diff -r 06080afd0565 -r c04e0836f039 mercurial/archival.py
--- a/mercurial/archival.py	Sun Sep 15 22:43:32 2019 +0900
+++ b/mercurial/archival.py	Tue Sep 17 10:47:31 2019 +0000
@@ -67,6 +67,7 @@
     'tbz2': ['.tbz2', '.tar.bz2'],
     'tgz': ['.tgz', '.tar.gz'],
     'zip': ['.zip'],
+    'txz': ['.txz', '.tar.xz']
     }
 
 def guesskind(dest):
@@ -270,6 +271,7 @@
     'tar': tarit,
     'tbz2': lambda name, mtime: tarit(name, mtime, 'bz2'),
     'tgz': lambda name, mtime: tarit(name, mtime, 'gz'),
+    'txz': lambda name, mtime: tarit(name, mtime, 'xz'),
     'uzip': lambda name, mtime: zipit(name, mtime, False),
     'zip': zipit,
     }
@@ -295,6 +297,9 @@
     subrepos tells whether to include subrepos.
     '''
 
+    if kind == 'txz' and not pycompat.ispy3:
+        raise error.Abort(_('xz compression is only available in Python 3'))
+
     if kind == 'files':
         if prefix:
             raise error.Abort(_('cannot give prefix when archiving to files'))