Redesign jextract-swift: plugins and avoid custom swift features

We now heavily rely on Swift thunk generation and call into those C
calling convention compatible APIs from Java. They translate into member
calls on classes -- this way we'll be able to also do structs and other
things.

This also introduces gradle to "drive" the `swift package jextract`
plugin. This allows us for samples to be a plain `./gradlew run`,
and no more manual running of any make or other swift interface
generation steps etc.

This is a big milestone towards getting "just works" builds with the
jextract route.

Follow ups will handle more java library path handling and more types of
calls we can make, like variables, and importing structs etc.

Author: ktoso

.github/workflows/pull_request.yml

@@ -19,7 +19,8 @@ jobs:
     strategy:
       fail-fast: true
       matrix:
-        swift_version: ['nightly-main']
+        # swift_version: ['nightly-main']
+        swift_version: ['6.0.2']
         os_version: ['jammy']
         jdk_vendor: ['Corretto']
     container:
@@ -43,8 +44,8 @@ jobs:
         if: steps.cache-jdk.outputs.cache-hit != 'true'
         run: "bash -xc 'JDK_VENDOR=${{ matrix.jdk_vendor }} ./docker/install_jdk.sh'"
         # TODO: not using setup-java since incompatible with the swiftlang/swift base image
-      - name: Install Untested Nightly Swift
-        run: "bash -xc './docker/install_untested_nightly_swift.sh'"
+        #      - name: Install Untested Nightly Swift
+        #        run: "bash -xc './docker/install_untested_nightly_swift.sh'"
       - name: Cache local Gradle repository
         uses: actions/cache@v4
         continue-on-error: true
@@ -79,7 +80,8 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        swift_version: ['nightly-main']
+        # swift_version: ['nightly-main']
+        swift_version: ['6.0.2']
         os_version: ['jammy']
         jdk_vendor: ['Corretto']
     container:
@@ -103,8 +105,8 @@ jobs:
         if: steps.cache-jdk.outputs.cache-hit != 'true'
         run: "bash -xc 'JDK_VENDOR=${{ matrix.jdk_vendor }} ./docker/install_jdk.sh'"
         # TODO: not using setup-java since incompatible with the swiftlang/swift base image
-      - name: Install Untested Nightly Swift
-        run: "bash -xc './docker/install_untested_nightly_swift.sh'"
+        #      - name: Install Untested Nightly Swift
+        #        run: "bash -xc './docker/install_untested_nightly_swift.sh'"
       - name: Cache local Gradle repository
         uses: actions/cache@v4
         continue-on-error: true
@@ -125,9 +127,9 @@ jobs:
             ${{ runner.os }}-swiftpm-cache
             ${{ runner.os }}-swiftpm-
       # run the actual build
-      - name: Generate sources (make) (Temporary)
-        # TODO: this should be triggered by the respective builds
-        run: "make jextract-generate"
+      # - name: Generate sources (make) (Temporary)
+      #  # TODO: this should be triggered by the respective builds
+      #  run: "make jextract-generate"
       - name: Test Swift
         run: "swift test"
       - name: Build (Swift) Sample Apps

.licenseignore

@@ -37,3 +37,5 @@ Makefile
 gradle/wrapper/gradle-wrapper.properties
 gradlew
 gradlew.bat
+**/gradlew
+**/gradlew.bat

Makefile

@@ -57,8 +57,6 @@ all:
 	@echo "Welcome to swift-java! There are several makefile targets to choose from:"
 	@echo "  javakit-run: Run the JavaKit example program that uses Java libraries from Swift."
 	@echo "  javakit-generate: Regenerate the Swift wrapper code for the various JavaKit libraries from Java. This only has to be done when changing the Java2Swift tool."
-	@echo "  jextract-run: Run the Java example code that uses the wrapped Swift library. NOTE: this requires development toolchain described in the README."
-	@echo "  jextract-generate: Generate Java wrapper code for the example Swift library allowing Swift to be called from Java. NOTE: this requires development toolchain described in the README."
 
 $(BUILD_DIR)/debug/libJavaKit.$(LIB_SUFFIX) $(BUILD_DIR)/debug/Java2Swift:
 	swift build
@@ -105,42 +103,5 @@ format:
 ### "SwiftKit" is the "call swift from java"  ###
 #################################################
 
