diff --git a/src/Pure/Tools/scala_project.scala b/src/Pure/Tools/scala_project.scala
--- a/src/Pure/Tools/scala_project.scala
+++ b/src/Pure/Tools/scala_project.scala
@@ -1,238 +1,238 @@
 /*  Title:      Pure/Tools/scala_project.scala
     Author:     Makarius
 
 Manage Isabelle/Scala/Java project sources, with output to Maven for
 IntelliJ IDEA.
 */
 
 package isabelle
 
 
 object Scala_Project
 {
   /* Maven project */
 
-  def java_version: String = "11"
+  def java_version: String = "15"
   def scala_version: String = scala.util.Properties.versionNumberString
 
   def maven_project(jars: List[Path]): String =
   {
     def dependency(jar: Path): String =
     {
       val name = jar.expand.drop_ext.base.implode
       val system_path = File.platform_path(jar.absolute)
       """  <dependency>
     <groupId>classpath</groupId>
     <artifactId>""" + XML.text(name) + """</artifactId>
     <version>0</version>
     <scope>system</scope>
     <systemPath>""" + XML.text(system_path) + """</systemPath>
   </dependency>"""
     }
 
     """<?xml version="1.0" encoding="UTF-8"?>
 <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
   xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
   <modelVersion>4.0.0</modelVersion>
 
   <groupId>isabelle</groupId>
   <artifactId>isabelle</artifactId>
   <version>0</version>
 
   <properties>
     <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
     <maven.compiler.source>""" + java_version + """</maven.compiler.source>
     <maven.compiler.target>""" + java_version + """</maven.compiler.target>
   </properties>
 
   <build>
     <plugins>
       <plugin>
         <groupId>net.alchim31.maven</groupId>
         <artifactId>scala-maven-plugin</artifactId>
         <version>4.5.3</version>
         <configuration>
             <scalaVersion>""" + scala_version + """</scalaVersion>
         </configuration>
         </plugin>
     </plugins>
   </build>
 
   <dependencies>""" + jars.map(dependency).mkString("\n", "\n", "\n") + """</dependencies>
 </project>"""
   }
 
 
   /* plugins: modules with dynamic build */
 
   class Plugin(dir: Path) extends Isabelle_System.Service
   {
     def context(): Scala_Build.Context = Scala_Build.context(dir)
   }
 
   lazy val plugins: List[Plugin] = Isabelle_System.make_services(classOf[Plugin])
 
 
   /* file and directories */
 
   lazy val isabelle_files: (List[Path], List[Path]) =
   {
     val contexts = Scala_Build.component_contexts() ::: plugins.map(_.context())
 
     val jars1 = Path.split(Isabelle_System.getenv("ISABELLE_CLASSPATH"))
     val jars2 = contexts.flatMap(_.requirements)
 
     val jars =
       Library.distinct(jars1 ::: jars2).filterNot(path => contexts.exists(_.is_module(path)))
 
     val sources =
       (for {
         context <- contexts.iterator
         path <- context.sources.iterator
         if path.is_scala || path.is_java
       } yield path).toList
 
     (jars, sources)
   }
 
   lazy val isabelle_scala_files: Map[String, Path] =
   {
     val context = Scala_Build.context(Path.ISABELLE_HOME, component = true)
     context.sources.iterator.foldLeft(Map.empty[String, Path]) {
       case (map, path) =>
         if (path.is_scala) {
         val base = path.base.implode
           map.get(base) match {
             case None => map + (base -> path)
             case Some(path2) => error("Conflicting base names: " + path + " vs. " + path2)
           }
         }
         else map
     }
   }
 
 
   /* compile-time position */
 
   def here: Here =
   {
     val exn = new Exception
     exn.getStackTrace.toList match {
       case _ :: caller :: _ =>
         val name = proper_string(caller.getFileName).getOrElse("")
         val line = caller.getLineNumber
         new Here(name, line)
       case _ => new Here("", 0)
     }
   }
 
   class Here private[Scala_Project](name: String, line: Int)
   {
     override def toString: String = name + ":" + line
     def position: Position.T =
       isabelle_scala_files.get(name) match {
         case Some(path) => Position.Line_File(line, path.implode)
         case None => Position.none
       }
   }
 
 
   /* scala project */
 
   val default_project_dir = Path.explode("$ISABELLE_HOME_USER/scala_project")
 
   def package_name(source_file: Path): Option[String] =
   {
     val lines = split_lines(File.read(source_file))
     val Package = """\s*\bpackage\b\s*(?:object\b\s*)?((?:\w|\.)+)\b.*""".r
     lines.collectFirst({ case Package(name) => name })
   }
 
   def the_package_dir(source_file: Path): Path =
   {
     package_name(source_file) match {
       case Some(name) =>
         if (source_file.is_java) Path.explode(space_explode('.', name).mkString("/"))
         else Path.basic(name)
       case None => error("Failed to guess package from " + source_file)
     }
   }
 
   def scala_project(
     project_dir: Path = default_project_dir,
     more_sources: List[Path] = Nil,
     symlinks: Boolean = false,
     force: Boolean = false,
     progress: Progress = new Progress): Unit =
   {
     if (project_dir.file.exists) {
       val detect =
         project_dir.is_dir &&
         (project_dir + Path.explode("pom.xml")).is_file &&
         (project_dir + Path.explode("src/main/scala")).is_dir
 
       if (force && detect) {
         progress.echo("Purging existing project directory: " + project_dir.absolute)
         Isabelle_System.rm_tree(project_dir)
       }
       else error("Project directory already exists: " + project_dir.absolute)
     }
 
     progress.echo("Creating project directory: " + project_dir.absolute)
     Isabelle_System.make_directory(project_dir)
 
     val java_src_dir = Isabelle_System.make_directory(Path.explode("src/main/java"))
     val scala_src_dir = Isabelle_System.make_directory(Path.explode("src/main/scala"))
 
     val (jars, sources) = isabelle_files
     isabelle_scala_files
 
     File.write(project_dir + Path.explode("pom.xml"), maven_project(jars))
 
     for (source <- sources ::: more_sources) {
       val dir = (if (source.is_java) java_src_dir else scala_src_dir) + the_package_dir(source)
       val target_dir = project_dir + dir
       if (!target_dir.is_dir) {
         progress.echo("  Creating package directory: " + dir)
         Isabelle_System.make_directory(target_dir)
       }
       if (symlinks) Isabelle_System.symlink(source.absolute, target_dir, native = true)
       else Isabelle_System.copy_file(source, target_dir)
     }
   }
 
 
   /* Isabelle tool wrapper */
 
   val isabelle_tool =
     Isabelle_Tool("scala_project", "setup Maven project for Isabelle/Scala/jEdit",
       Scala_Project.here, args =>
     {
       var project_dir = default_project_dir
       var symlinks = false
       var force = false
 
       val getopts = Getopts("""
 Usage: isabelle scala_project [OPTIONS] [MORE_SOURCES ...]
 
   Options are:
     -D DIR       project directory (default: """ + default_project_dir + """)
     -L           make symlinks to original source files
     -f           force update of existing directory
 
   Setup Maven project for Isabelle/Scala/jEdit --- to support common IDEs
   such as IntelliJ IDEA.
 """,
         "D:" -> (arg => project_dir = Path.explode(arg)),
         "L" -> (_ => symlinks = true),
         "f" -> (_ => force = true))
 
       val more_args = getopts(args)
 
       val more_sources = more_args.map(Path.explode)
       val progress = new Console_Progress
 
       scala_project(project_dir = project_dir, more_sources = more_sources,
         symlinks = symlinks, force = force, progress = progress)
     })
 }