new file mode 100644
--- /dev/null
+++ b/hgext/alias.py
@@ -0,0 +1,78 @@
+# Copyright (C) 2007 Brendan Cully <brendan@kublai.com>
+# This file is published under the GNU GPL.
+
+'''allow user-defined command aliases
+
+To use, create entries in your hgrc of the form
+
+[alias]
+mycmd = cmd --args
+'''
+
+from mercurial.cmdutil import findcmd, UnknownCommand, AmbiguousCommand
+from mercurial import commands
+
+cmdtable = {}
+
+class RecursiveCommand(Exception): pass
+
+class lazycommand(object):
+    '''defer command lookup until needed, so that extensions loaded
+    after alias can be aliased'''
+    def __init__(self, ui, name, target):
+        self._ui = ui
+        self._name = name
+        self._target = target
+        self._cmd = None
+
+    def __len__(self):
+        self._resolve()
+        return len(self._cmd)
+
+    def __getitem__(self, key):
+        self._resolve()
+        return self._cmd[key]
+
+    def __iter__(self):
+        self._resolve()
+        return self._cmd.__iter__()
+
+    def _resolve(self):
+        if self._cmd is not None:
+            return
+
+        try:
+            self._loading = True
+            self._cmd = findcmd(self._ui, self._target)[1]
+            if self._cmd == self:
+                raise RecursiveCommand()
+            if self._target in commands.norepo.split(' '):
+                commands.norepo += ' %s' % self._name
+            return
+        except UnknownCommand:
+            msg = '*** [alias] %s: command %s is unknown' % \
+                  (self._name, self._target)
+        except AmbiguousCommand:
+            msg = '*** [alias] %s: command %s is ambiguous' % \
+                  (self._name, self._target)
+        except RecursiveCommand:
+            msg = '*** [alias] %s: circular dependency on %s' % \
+                  (self._name, self._target)
+        def nocmd(*args, **opts):
+            self._ui.warn(msg + '\n')
+            return 1
+        nocmd.__doc__ = msg
+        self._cmd = (nocmd, [], '')
+        commands.norepo += ' %s' % self._name
+
+def uisetup(ui):
+    for cmd, target in ui.configitems('alias'):
+        if not target:
+            ui.warn('*** [alias] %s: no definition\n' % cmd)
+            continue
+        args = target.split(' ')
+        tcmd = args.pop(0)
+        if args:
+            pui = ui.parentui or ui
+            pui.setconfig('defaults', cmd, ' '.join(args))
+        cmdtable[cmd] = lazycommand(ui, cmd, tcmd)

new file mode 100755
--- /dev/null
+++ b/tests/test-alias
@@ -0,0 +1,32 @@
+#!/bin/sh
+
+cat > $HGRCPATH <<EOF
+[extensions]
+alias=
+
+[alias]
+myinit = init
+cleanstatus = status -c
+unknown = bargle
+ambiguous = s
+recursive = recursive
+EOF
+
+echo '% basic'
+hg myinit alias
+
+echo '% unknown'
+hg unknown
+
+echo '% ambiguous'
+hg ambiguous
+
+echo '% recursive'
+hg recursive
+
+cd alias
+echo foo > foo
+hg ci -Amfoo
+
+echo '% with opts'
+hg cleanst

new file mode 100644
--- /dev/null
+++ b/tests/test-alias.out
@@ -0,0 +1,10 @@
+% basic
+% unknown
+*** [alias] unknown: command bargle is unknown
+% ambiguous
+*** [alias] ambiguous: command s is ambiguous
+% recursive
+*** [alias] recursive: circular dependency on recursive
+adding foo
+% with opts
+C foo