JExtract: report every skipped declaration; add failOnSkippedDeclarations

Samples/SwiftJavaExtractJNIKotlinSampleApp/Sources/KotlinSampleLibrary/swift-java.config

@@ -1,5 +1,6 @@
 {
   "javaPackage": "com.example.kotlin",
   "mode": "jni",
-  "memoryManagementMode": "allowGlobalAutomatic"
+  "memoryManagementMode": "allowGlobalAutomatic",
+  "failOnSkippedDeclarations": true
 }

Samples/SwiftJavaExtractJNIKotlinSampleApp/Sources/KotlinSampleModels/swift-java.config

@@ -1,5 +1,6 @@
 {
   "javaPackage": "com.example.kotlin.models",
   "mode": "jni",
-  "memoryManagementMode": "allowGlobalAutomatic"
+  "memoryManagementMode": "allowGlobalAutomatic",
+  "failOnSkippedDeclarations": true
 }

Snippets/SwiftJavaCLIHelp.txt

@@ -57,8 +57,9 @@ OPTIONS:
                           and --output-swift.
   -l, --log-level <log-level>
                           Configure the level of logs that should be printed
+                          (default: the config's 'logLevel', or 'info')
                           (values: trace, debug, info, notice, warning, error,
-                          critical; default: log level)
+                          critical)
   --config <config>       A path to a custom swift-java.config to use
   --cp, --classpath <cp>  Class search path of directories and zip/jar files
                           from which Java classes can be loaded.
@@ -115,8 +116,9 @@ OPTIONS:
                           and --output-swift.
   -l, --log-level <log-level>
                           Configure the level of logs that should be printed
+                          (default: the config's 'logLevel', or 'info')
                           (values: trace, debug, info, notice, warning, error,
-                          critical; default: log level)
+                          critical)
   --config <config>       A path to a custom swift-java.config to use
   --cp, --classpath <cp>  Class search path of directories and zip/jar files
                           from which Java classes can be loaded.
@@ -145,8 +147,9 @@ OPTIONS:
                           and --output-swift.
   -l, --log-level <log-level>
                           Configure the level of logs that should be printed
+                          (default: the config's 'logLevel', or 'info')
                           (values: trace, debug, info, notice, warning, error,
-                          critical; default: log level)
+                          critical)
   --config <config>       A path to a custom swift-java.config to use
   --cp, --classpath <cp>  Class search path of directories and zip/jar files
                           from which Java classes can be loaded.
@@ -207,8 +210,9 @@ OPTIONS:
                           and --output-swift.
   -l, --log-level <log-level>
                           Configure the level of logs that should be printed
+                          (default: the config's 'logLevel', or 'info')
                           (values: trace, debug, info, notice, warning, error,
-                          critical; default: log level)
+                          critical)
   --config <config>       A path to a custom swift-java.config to use
   --mode <mode>           The mode of generation to use for the output files.
                           Used with jextract mode.

Sources/JExtractSwiftLib/JNI/JNISwift2JavaGenerator+JavaTranslation.swift

@@ -45,18 +45,27 @@ extension JNISwift2JavaGenerator {
     do {
       translated = try self.javaTranslator.translate(decl)
     } catch {
-      self.logger.debug("Failed to translate: '\(decl.swiftDecl.qualifiedNameForDebug)'; \(error)")
+      reportSkipped(decl.swiftDecl.qualifiedNameForDebug, reason: "\(error)")
       translated = nil
     }
 
     if let candidate = translated, collidesWithThrowableMember(candidate, of: decl) {
+      skippedDeclarations.append("\(decl.swiftDecl.qualifiedNameForDebug): collides with a java.lang.Throwable member")
       translated = nil
     }
 
-    translatedDecls[decl] = translated
+    // `updateValue` so a failure (nil) is cached too; subscript-assigning nil would remove the key.
+    translatedDecls.updateValue(translated, forKey: decl)
     return translated
   }
 