-JEXTRACT_BUILD_DIR="$(BUILD_DIR)/jextract"
-
-define make_swiftinterface
-    $(eval $@_MODULE = $(1))
-    $(eval $@_FILENAME = $(2))
-	eval ${SWIFTC} \
-		-emit-module-interface-path ${JEXTRACT_BUILD_DIR}/${$@_MODULE}/${$@_FILENAME}.swiftinterface \
-		-emit-module-path ${JEXTRACT_BUILD_DIR}/${$@_MODULE}/${$@_FILENAME}.swiftmodule \
-		-enable-library-evolution \
-		-Xfrontend -abi-comments-in-module-interface \
-		-module-name ${$@_MODULE} \
-		-Xfrontend -abi-comments-in-module-interface \
-		Sources/${$@_MODULE}/${$@_FILENAME}.swift
-	echo "Generated: ${JEXTRACT_BUILD_DIR}/${$@_MODULE}/${$@_FILENAME}.swiftinterface"
-endef
-
-jextract-swift: generate-JExtract-interface-files
-	swift build
-
-generate-JExtract-interface-files: $(BUILD_DIR)/debug/libJavaKit.$(LIB_SUFFIX)
-	@echo "Generate .swiftinterface files..."
-	@$(call make_swiftinterface, "ExampleSwiftLibrary", "MySwiftLibrary")
-	@$(call make_swiftinterface, "SwiftKitSwift", "SwiftKit")
-
-jextract-generate: jextract-swift generate-JExtract-interface-files
-	swift run jextract-swift  \
-		--package-name com.example.swift.generated \
-		--swift-module ExampleSwiftLibrary \
-		--output-directory ${SAMPLES_DIR}/SwiftKitSampleApp/build/generated/sources/jextract/main \
-		$(BUILD_DIR)/jextract/ExampleSwiftLibrary/MySwiftLibrary.swiftinterface; \
-	swift run jextract-swift \
-		--package-name org.swift.swiftkit.generated \
-		--swift-module SwiftKitSwift \
-		--output-directory ${SAMPLES_DIR}/SwiftKitSampleApp/build/generated/sources/jextract/main \
-		$(BUILD_DIR)/jextract/SwiftKitSwift/SwiftKit.swiftinterface
-
-
 jextract-run: jextract-generate
 	./gradlew Samples:SwiftKitSampleApp:run

Package.swift

@@ -126,6 +126,14 @@ let package = Package(
       targets: ["JExtractSwift"]
     ),
 
+    // ==== Plugin for wrapping Java classes in Swift
+    .plugin(
+      name: "JExtractSwiftPlugin",
+      targets: [
+        "JExtractSwiftPlugin"
+      ]
+    ),
+
     // ==== Examples
 
     .library(
@@ -229,6 +237,7 @@ let package = Package(
         .unsafeFlags(["-I\(javaIncludePath)", "-I\(javaPlatformIncludePath)"])
       ]
     ),
+
     .plugin(
       name: "JavaCompilerPlugin",
       capability: .buildTool()
@@ -331,6 +340,14 @@ let package = Package(
       ]
     ),
 
+    .plugin(
+      name: "JExtractSwiftPlugin",
+      capability: .buildTool(),
+      dependencies: [
+        "JExtractSwiftTool"
+      ]
+    ),
+
     .testTarget(
       name: "JavaKitTests",
       dependencies: ["JavaKit", "JavaKitNetwork"],

Plugins/JExtractSwiftPlugin/Configuration.swift

@@ -0,0 +1,36 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+import Foundation
+
+/// Configuration for the JExtractSwift translation tool, provided on a per-target
+/// basis.
+struct Configuration: Codable {
+  var javaPackage: String
+}
+
+func readConfiguration(sourceDir: String) throws -> Configuration {
+  let configFile = URL(filePath: sourceDir).appending(path: "JExtractSwift.config")
+  do {
+    let configData = try Data(contentsOf: configFile)
+    return try JSONDecoder().decode(Configuration.self, from: configData)
+  } catch {
+    throw ConfigurationError(message: "Failed to parse JExtractSwift configuration at '\(configFile)!'", error: error)
+  }
+}
+
+struct ConfigurationError: Error {
+  let message: String
+  let error: any Error
+}

