Use @registrar.command where available (hg 3.7+).
    
        | author | Kevin Bullock <kbullock@ringworld.org> | 
    
        | date | Fri, 20 Oct 2017 10:51:53 -0500 | 
    
    
        | parents | 5334581e231a | 
    
        | children | dc481ce24b60 | 
    
        | branches/tags | (none) | 
    
        | files | prompt.py | 
Changes
    
--- a/prompt.py	Wed Oct 05 20:52:29 2016 +0000
+++ b/prompt.py	Fri Oct 20 10:51:53 2017 -0500
@@ -20,8 +20,13 @@
 from mercurial.i18n import _
 from mercurial.node import hex, short
 
+# command registration moved into `registrar` module in v3.7.
 cmdtable = {}
-command = cmdutil.command(cmdtable)
+try:
+    from mercurial import registrar
+    command = registrar.command(cmdtable)
+except ImportError:
+    command = cmdutil.command(cmdtable)
 
 # `revrange' has been moved into module `scmutil' since v1.9.
 try :