[PATCH 1 of 5] summary: augment output with info from extensions

[Bryan O'Sullivan]

# HG changeset patch
# User Bryan O'Sullivan <bryano at fb.com>
# Date 1368555795 25200
#      Tue May 14 11:23:15 2013 -0700
# Node ID 50703ffc65cfec6e37f31c74da5e2acf22c9ac08
# Parent  d77922fd8798acbf6daa0435eb7a7b1c13e3918b
summary: augment output with info from extensions

diff --git a/mercurial/cmdutil.py b/mercurial/cmdutil.py
--- a/mercurial/cmdutil.py
+++ b/mercurial/cmdutil.py
@@ -2082,3 +2082,6 @@ def command(table):
         return decorator
 
     return cmd
+
+# a list of (ui, repo) functions called by commands.summary
+summaryhooks = util.hooks()
diff --git a/mercurial/commands.py b/mercurial/commands.py
--- a/mercurial/commands.py
+++ b/mercurial/commands.py
@@ -5485,6 +5485,8 @@ def summary(ui, repo, **opts):
         ui.write(_('update: %d new changesets, %d branch heads (merge)\n') %
                  (new, len(bheads)))
 
+    cmdutil.summaryhooks(ui, repo)
+
     if opts.get('remote'):
         t = []
         source, branches = hg.parseurl(ui.expandpath('default'))
diff --git a/mercurial/util.py b/mercurial/util.py
--- a/mercurial/util.py
+++ b/mercurial/util.py
@@ -1946,3 +1946,19 @@ def sizetoint(s):
         return int(t)
     except ValueError:
         raise error.ParseError(_("couldn't parse size: %s") % s)
+
+class hooks(object):
+    '''A collection of hook functions that can be used to extend a
+    function's behaviour. Hooks are called in lexicographic order,
+    based on the names of their sources.'''
+
+    def __init__(self):
+        self._hooks = []
+
+    def add(self, source, hook):
+        self._hooks.append((source, hook))
+
+    def __call__(self, *args):
+        self._hooks.sort(key=lambda x: x[0])
+        for source, hook in self._hooks:
+            hook(*args)