JavaCompilerPlugin.swift

//===----------------------------------------------------------------------===//
//
// 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 JavaCompilerBuildToolPlugin: BuildToolPlugin {
  func createBuildCommands(context: PluginContext, target: Target) throws -> [Command] {
    guard let sourceModule = target.sourceModule else { return [] }

    // Collect all of the Java source files within this target's sources.
    let javaFiles = sourceModule.sourceFiles.map { $0.url }.filter {
      $0.pathExtension == "java"
    }
    if javaFiles.isEmpty {
      return []
    }

    // Note: Target doesn't have a directoryURL counterpart to directory,
    // so we cannot eliminate this deprecation warning.
    let sourceDir = target.directoryURL

    // The name of the configuration file SwiftJava.config from the target for
    // which we are generating Swift wrappers for Java classes.
    let configFile = sourceDir.appending(path: "swift-java.config")
    let config: Configuration?

    if let configData = try? Data(contentsOf: configFile) {
      let decoder = JSONDecoder()
      decoder.allowsJSON5 = true
      config = try? decoder.decode(Configuration.self, from: configData)
    } else {
      config = nil
    }

    // The class files themselves will be generated into the build directory
    // for this target.
    let classFiles = javaFiles.compactMap { sourceFileURL in
      guard sourceFileURL.isFileURL else {
        return nil as URL?
      }

      let sourceFilePath = sourceFileURL.path
      let sourceDirPath = sourceDir.path
      guard sourceFilePath.starts(with: sourceDirPath) else {
        fatalError("Could not get relative path for source file \(sourceFilePath)")
      }

      return URL(filePath: context.pluginWorkDirectoryURL.path)
        .appending(path: "Java")
        .appending(path: String(sourceFilePath.dropFirst(sourceDirPath.count)))
        .deletingPathExtension()
        .appendingPathExtension("class")
    }

    let javaHome = URL(filePath: findJavaHome())
    let javaClassFileURL = context.pluginWorkDirectoryURL
      .appending(path: "Java")
    #if os(Windows)
    let javac = "javac.exe"
    #else
    let javac = "javac"
    #endif
    return [
      .buildCommand(
        displayName: "Compiling \(javaFiles.count) Java files for target \(sourceModule.name) to \(javaClassFileURL)",
        executable:
          javaHome
          .appending(path: "bin")
          .appending(path: javac),
        arguments: javaFiles.map { $0.path } + [
          "-d", javaClassFileURL.path,
          "-parameters", // keep parameter names, which allows us to emit them in generated Swift decls
        ] + (config?.compilerVersionArgs ?? []),
        inputFiles: javaFiles,
        outputFiles: classFiles // FIXME: this is not quite enough, javac may generate more files for closures etc, which we don't know about unless we compile first
      )
    ]
  }
}