+  /// Logs a declaration that analysis accepted but JNI translation could not handle, and records it
+  /// for `failOnSkippedDeclarations`. These used to be logged at debug level only.
+  private func reportSkipped(_ name: String, reason: String) {
+    self.logger.warning("Failed to translate: '\(name)' in module '\(swiftModuleName)'; \(reason)")
+    skippedDeclarations.append("\(name): \(reason)")
+  }
+
   /// Zero-argument `Throwable` members that a generated `SwiftError` subclass cannot redeclare with another meaning.
   static let throwableMemberNames: Set<String> = [
     "getMessage", "getLocalizedMessage", "getCause", "fillInStackTrace", "printStackTrace", "getStackTrace",
@@ -111,11 +120,11 @@ extension JNISwift2JavaGenerator {
       )
       translated = try translation.translate(enumCase: decl)
     } catch {
-      self.logger.debug("Failed to translate: '\(decl.swiftDecl.qualifiedNameForDebug)'; \(error)")
+      reportSkipped(decl.swiftDecl.qualifiedNameForDebug, reason: "\(error)")
       translated = nil
     }
 
-    translatedEnumCases[decl] = translated
+    translatedEnumCases.updateValue(translated, forKey: decl)
     return translated
   }
 

Sources/JExtractSwiftLib/JNI/JNISwift2JavaGenerator.swift

@@ -44,6 +44,9 @@ package class JNISwift2JavaGenerator: Swift2JavaGenerator {
 
   var thunkNameRegistry = ThunkNameRegistry()
 
+  /// Declarations JNI translation skipped, as "name: reason", for `failOnSkippedDeclarations`.
+  package var skippedDeclarations: [String] = []
+
   /// Jextracted types that already have a minimal JavaKit class wrapper printed for closures.
   var printedMinimalJavaClassWrappers: Set<String> = []
 
@@ -53,8 +56,8 @@ package class JNISwift2JavaGenerator: Swift2JavaGenerator {
   var generatedCDeclSymbolNames: [String] = []
 
   /// Cached Java translation result. 'nil' indicates failed translation.
-  var translatedDecls: [ExtractedFunc: TranslatedFunctionDecl] = [:]
-  var translatedEnumCases: [ExtractedEnumCase: TranslatedEnumCase] = [:]
+  var translatedDecls: [ExtractedFunc: TranslatedFunctionDecl?] = [:]
+  var translatedEnumCases: [ExtractedEnumCase: TranslatedEnumCase?] = [:]
 
   /// Module-qualified identities of extracted types that are surfaced to Java as `SwiftError` exceptions.
   lazy var swiftErrorTypes: Set<SwiftNominalIdentity> = Set(

Sources/JExtractSwiftLib/JavaExtractDecider.swift

@@ -16,13 +16,17 @@ import SwiftExtract
 import SwiftJavaConfigurationShared
 import SwiftSyntax
 
-public func makeSwiftJavaAnalyzer(config: Configuration) -> SwiftAnalyzer {
+public func makeSwiftJavaAnalyzer(
+  config: Configuration,
+  diagnosticsSink: (any SwiftExtractDiagnosticsSink)? = nil
+) -> SwiftAnalyzer {
   SwiftAnalyzer(
     config: config,
     extractDecider: JavaExtractDecider(
       accessLevel: config.effectiveMinimumInputAccessLevelMode,
       logLevel: config.logLevel ?? .info
     ),
+    diagnosticsSink: diagnosticsSink
   )
 }
 

Sources/JExtractSwiftLib/Swift2Java.swift

@@ -37,7 +37,8 @@ public struct SwiftToJava {
 
     let javaPackage = try validateJavaPackage(config.javaPackage)
 
-    let translator = makeSwiftJavaAnalyzer(config: config)
+    let skippedDuringAnalysis = SkippedDeclarationCollector()
+    let translator = makeSwiftJavaAnalyzer(config: config, diagnosticsSink: skippedDuringAnalysis)
     let log = translator.log
 
     guard let inputSwift = config.inputSwiftDirectory else {
@@ -128,6 +129,7 @@ public struct SwiftToJava {
       )
 
       try generator.generate()
+      try failIfSkipped(skippedDuringAnalysis.skipped, module: swiftModule, log: log)
 
     case .jni:
       let generator = JNISwift2JavaGenerator(
@@ -141,11 +143,20 @@ public struct SwiftToJava {
       )
 
       try generator.generate()
+      try failIfSkipped(skippedDuringAnalysis.skipped + generator.skippedDeclarations, module: swiftModule, log: log)
     }
 
     print("[swift-java] Imported Swift module '\(swiftModule)': " + "done.".green)
   }
 
