jextract: generate one output swift file per input file (#403)

Author: ktoso

Plugins/JExtractSwiftPlugin/JExtractSwiftPlugin.swift

@@ -93,6 +93,7 @@ struct JExtractSwiftBuildToolPlugin: SwiftJavaPluginProtocol, BuildToolPlugin {
       $0.pathExtension == "swift"
     }
 
+    // Output Swift files are just Java filename based converted to Swift files one-to-one
     var outputSwiftFiles: [URL] = swiftFiles.compactMap { sourceFileURL in
       guard sourceFileURL.isFileURL else {
         return nil as URL?
@@ -102,7 +103,7 @@ struct JExtractSwiftBuildToolPlugin: SwiftJavaPluginProtocol, BuildToolPlugin {
       guard sourceFilePath.starts(with: sourceDir) else {
         fatalError("Could not get relative path for source file \(sourceFilePath)")
       }
-      var outputURL = outputSwiftDirectory
+      let outputURL = outputSwiftDirectory
         .appending(path: String(sourceFilePath.dropFirst(sourceDir.count).dropLast(sourceFileURL.lastPathComponent.count + 1)))
 
       let inputFileName = sourceFileURL.deletingPathExtension().lastPathComponent
@@ -116,11 +117,12 @@ struct JExtractSwiftBuildToolPlugin: SwiftJavaPluginProtocol, BuildToolPlugin {
 
     // If the module uses 'Data' type, the thunk file is emitted as if 'Data' is declared
     // in that module. Declare the thunk file as the output.
-    // FIXME: Make this conditional.
     outputSwiftFiles += [
-      outputSwiftDirectory.appending(path: "Data+SwiftJava.swift")
+      outputSwiftDirectory.appending(path: "Foundation+SwiftJava.swift")
     ]
 
+    print("[swift-java-plugin] Output swift files:\n - \(outputSwiftFiles.map({$0.absoluteString}).joined(separator: "\n - "))")
+
     return [
       .buildCommand(
         displayName: "Generate Java wrappers for Swift types",

Samples/SwiftJavaExtractFFMSampleApp/Sources/MySwiftLibrary/MultiplePublicTypes.swift

@@ -0,0 +1,26 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// This file exists to exercise the swiftpm plugin generating separate output Java files 
+// for the public types; because Java public types must be in a file with the same name as the type.
+
+public struct PublicTypeOne {
+  public init() {}
+  public func test() {}
+}
+
+public struct PublicTypeTwo { 
+  public init() {}
+  public func test() {}
+}

Samples/SwiftJavaExtractFFMSampleApp/ci-validate.sh

@@ -3,5 +3,7 @@
 set -x
 set -e
 
+swift build # as a workaround for building swift build from within gradle having issues on CI sometimes
+
 ./gradlew run
 ./gradlew test

Samples/SwiftJavaExtractFFMSampleApp/src/test/java/com/example/swift/MultipleTypesFromSingleFileTest.java

@@ -0,0 +1,36 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+package com.example.swift;
+
+import org.junit.jupiter.api.Test;
+import org.swift.swiftkit.core.*;
+import org.swift.swiftkit.ffm.*;
+
+import java.lang.foreign.Arena;
+import java.util.Optional;
+import java.util.OptionalInt;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+public class MultipleTypesFromSingleFileTest {
+    
+    @Test
+    void bothTypesMustHaveBeenGenerated() {
+        try (var arena = AllocatingSwiftArena.ofConfined()) {
+            PublicTypeOne.init(arena);
+            PublicTypeTwo.init(arena);
+        }
+    }
+}

Samples/SwiftJavaExtractJNISampleApp/Sources/MySwiftLibrary/MultiplePublicTypes.swift

@@ -0,0 +1,26 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// This file exists to exercise the swiftpm plugin generating separate output Java files 
+// for the public types; because Java public types must be in a file with the same name as the type.
+
+public struct PublicTypeOne { 
+  public init() {}
+  public func test() {}
+}
+
+public struct PublicTypeTwo { 
+  public init() {}
+  public func test() {}
+}

