Adds a decorator for registering jinja filters

The decorator adds the filter to a class attribute, `salt_jinja_filters`
that maps filter names to functions.

salt/utils/decorators/__init__.py

@@ -633,3 +633,28 @@ def ignores_kwargs(*kwarg_names):
             return fn(*args, **kwargs_filtered)
         return __ignores_kwargs
     return _ignores_kwargs
+
+
+class JinjaFilter(object):
+    '''
+    This decorator is used to specify that a function is to be loaded as a
+    Jinja filter.
+    '''
+    salt_jinja_filters = {}
+
+    def __init__(self, name=None):
+        '''
+        '''
+        self.name = name
+
+    def __call__(self, function):
+        '''
+        '''
+        name = self.name or function.__name__
+        if name not in self.salt_jinja_filters:
+            log.debug('Marking "{0}" as a jinja filter'.format(name))
+            self.salt_jinja_filters[name] = function
+        return function
+
+
+jinja_filter = JinjaFilter

salt/utils/templates.py

@@ -32,6 +32,7 @@ from salt.exceptions import (
 import salt.utils.jinja
 import salt.utils.network
 from salt.utils.odict import OrderedDict
+from salt.utils.decorators import JinjaFilter
 from salt import __path__ as saltpath
 
 log = logging.getLogger(__name__)
@@ -391,6 +392,8 @@ def render_jinja_tmpl(tmplstr, context, tmplpath=None):
     jinja_env.filters['network_hosts'] = salt.utils.network.network_hosts  # return the hosts within a network
     jinja_env.filters['network_size'] = salt.utils.network.network_size  # return the network size
 
+    jinja_env.filters.update(JinjaFilter.salt_jinja_filters)
+
     # globals
     jinja_env.globals['odict'] = OrderedDict
     jinja_env.globals['show_full_context'] = salt.utils.jinja.show_full_context