+  /// With `failOnSkippedDeclarations`, turns skipped declarations into a failure that lists them all.
+  package func failIfSkipped(_ skipped: [String], module: String, log: Logger) throws {
+    guard config.effectiveFailOnSkippedDeclarations, !skipped.isEmpty else {
+      return
+    }
+    throw SkippedDeclarationsError(module: module, skipped: skipped)
+  }
+
   /// Compute a relative path (sans `.swift` extension) for a file against the
   /// input paths, suitable for jextract filter matching
   func computeRelativePath(file: URL, inputPaths: [URL]) -> String {
@@ -267,3 +278,29 @@ private func collectFilesFromPath(
   }
   allFiles.append(path)
 }
+
+/// Collects declarations skipped during analysis.
+package final class SkippedDeclarationCollector: SwiftExtractDiagnosticsSink {
+  package private(set) var skipped: [String] = []
+
+  package init() {}
+
+  package func emit(_ diagnostic: SwiftExtractDiagnostic) {
+    guard case .skippedDeclaration = diagnostic.kind else { return }
+    skipped.append("\(diagnostic.declarationName): \(diagnostic.message)")
+  }
+}
+
+package struct SkippedDeclarationsError: Error, CustomStringConvertible {
+  let module: String
+  let skipped: [String]
+
+  // The list goes in the error itself: the tool fails through `fatalError`, which doesn't flush
+  // log lines written to a piped stdout (as when run by the SwiftPM plugin).
+  package var description: String {
+    """
+    jextract skipped \(skipped.count) declaration(s) in module '\(module)' and 'failOnSkippedDeclarations' is set:
+    \(skipped.map { "  - \($0)" }.joined(separator: "\n"))
+    """
+  }
+}

Sources/SwiftJavaConfigurationShared/Configuration.swift

@@ -181,6 +181,13 @@ public struct Configuration: Codable {
     enableJavaCallbacks ?? false
   }
 
+  /// If true, JExtract fails after generating when it skipped any declaration it could not
+  /// extract or translate, and lists each one. Skipped declarations are always reported as warnings.
+  public var failOnSkippedDeclarations: Bool?
+  public var effectiveFailOnSkippedDeclarations: Bool {
+    failOnSkippedDeclarations ?? false
+  }
+
   /// If specified, JExtract will output to this file a list of paths to all generated Java source files.
   public var generatedJavaSourcesListFileOutput: String?
 

Sources/SwiftJavaDocumentation/Documentation.docc/SwiftJavaConfigFile.md

@@ -246,6 +246,16 @@ only supported in `jni` mode.
 
 ---
 
+#### failOnSkippedDeclarations
+
+- **Type:** `Bool?`
+- **Default:** `false`
+
+If true, JExtract fails after generating when it skipped any declaration it could not
+extract or translate, and lists each one. Skipped declarations are always reported as warnings.
+
+---
+
 #### generatedJavaSourcesListFileOutput
 
 - **Type:** `String?`

Sources/SwiftJavaTool/CommonOptions.swift

@@ -63,8 +63,11 @@ extension SwiftJava {
     )
     var inputSwift: String? = nil
 
-    @Option(name: .shortAndLong, help: "Configure the level of logs that should be printed")
-    var logLevel: LogLevel = .info
+    @Option(
+      name: .shortAndLong,
+      help: "Configure the level of logs that should be printed (default: the config's 'logLevel', or 'info')"
+    )
+    var logLevel: LogLevel? = nil
 
     @Option(help: "A path to a custom swift-java.config to use")
     var config: String? = nil