Samples/SwiftJavaExtractJNISampleApp/build.gradle

@@ -102,7 +102,8 @@ def jextract = tasks.register("jextract", Exec) {
 
     workingDir = layout.projectDirectory
     commandLine "swift"
-    args("build") // since Swift targets which need to be jextract-ed have the jextract build plugin, we just need to build
+    // TODO: -v for debugging build issues...
+    args("build", "-v") // since Swift targets which need to be jextract-ed have the jextract build plugin, we just need to build
     // If we wanted to execute a specific subcommand, we can like this:
     //     args("run",/*
     //             "swift-java", "jextract",

Samples/SwiftJavaExtractJNISampleApp/ci-validate.sh

@@ -3,5 +3,7 @@
 set -x
 set -e
 
+swift build # as a workaround for building swift build from within gradle having issues on CI sometimes
+
 ./gradlew run
 ./gradlew test

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

@@ -0,0 +1,36 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+package com.example.swift;
+
+import org.junit.jupiter.api.Test;
+import org.swift.swiftkit.core.ConfinedSwiftMemorySession;
+import org.swift.swiftkit.core.SwiftArena;
+
+import java.lang.foreign.Arena;
+import java.util.Optional;
+import java.util.OptionalInt;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+public class MultipleTypesFromSingleFileTest {
+    
+    @Test
+    void bothTypesMustHaveBeenGenerated() {
+        try (var arena = SwiftArena.ofConfined()) {
+            PublicTypeOne.init(arena);
+            PublicTypeTwo.init(arena);
+        }
+    }
+}

Sources/JExtractSwiftLib/CodePrinter.swift

@@ -216,14 +216,28 @@ extension CodePrinter {
 
   /// - Returns: the output path of the generated file, if any (i.e. not in accumulate in memory mode)
   package mutating func writeContents(
-    outputDirectory: String,
+    outputDirectory _outputDirectory: String,
     javaPackagePath: String?,
-    filename: String
+    filename _filename: String
   ) throws -> URL? {
+
+    // We handle 'filename' that has a path, since that simplifies passing paths from root output directory enourmously.
+    // This just moves the directory parts into the output directory part in order for us to create the sub-directories.
+    let outputDirectory: String
+    let filename: String
+    if _filename.contains(PATH_SEPARATOR) {
+      let parts = _filename.split(separator: PATH_SEPARATOR)
+      outputDirectory = _outputDirectory.appending(PATH_SEPARATOR).appending(parts.dropLast().joined(separator: PATH_SEPARATOR))
+      filename = "\(parts.last!)"
+    } else {
+      outputDirectory = _outputDirectory
+      filename = _filename
+    }
+
     guard self.mode != .accumulateAll else {
       // if we're accumulating everything, we don't want to finalize/flush any contents
       // let's mark that this is where a write would have happened though:
-      print("// ^^^^ Contents of: \(outputDirectory)/\(filename)")
+      print("// ^^^^ Contents of: \(outputDirectory)\(PATH_SEPARATOR)\(filename)")
       return nil
     }
 
@@ -233,7 +247,7 @@ extension CodePrinter {
         "// ==== ---------------------------------------------------------------------------------------------------"
       )
       if let javaPackagePath {
-        print("// \(javaPackagePath)/\(filename)")
+        print("// \(javaPackagePath)\(PATH_SEPARATOR)\(filename)")
       } else {
         print("// \(filename)")
       }
@@ -242,9 +256,15 @@ extension CodePrinter {
     }
 
     let targetDirectory = [outputDirectory, javaPackagePath].compactMap { $0 }.joined(separator: PATH_SEPARATOR)
-    log.trace("Prepare target directory: \(targetDirectory)")
-    try FileManager.default.createDirectory(
-      atPath: targetDirectory, withIntermediateDirectories: true)
+    log.debug("Prepare target directory: '\(targetDirectory)' for file \(filename.bold)")
+    do {
+      try FileManager.default.createDirectory(
+        atPath: targetDirectory, withIntermediateDirectories: true)
+    } catch {
+      // log and throw since it can be confusing what the reason for failing the write was otherwise
+      log.warning("Failed to create directory: \(targetDirectory)")
+      throw error
+    }
 
     let outputPath = Foundation.URL(fileURLWithPath: targetDirectory).appendingPathComponent(filename)
     try contents.write(

