src/Pure/General/file.scala

   {
     if (Platform.is_windows) Isabelle_System.bash("test -x " + bash_path(path)).check.ok
     else path.file.canExecute
   }
 
-  def executable(path: Path)
-  {
-    if (Platform.is_windows) Isabelle_System.bash("chmod a+x " + bash_path(path)).check
-    else path.file.setExecutable(true, false)
+  def set_executable(path: Path, flag: Boolean)
+  {
+    if (Platform.is_windows && flag) Isabelle_System.bash("chmod a+x " + bash_path(path)).check
+    else if (Platform.is_windows) Isabelle_System.bash("chmod a-x " + bash_path(path)).check
+    else path.file.setExecutable(flag, false)
   }
 }