Sources/SwiftJavaTool/SwiftJavaBaseAsyncParsableCommand.swift

@@ -106,7 +106,7 @@ extension SwiftJavaBaseAsyncParsableCommand {
 
   var logLevel: LogLevel {
     get {
-      self.commonOptions.logLevel
+      self.commonOptions.logLevel ?? .info
     }
     set {
       self.commonOptions.logLevel = newValue
@@ -183,7 +183,11 @@ extension SwiftJavaBaseAsyncParsableCommand {
       config = Configuration()
     }
     // override configuration with options from command line
-    config.logLevel = command.logLevel
+    if let logLevel = command.commonOptions.logLevel {
+      config.logLevel = logLevel
+    } else if config.logLevel == nil {
+      config.logLevel = .info
+    }
     return config
   }
 }

Tests/JExtractSwiftTests/JNI/JNISkippedDeclarationsTests.swift

@@ -0,0 +1,91 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2026 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 CodePrinting
+import JExtractSwiftLib
+import SwiftExtract
+import SwiftJavaConfigurationShared
+import Testing
+
+/// Declarations jextract skips are reported, and `failOnSkippedDeclarations` turns them into a failure.
+@Suite
+struct JNISkippedDeclarationsTests {
+  let source =
+    """
+    public struct Tag {
+      public var name: String
+    }
+    public func supported() -> Tag { fatalError() }
+    public func sparse() -> [Tag?] { [] }
+    public func nested() -> [[String: Int64]] { [] }
+    """
+
+  private func generate(_ source: String, sink: SkippedDeclarationCollector? = nil) throws -> JNISwift2JavaGenerator {
+    var config = Configuration()
+    config.swiftModule = "SwiftModule"
+    let translator = makeSwiftJavaAnalyzer(config: config, diagnosticsSink: sink)
+    try translator.analyze(path: "/fake/Fake.swiftinterface", text: source)
+    let generator = JNISwift2JavaGenerator(
+      config: config,
+      translator: translator,
+      javaPackage: "com.example.swift",
+      swiftOutputDirectory: "/fake",
+      javaOutputDirectory: "/fake",
+      javaClassLookupTable: [:],
+      moduleJavaPackages: [:]
+    )
+    var javaPrinter = JavaPrinter(mode: .accumulateAll)
+    try generator.writeExportedJavaSources(&javaPrinter)
+    var swiftPrinter = SwiftPrinter(mode: .accumulateAll)
+    try generator.writeSwiftThunkSources(&swiftPrinter)
+    return generator
+  }
+
+  @Test
+  func translationFailuresAreRecordedOnce() throws {
+    let generator = try generate(source)
+    let skipped = generator.skippedDeclarations.sorted()
+    #expect(skipped.count == 2, "\(skipped)")
+    #expect(skipped[0].hasPrefix("nested()"))
+    #expect(skipped[1].hasPrefix("sparse()"))
+  }
+
+  @Test
+  func analysisSkipsAreCollected() throws {
+    let sink = SkippedDeclarationCollector()
+    _ = try generate("public struct S { public static let untyped = 42 }", sink: sink)
+    #expect(sink.skipped.count == 1, "\(sink.skipped)")
+    #expect(sink.skipped.first?.hasPrefix("S.untyped") == true)
+  }
+
+  @Test
+  func failsOnlyWhenConfigured() throws {
+    let skipped = ["sparse(): unsupported"]
+    var config = Configuration()
+    let log = Logger(label: "test", logLevel: .critical)
+
+    #expect(throws: Never.self) {
+      try SwiftToJava(config: config, dependencyConfigs: []).failIfSkipped(skipped, module: "M", log: log)
+    }
+
+    config.failOnSkippedDeclarations = true
+    let error = #expect(throws: SkippedDeclarationsError.self) {
+      try SwiftToJava(config: config, dependencyConfigs: []).failIfSkipped(skipped, module: "M", log: log)
+    }
+    #expect(error?.description.contains("  - sparse(): unsupported") == true)
+    #expect(throws: Never.self) {
+      try SwiftToJava(config: config, dependencyConfigs: []).failIfSkipped([], module: "M", log: log)
+    }
+  }
+}