There can be only one localhost

The changes to exclude implicit localhosts from group patterns exposed
the bug that we sometimes create multiple implicit localhosts, which
caused some bugs with things like includes, where the host was used as
an entry into a dict, so having multiple meant that the incorrect host
(with a different uuid) was found and includes were not executed for
implicit localhosts.

lib/ansible/inventory/__init__.py

@@ -58,6 +58,7 @@ def __init__(self, loader, variable_manager, host_list=C.DEFAULT_HOST_LIST):
         self.host_list = host_list
         self._loader = loader
         self._variable_manager = variable_manager
+        self.localhost = None
 
         # caching to avoid repeated calculations, particularly with
         # external inventory scripts.
@@ -89,6 +90,8 @@ def __init__(self, loader, variable_manager, host_list=C.DEFAULT_HOST_LIST):
         self.clear_pattern_cache()
 
         self.parse_inventory(host_list)
+        if self.localhost is None:
+            self.localhost = self._create_implicit_localhost()
 
     def serialize(self):
         data = dict()
@@ -125,7 +128,13 @@ def parse_inventory(self, host_list):
                     display.vvv("Unable to parse address from hostname, leaving unchanged: %s" % to_unicode(e))
                     host = h
                     port = None
-                all.add_host(Host(host, port))
+                new_host = Host(host, port)
+                all.add_host(new_host)
+                if new_host.name in C.LOCALHOST:
+                    if self.localhost is None:
+                        self.localhost = new_host
+                    else:
+                        display.warning("A duplicate localhost-like entry was found (%s). First found localhost was %s" % (new_host.name, self.localhost.name))
         elif self._loader.path_exists(host_list):
             #TODO: switch this to a plugin loader and a 'condition' per plugin on which it should be tried, restoring 'inventory pllugins'
             if self.is_directory(host_list):
@@ -461,12 +470,9 @@ def __append_host_to_results(host):
                     for host in matching_hosts:
                         __append_host_to_results(host)
 
-        if pattern in C.LOCALHOST and len(results) == 0:
-            new_host = self._create_implicit_localhost(pattern)
-            results.append(new_host)
         return results
 
-    def _create_implicit_localhost(self, pattern):
+    def _create_implicit_localhost(self, pattern='localhost'):
         new_host = Host(pattern)
         new_host.address = "127.0.0.1"
         new_host.implicit = True
@@ -495,17 +501,11 @@ def get_groups(self):
     def get_host(self, hostname):
         if hostname not in self._hosts_cache:
             self._hosts_cache[hostname] = self._get_host(hostname)
-            if hostname in C.LOCALHOST:
-                for host in C.LOCALHOST.difference((hostname,)):
-                    self._hosts_cache[host] = self._hosts_cache[hostname]
         return self._hosts_cache[hostname]
 
     def _get_host(self, hostname):
-        if hostname in C.LOCALHOST:
-            for host in self.get_group('all').get_hosts():
-                if host.name in C.LOCALHOST:
-                    return host
-            return self._create_implicit_localhost(hostname)
+        if hostname in C.LOCALHOST and self.localhost:
+            self.localhost
         matching_host = None
         for group in self.groups.values():
             for host in group.get_hosts():