namespaces: add a function to turn single results into lists

mercurial/namespaces.py

@@ -1,40 +1,49 b''
 from mercurial import util
 
+def tolist(val):
+    """
+    a convenience method to return an empty list instead of None
+    """
+    if val is None:
+        return []
+    else:
+        return [val]
+
 class namespaces(object):
     """
     provides an interface to register a generic many-to-many mapping between
     some (namespaced) names and nodes. The goal here is to control the
     pollution of jamming things into tags or bookmarks (in extension-land) and
     to simplify internal bits of mercurial: log output, tab completion, etc.
 
     More precisely, we define a list of names (the namespace) and  a mapping of
     names to nodes. This name mapping returns a list of nodes.
 
     Furthermore, each name mapping will be passed a name to lookup which might
     not be in its domain. In this case, each method should return an empty list
     and not raise an error.
 
     We'll have a dictionary '_names' where each key is a namespace and
     its value is a dictionary of functions:
       'namemap': function that takes a name and returns a list of nodes
     """
 
     _names_version = 0
 
     def __init__(self):
         self._names = util.sortdict()
 
     def addnamespace(self, namespace, namemap, order=None):
         """
         register a namespace
 
         namespace: the name to be registered (in plural form)
         namemap: function that inputs a node, output name(s)
         order: optional argument to specify the order of namespaces
                (e.g. 'branches' should be listed before 'bookmarks')
         """
         val = {'namemap': namemap}
         if order is not None:
             self._names.insert(order, namespace, val)
         else:
             self._names[namespace] = val