Sources/JExtractSwiftLib/FFM/FFMSwift2JavaGenerator+SwiftThunkPrinting.swift

@@ -22,8 +22,16 @@ extension FFMSwift2JavaGenerator {
   }
 
   package func writeSwiftExpectedEmptySources() throws {
+    let pendingFileCount = self.expectedOutputSwiftFiles.count
+    guard pendingFileCount > 0 else {
+      return // no need to write any empty files, yay
+    }
+    
+    print("[swift-java] Write empty [\(self.expectedOutputSwiftFiles.count)] 'expected' files in: \(swiftOutputDirectory)/")
+    
     for expectedFileName in self.expectedOutputSwiftFiles {
-      log.trace("Write empty file: \(expectedFileName) ...")
+      log.debug("Write SwiftPM-'expected' empty file: \(expectedFileName.bold)")
+
 
       var printer = CodePrinter()
       printer.print("// Empty file generated on purpose")
@@ -46,32 +54,49 @@ extension FFMSwift2JavaGenerator {
         outputDirectory: self.swiftOutputDirectory,
         javaPackagePath: nil,
         filename: moduleFilename) {
-        print("[swift-java] Generated: \(moduleFilenameBase.bold).swift (at \(outputFile))")
+        log.info("Generated: \(moduleFilenameBase.bold).swift (at \(outputFile.absoluteString))")
         self.expectedOutputSwiftFiles.remove(moduleFilename)
       }
     } catch {
       log.warning("Failed to write to Swift thunks: \(moduleFilename)")
     }
 
     // === All types
-    // FIXME: write them all into the same file they were declared from +SwiftJava
-    for (_, ty) in self.analysis.importedTypes.sorted(by: { (lhs, rhs) in lhs.key < rhs.key }) {
-      let fileNameBase = "\(ty.swiftNominal.qualifiedName)+SwiftJava"
-      let filename = "\(fileNameBase).swift"
-      log.debug("Printing contents: \(filename)")
+    // We have to write all types to their corresponding output file that matches the file they were declared in,
+    // because otherwise SwiftPM plugins will not pick up files apropriately -- we expect 1 output +SwiftJava.swift file for every input.
+    for group: (key: String, value: [Dictionary<String, ImportedNominalType>.Element]) in Dictionary(grouping: self.analysis.importedTypes, by: { $0.value.sourceFilePath }) {
+      log.warning("Writing types in file group: \(group.key): \(group.value.map(\.key))")
+
+      let importedTypesForThisFile = group.value
+        .map(\.value)
+        .sorted(by: { $0.qualifiedName < $1.qualifiedName })
+
+      let inputFileName = "\(group.key)".split(separator: "/").last ?? "__Unknown.swift"
+      let filename = "\(inputFileName)".replacing(".swift", with: "+SwiftJava.swift")
+
+      for ty in importedTypesForThisFile {
+        log.info("Printing Swift thunks for type: \(ty.qualifiedName.bold)")
+        printer.printSeparator("Thunks for \(ty.qualifiedName)")
+
+        do {
+          try printSwiftThunkSources(&printer, ty: ty)
+        } catch {
+          log.warning("Failed to print to Swift thunks for type'\(ty.qualifiedName)' to '\(filename)', error: \(error)")
+        }
+        
+      }
 
+      log.warning("Write Swift thunks file: \(filename.bold)")
       do {
-        try printSwiftThunkSources(&printer, ty: ty)
-
         if let outputFile = try printer.writeContents(
           outputDirectory: self.swiftOutputDirectory,
           javaPackagePath: nil,
           filename: filename) {
-          print("[swift-java] Generated: \(fileNameBase.bold).swift (at \(outputFile))")
+          log.info("Done writing Swift thunks to: \(outputFile.absoluteString)")
           self.expectedOutputSwiftFiles.remove(filename)
         }
       } catch {
-        log.warning("Failed to write to Swift thunks: \(filename)")
+        log.warning("Failed to write to Swift thunks: \(filename), error: \(error)")
       }
     }
   }