diff -r e48d93811ed7 -r 04bce3478688 src/Pure/Tools/scala_project.scala
--- a/src/Pure/Tools/scala_project.scala	Mon Oct 05 21:15:58 2020 +0200
+++ b/src/Pure/Tools/scala_project.scala	Mon Oct 05 22:07:25 2020 +0200
@@ -73,8 +73,7 @@
 
     val src_dir = project_dir + Path.explode("src/main/scala")
     val java_src_dir = project_dir + Path.explode("src/main/java")
-    val scala_src_dir = project_dir + Path.explode("src/main/scala")
-    Isabelle_System.make_directory(scala_src_dir)
+    val scala_src_dir = Isabelle_System.make_directory(project_dir + Path.explode("src/main/scala"))
 
     Isabelle_System.copy_dir(Path.explode("~~/src/Tools/jEdit/dist/jEdit"), java_src_dir)