tuned signature;

--- a/src/Pure/Admin/build_history.scala	Wed Nov 11 21:00:14 2020 +0100
+++ b/src/Pure/Admin/build_history.scala	Wed Nov 11 21:04:22 2020 +0100
@@ -358,8 +358,8 @@
             else None
           })
 
-      build_out_progress.echo("Writing log file " + log_path.ext("xz") + " ...")
-      File.write_xz(log_path.ext("xz"),
+      build_out_progress.echo("Writing log file " + log_path.xz + " ...")
+      File.write_xz(log_path.xz,
         terminate_lines(
           Protocol.Meta_Info_Marker(meta_info) :: build_result.out_lines :::
           session_build_info :::
@@ -377,7 +377,7 @@
 
       first_build = false
 
-      (build_result, log_path.ext("xz"))
+      (build_result, log_path.xz)
     }
   }
 

--- a/src/Pure/Admin/jenkins.scala	Wed Nov 11 21:00:14 2020 +0100
+++ b/src/Pure/Admin/jenkins.scala	Wed Nov 11 21:04:22 2020 +0100
@@ -99,7 +99,7 @@
     def download_log(store: Sessions.Store, dir: Path, progress: Progress = new Progress)
     {
       val log_dir = dir + Build_Log.log_subdir(date)
-      val log_path = log_dir + log_filename.ext("xz")
+      val log_path = log_dir + log_filename.xz
 
       if (!log_path.is_file) {
         progress.echo(log_path.expand.implode)

--- a/src/Pure/General/path.scala	Wed Nov 11 21:00:14 2020 +0100
+++ b/src/Pure/General/path.scala	Wed Nov 11 21:04:22 2020 +0100
@@ -193,6 +193,7 @@
       prfx + Path.basic(s + "." + e)
     }
 
+  def xz: Path = ext("xz")
   def tex: Path = ext("tex")
   def pdf: Path = ext("pdf")