--- a/mercurial/wireproto.py	Fri Mar 02 18:50:49 2018 -0500
+++ b/mercurial/wireproto.py	Fri Mar 02 09:47:37 2018 -0500
@@ -592,9 +592,10 @@
 
 class commandentry(object):
     """Represents a declared wire protocol command."""
-    def __init__(self, func, args=''):
+    def __init__(self, func, args='', transports=None):
         self.func = func
         self.args = args
+        self.transports = transports or set()
 
     def _merge(self, func, args):
         """Merge this instance with an incoming 2-tuple.
@@ -604,7 +605,7 @@
         data not captured by the 2-tuple and a new instance containing
         the union of the two objects is returned.
         """
-        return commandentry(func, args=args)
+        return commandentry(func, args=args, transports=set(self.transports))
 
     # Old code treats instances as 2-tuples. So expose that interface.
     def __iter__(self):
@@ -640,7 +641,9 @@
             if k in self:
                 v = self[k]._merge(v[0], v[1])
             else:
-                v = commandentry(v[0], args=v[1])
+                # Use default values from @wireprotocommand.
+                v = commandentry(v[0], args=v[1],
+                                 transports=set(wireprototypes.TRANSPORTS))
         else:
             raise ValueError('command entries must be commandentry instances '
                              'or 2-tuples')
@@ -649,22 +652,52 @@
 
     def commandavailable(self, command, proto):
         """Determine if a command is available for the requested protocol."""
-        # For now, commands are available for all protocols. So do a simple
-        # membership test.
-        return command in self
+        assert proto.name in wireprototypes.TRANSPORTS
+
+        entry = self.get(command)
+
+        if not entry:
+            return False
+
+        if proto.name not in entry.transports:
+            return False
+
+        return True
+
+# Constants specifying which transports a wire protocol command should be
+# available on. For use with @wireprotocommand.
+POLICY_ALL = 'all'
+POLICY_V1_ONLY = 'v1-only'
+POLICY_V2_ONLY = 'v2-only'
 
 commands = commanddict()
 
-def wireprotocommand(name, args=''):
+def wireprotocommand(name, args='', transportpolicy=POLICY_ALL):
     """Decorator to declare a wire protocol command.
 
     ``name`` is the name of the wire protocol command being provided.
 
     ``args`` is a space-delimited list of named arguments that the command
     accepts. ``*`` is a special value that says to accept all arguments.
+
+    ``transportpolicy`` is a POLICY_* constant denoting which transports
+    this wire protocol command should be exposed to. By default, commands
+    are exposed to all wire protocol transports.
     """
+    if transportpolicy == POLICY_ALL:
+        transports = set(wireprototypes.TRANSPORTS)
+    elif transportpolicy == POLICY_V1_ONLY:
+        transports = {k for k, v in wireprototypes.TRANSPORTS.items()
+                      if v['version'] == 1}
+    elif transportpolicy == POLICY_V2_ONLY:
+        transports = {k for k, v in wireprototypes.TRANSPORTS.items()
+                      if v['version'] == 2}
+    else:
+        raise error.Abort(_('invalid transport policy value: %s') %
+                          transportpolicy)
+
     def register(func):
-        commands[name] = commandentry(func, args=args)
+        commands[name] = commandentry(func, args=args, transports=transports)
         return func
     return register