Plugins/JExtractSwiftPlugin/JExtractSwiftPlugin.swift

@@ -0,0 +1,85 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+import Foundation
+import PackagePlugin
+
+@main
+struct JExtractSwiftBuildToolPlugin: BuildToolPlugin {
+  func createBuildCommands(context: PluginContext, target: Target) throws -> [Command] {
+    guard let sourceModule = target.sourceModule else { return [] }
+
+    // Note: Target doesn't have a directoryURL counterpart to directory,
+    // so we cannot eliminate this deprecation warning.
+    let sourceDir = target.directory.string
+
+    let configuration = try readConfiguration(sourceDir: "\(sourceDir)")
+
+    // We use the the usual maven-style structure of "src/[generated|main|test]/java/..."
+    // that is common in JVM ecosystem
+    let outputDirectoryJava = context.pluginWorkDirectoryURL
+      .appending(path: "src")
+      .appending(path: "generated")
+      .appending(path: "java")
+    let outputDirectorySwift = context.pluginWorkDirectoryURL
+      .appending(path: "src")
+      .appending(path: "generated")
+      .appending(path: "Sources")
+
+    var arguments: [String] = [
+      "--swift-module", sourceModule.name,
+      "--package-name", configuration.javaPackage,
+      "--output-directory-java", outputDirectoryJava.path(percentEncoded: false),
+      "--output-directory-swift", outputDirectorySwift.path(percentEncoded: false),
+      // TODO: "--build-cache-directory", ...
+      //       Since plugins cannot depend on libraries we cannot detect what the output files will be,
+      //       as it depends on the contents of the input files. Therefore we have to implement this as a prebuild plugin.
+      //       We'll have to make up some caching inside the tool so we don't re-parse files which have not changed etc.
+    ]
+    arguments.append(sourceDir)
+
+    return [
+      .prebuildCommand(
+        displayName: "Generate Java wrappers for Swift types",
+        executable: try context.tool(named: "JExtractSwiftTool").url,
+        arguments: arguments,
+        // inputFiles: [ configFile ] + swiftFiles,
+        // outputFiles: outputJavaFiles
+        outputFilesDirectory: outputDirectorySwift
+      )
+    ]
+  }
+}
+
+// Note: the JAVA_HOME environment variable must be set to point to where
+// Java is installed, e.g.,
+//   Library/Java/JavaVirtualMachines/openjdk-21.jdk/Contents/Home.
+func findJavaHome() -> String {
+  if let home = ProcessInfo.processInfo.environment["JAVA_HOME"] {
+    return home
+  }
+
+  // This is a workaround for envs (some IDEs) which have trouble with
+  // picking up env variables during the build process
+  let path = "\(FileManager.default.homeDirectoryForCurrentUser.path()).java_home"
+  if let home = try? String(contentsOfFile: path, encoding: .utf8) {
+    if let lastChar = home.last, lastChar.isNewline {
+      return String(home.dropLast())
+    }
+
+    return home
+  }
+
+  fatalError("Please set the JAVA_HOME environment variable to point to where Java is installed.")
+}

Samples/JExtractPluginSampleApp/.gitignore

@@ -0,0 +1,8 @@
+.DS_Store
+/.build
+/Packages
+xcuserdata/
+DerivedData/
+.swiftpm/configuration/registries.json
+.swiftpm/xcode/package.xcworkspace/contents.xcworkspacedata
+.netrc

Samples/JExtractPluginSampleApp/Package.swift

@@ -0,0 +1,70 @@
+// swift-tools-version: 6.0
+// The swift-tools-version declares the minimum version of Swift required to build this package.
+
+import PackageDescription
+
+import class Foundation.FileManager
+import class Foundation.ProcessInfo
+
+// Note: the JAVA_HOME environment variable must be set to point to where
+// Java is installed, e.g.,
+//   Library/Java/JavaVirtualMachines/openjdk-21.jdk/Contents/Home.
+func findJavaHome() -> String {
+  if let home = ProcessInfo.processInfo.environment["JAVA_HOME"] {
+    return home
+  }
+
+  // This is a workaround for envs (some IDEs) which have trouble with
+  // picking up env variables during the build process
+  let path = "\(FileManager.default.homeDirectoryForCurrentUser.path()).java_home"
+  if let home = try? String(contentsOfFile: path, encoding: .utf8) {
+    if let lastChar = home.last, lastChar.isNewline {
+      return String(home.dropLast())
+    }
+
+    return home
+  }
+
+  fatalError("Please set the JAVA_HOME environment variable to point to where Java is installed.")
+}
+let javaHome = findJavaHome()
+
+let javaIncludePath = "\(javaHome)/include"
+#if os(Linux)
+  let javaPlatformIncludePath = "\(javaIncludePath)/linux"
+#elseif os(macOS)
+  let javaPlatformIncludePath = "\(javaIncludePath)/darwin"
+#else
+  // TODO: Handle windows as well
+  #error("Currently only macOS and Linux platforms are supported, this may change in the future.")
+#endif
+
+let package = Package(
+    name: "JExtractPluginSampleApp",
+    platforms: [
+        .macOS(.v10_15),
+    ],
+   products: [
+     .library(
+       name: "JExtractPluginSampleLib",
+       type: .dynamic,
+       targets: ["JExtractPluginSampleLib"]
+     ),
+   ],
+   dependencies: [
+        .package(name: "swift-java", path: "../../"),
+    ],
+    targets: [
+        .target(
+            name: "JExtractPluginSampleLib",
+            dependencies: [
+            ],
+            swiftSettings: [
+              .unsafeFlags(["-I\(javaIncludePath)", "-I\(javaPlatformIncludePath)"])
+            ],
+            plugins: [
+              .plugin(name: "JExtractSwiftPlugin", package: "swift-java"),
+            ]
+        ),
+    ]
+)

Samples/JExtractPluginSampleApp/Sources/JExtractPluginSampleLib/JExtractSwift.config

@@ -0,0 +1,3 @@
+{
+  "javaPackage": "com.example.swift"
+}

Samples/JExtractPluginSampleApp/Sources/JExtractPluginSampleLib/MyCoolSwiftClass.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
+//
+//===----------------------------------------------------------------------===//
+
+public class MyCoolSwiftClass {
+  var number: Int
+  public init(number: Int) {
+    print("[swift] init(number: \(number))")
+    self.number = number
+  }
+
+  public func exposedToJava() {
+    print("[swift] exposedToJava()")
+    print("[swift]   number = \(number)")
+  }
+}