extensions: allow extending command synopsis and docstring

Mercurial uses a synopsis string and the docstring of a command for the
command's help output. Today  there is no way for an extension that adds
functionality to a command to extend either of these help strings.

This patch enables appending to both the doctring and the synopsis, and adds
a test for this functionality. Example usage is shown in the test and is also
described in the docstring of extensions.wrapcommand().

mercurial/extensions.py

@@ -152,7 +152,7 def afterloaded(extension, callback):
     else:
         _aftercallbacks.setdefault(extension, []).append(callback)
 
-def wrapcommand(table, command, wrapper):
+def wrapcommand(table, command, wrapper, synopsis=None, docstring=None):
     '''Wrap the command named `command' in table
 
     Replace command in the command table with wrapper. The wrapped command will
@@ -164,6 +164,22 def wrapcommand(table, command, wrapper)
 
     where orig is the original (wrapped) function, and *args, **kwargs
     are the arguments passed to it.
+
+    Optionally append to the command synopsis and docstring, used for help.
+    For example, if your extension wraps the ``bookmarks`` command to add the
+    flags ``--remote`` and ``--all`` you might call this function like so:
+
+      synopsis = ' [-a] [--remote]'
+      docstring = """
+
+      The ``remotenames`` extension adds the ``--remote`` and ``--all`` (``-a``)
+      flags to the bookmarks command. Either flag will show the remote bookmarks
+      known to the repository; ``--remote`` will also supress the output of the
+      local bookmarks.
+      """
+
+      extensions.wrapcommand(commands.table, 'bookmarks', exbookmarks,
+                             synopsis, docstring)
     '''
     assert callable(wrapper)
     aliases, entry = cmdutil.findcmd(command, table)
@@ -177,11 +193,17 def wrapcommand(table, command, wrapper)
         return util.checksignature(wrapper)(
             util.checksignature(origfn), *args, **kwargs)
 
-    wrap.__doc__ = getattr(origfn, '__doc__')
     wrap.__module__ = getattr(origfn, '__module__')
 
+    doc = getattr(origfn, '__doc__')
+    if docstring is not None:
+        doc += docstring
+    wrap.__doc__ = doc
+
     newentry = list(entry)
     newentry[0] = wrap
+    if synopsis is not None:
+        newentry[2] += synopsis
     table[key] = tuple(newentry)
     return entry
 

tests/test-extension.t

@@ -1140,3 +1140,27 disabling in command line overlays with
   C sub3/3
 
   $ cd ..
+
+Test synopsis and docstring extending
+
+  $ hg init exthelp
+  $ cat > exthelp.py <<EOF
+  > from mercurial import commands, extensions
+  > def exbookmarks(orig, *args, **opts):
+  >     return orig(*args, **opts)
+  > def uisetup(ui):
+  >     synopsis = ' GREPME [--foo] [-x]'
+  >     docstring = '''
+  >     GREPME make sure that this is in the help!
+  >     '''
+  >     extensions.wrapcommand(commands.table, 'bookmarks', exbookmarks,
+  >                            synopsis, docstring)
+  > EOF
+  $ abspath=`pwd`/exthelp.py
+  $ echo '[extensions]' >> $HGRCPATH
+  $ echo "exthelp = $abspath" >> $HGRCPATH
+  $ cd exthelp
+  $ hg help bookmarks | grep GREPME
+  hg bookmarks [OPTIONS]... [NAME]... GREPME [--foo] [-x]
+      GREPME make sure that this is in the help!
+