try? url.resourceValues(forKeys: [.isDirectoryKey]),
+            let isDirectory = resourceValues.isDirectory,
+            isDirectory else {
+        return nil
+      }
+      return url.lastPathComponent
+    }.sorted()
+  }
 }

Sources/SwiftJavaTool/Commands/WrapJavaCommand.swift

@@ -86,7 +86,7 @@ extension SwiftJava.WrapJavaCommand {
     // Load all of the dependent configurations and associate them with Swift modules.
     let dependentConfigs = try loadDependentConfigs(dependsOn: self.dependsOn).map { moduleName, config in
       guard let moduleName else {
-        throw JavaToSwiftError.badConfigOption
+        throw JavaToSwiftError.badConfigOption(self.dependsOn.joined(separator: " "))
       }
       return (moduleName, config)
     }

Sources/SwiftJavaTool/SwiftJava.swift

@@ -88,14 +88,14 @@ struct SwiftJava: AsyncParsableCommand {
 }
 
 enum JavaToSwiftError: Error {
-  case badConfigOption
+  case badConfigOption(String)
 }
 
 extension JavaToSwiftError: CustomStringConvertible {
   var description: String {
     switch self {
-    case .badConfigOption:
-      "configuration option must be of the form '<swift module name>=<path to config file>"
+    case .badConfigOption(let string):
+      "configuration option must be of the form '<swift module name>=<path to config file>. Was: \(string)"
     }
   }
 }

Tests/SwiftJavaToolLibTests/WrapJavaTests/BasicWrapJavaTests.swift

@@ -198,4 +198,46 @@ final class BasicWrapJavaTests: XCTestCase {
       ]
     )
   }
+
+  func test_wrapJava_inheritFromBiFunction() async throws {
+    let classpathURL = try await compileJava(
+      """
+      package com.example;
+
+      import java.util.function.BiFunction;
+
+      interface CallMe<ValueType> extends BiFunction<ValueType, ValueType, ValueType> {
+        @Override
+        ValueType apply(
+            ValueType newest,
+            ValueType oldest
+        );
+      }
+      """)
+
+    try assertWrapJavaOutput(
+      javaClassNames: [
+        "java.util.function.BiFunction",
+        "com.example.CallMe",
+      ],
+      classpath: [classpathURL],
+      expectedChunks: [
+        """
+        @JavaInterface("com.example.CallMe", extends: BiFunction<ValueType, ValueType, ValueType>.self)
+        public struct CallMe<ValueType: AnyJavaObject> {
+          /**
+           * Java method `apply`.
+           *
+           * ### Java method signature
+           * ```java
+           * public abstract ValueType com.example.CallMe.apply(ValueType,ValueType)
+           * ```
+           */
+          @JavaMethod(typeErasedResult: "ValueType!")
+            public func apply(_ arg0: ValueType?, _ arg1: ValueType?) -> ValueType!
+          }
+        """,
+      ]
+    )
+  }
 }