--- a/mercurial/hook.py	Tue Dec 28 13:31:30 2010 -0600
+++ b/mercurial/hook.py	Fri Dec 24 15:22:00 2010 +0100
@@ -92,6 +92,12 @@
     for k, v in args.iteritems():
         if hasattr(v, '__call__'):
             v = v()
+        if isinstance(v, dict):
+            # make the dictionary element order stable across Python
+            # implementations
+            v = ('{' +
+                 ', '.join('%r: %r' % i for i in sorted(v.iteritems())) +
+                 '}')
         env['HG_' + k.upper()] = v
 
     if repo:

--- a/tests/test-hook.t	Tue Dec 28 13:31:30 2010 -0600
+++ b/tests/test-hook.t	Fri Dec 24 15:22:00 2010 +0100
@@ -68,13 +68,13 @@
 test generic hooks
 
   $ hg id
-  pre-identify hook: HG_ARGS=id HG_OPTS={'tags': None, 'rev': '', 'num': None, 'branch': None, 'id': None} HG_PATS=[] 
+  pre-identify hook: HG_ARGS=id HG_OPTS={'branch': None, 'id': None, 'num': None, 'rev': '', 'tags': None} HG_PATS=[] 
   warning: pre-identify hook exited with status 1
   [1]
   $ hg cat b
-  pre-cat hook: HG_ARGS=cat b HG_OPTS={'rev': '', 'decode': None, 'exclude': [], 'output': '', 'include': []} HG_PATS=['b'] 
+  pre-cat hook: HG_ARGS=cat b HG_OPTS={'decode': None, 'exclude': [], 'include': [], 'output': '', 'rev': ''} HG_PATS=['b'] 
   b
-  post-cat hook: HG_ARGS=cat b HG_OPTS={'rev': '', 'decode': None, 'exclude': [], 'output': '', 'include': []} HG_PATS=['b'] HG_RESULT=0 
+  post-cat hook: HG_ARGS=cat b HG_OPTS={'decode': None, 'exclude': [], 'include': [], 'output': '', 'rev': ''} HG_PATS=['b'] HG_RESULT=0 
 
   $ cd ../b
   $ hg pull ../a