ENH: add a linkcode extension

doc/ext/linkcode.rst

@@ -0,0 +1,47 @@
+:mod:`sphinx.ext.linkcode` -- Add external links to source code
+===============================================================
+
+.. module:: sphinx.ext.linkcode
+   :synopsis: Add external links to source code.
+.. moduleauthor:: Pauli Virtanen
+
+.. versionadded:: 1.1
+
+This extension looks at your Python object descriptions
+(``.. class::``, ``.. function::`` etc.) and adds external links to
+code hosted somewhere on the web. The intent is similar to the
+``sphinx.ext.viewcode`` extension, but assumes the source code can be
+found somewhere on the Internet.
+
+In your configuration, you need to specify a :confval:`linkcode_resolve` 
+function that returns an URL based on the name of a module and 
+the full name of the object.
+
+.. confval:: linkcode_resolve
+
+   This is a function ``linkcode_resolve(domain, info)``,
+   which should return the URL to source code corresponding to
+   the object in given domain with given information. 
+
+   The function should return ``None`` if no link is to be added.
+
+   The argument ``domain`` specifies the language domain the object is
+   in. ``info`` is a dictionary with the following keys guaranteed to
+   be present (dependent on the domain):
+
+   - ``c``: ``names`` (list of names for the object)
+   - ``cpp``: ``names`` (list of names for the object)
+   - ``py``: ``module`` (name of the module), ``fullname`` (name of the object)
+   - ``javascript``: ``object`` (name of the object), ``fullname`` (name of the item)
+
+   Example:
+
+   .. code-block:: python
+
+      def linkcode_resolve(domain, info):
+          if domain != 'py':
+              return None
+	  if not info['module']:
+	      return None
+	  filename = info['module'].replace('.', '/')
+          return "http://somesite/sourcerepo/%s.py" % filename

doc/extensions.rst

@@ -53,6 +53,7 @@ These extensions are built in and can be activated by respective entries in the
    ext/todo
    ext/extlinks
    ext/viewcode
+   ext/linkcode
    ext/oldcmarkup