Enable autoloading of inventory plugins (#32709)

* Automatically loads and executes an inventory plugin specified by a standard YAML inventory config file containing a `plugin` key at its root.
* Moved inventory PluginLoader to a shared global instance.

lib/ansible/cli/doc.py

@@ -29,7 +29,7 @@ from ansible.module_utils._text import to_native
 from ansible.module_utils.six import string_types
 from ansible.parsing.yaml.dumper import AnsibleDumper
 from ansible.plugins.loader import module_loader, action_loader, lookup_loader, callback_loader, cache_loader, \
-    vars_loader, connection_loader, strategy_loader, PluginLoader
+    vars_loader, connection_loader, strategy_loader, inventory_loader
 from ansible.utils import plugin_docs
 try:
     from __main__ import display
@@ -97,7 +97,7 @@ class DocCLI(CLI):
         elif plugin_type == 'vars':
             loader = vars_loader
         elif plugin_type == 'inventory':
-            loader = PluginLoader('InventoryModule', 'ansible.plugins.inventory', C.DEFAULT_INVENTORY_PLUGIN_PATH, 'inventory_plugins')
+            loader = inventory_loader
         else:
             loader = module_loader
 

lib/ansible/config/base.yml

@@ -1239,7 +1239,7 @@ HOST_KEY_CHECKING:
   type: boolean
 INVENTORY_ENABLED:
   name: Active Inventory plugins
-  default: ['host_list', 'script', 'yaml', 'ini']
+  default: ['host_list', 'script', 'yaml', 'ini', 'auto']
   description: List of enabled inventory plugins, it also determines the order in which they are used.
   env: [{name: ANSIBLE_INVENTORY_ENABLED}]
   ini:

lib/ansible/inventory/manager.py

@@ -30,7 +30,7 @@ from ansible.inventory.data import InventoryData
 from ansible.module_utils.six import string_types
 from ansible.module_utils._text import to_bytes, to_native, to_text
 from ansible.parsing.utils.addresses import parse_address
-from ansible.plugins.loader import PluginLoader
+from ansible.plugins.loader import inventory_loader
 from ansible.utils.path import unfrackpath
 
 try:
@@ -178,7 +178,6 @@ class InventoryManager(object):
     def _setup_inventory_plugins(self):
         ''' sets up loaded inventory plugins for usage '''
 
-        inventory_loader = PluginLoader('InventoryModule', 'ansible.plugins.inventory', C.DEFAULT_INVENTORY_PLUGIN_PATH, 'inventory_plugins')
         display.vvvv('setting up inventory plugins')
 
         for name in C.INVENTORY_ENABLED:

lib/ansible/plugins/inventory/auto.py

@@ -0,0 +1,56 @@
+# Copyright (c) 2017 Ansible Project
+# GNU General Public License v3.0+ (see COPYING or https://www.gnu.org/licenses/gpl-3.0.txt)
+
+from __future__ import (absolute_import, division, print_function)
+__metaclass__ = type
+
+DOCUMENTATION = '''
+    name: auto
+    plugin_type: inventory
+    authors:
+      - Matt Davis <@nitzmahone>
+    short_description: Loads and executes an inventory plugin specified in a YAML config
+    description:
+        - By whitelisting C(auto) as the final inventory plugin, any YAML inventory config file with a
+          C(plugin) key at its root will automatically cause the named plugin to be loaded and executed with that
+          config. This effectively provides automatic whitelisting of all installed/accessible inventory plugins.
+        - To disable this behavior, remove C(auto) from the C(INVENTORY_ENABLED) config element.
+    options:
+'''
+
+EXAMPLES = '''
+# This plugin is not intended for direct use; it is a fallback mechanism for automatic whitelisting of
+# all installed inventory plugins.
+'''
+
+from ansible.errors import AnsibleParserError
+from ansible.plugins.inventory import BaseInventoryPlugin
+from ansible.plugins.loader import inventory_loader
+
+
+class InventoryModule(BaseInventoryPlugin):
+
+    NAME = 'auto'
+
+    def verify_file(self, path):
+        if not path.endswith('.yml') and not path.endswith('.yaml'):
+            return False
+        return super(InventoryModule, self).verify_file(path)
+
+    def parse(self, inventory, loader, path, cache=True):
+        config_data = loader.load_from_file(path)
+
+        plugin_name = config_data.get('plugin')
+
+        if not plugin_name:
+            raise AnsibleParserError("no root 'plugin' key found, '{0}' is not a valid YAML inventory plugin config file".format(path))
+
+        plugin = inventory_loader.get(plugin_name)
+
+        if not plugin:
+            raise AnsibleParserError("inventory config '{0}' specifies unknown plugin '{1}'".format(path, plugin_name))
+
+        if not plugin.verify_file(path):
+            raise AnsibleParserError("inventory config '{0}' could not be verified by plugin '{1}'".format(path, plugin_name))
+
+        plugin.parse(inventory, loader, path, cache=cache)

lib/ansible/plugins/loader.py

@@ -582,3 +582,10 @@ netconf_loader = PluginLoader(
     'netconf_plugins',
     required_base_class='NetconfBase'
 )
+
+inventory_loader = PluginLoader(
+    'InventoryModule',
+    'ansible.plugins.inventory',
+    C.DEFAULT_INVENTORY_PLUGIN_PATH,
+    'inventory_plugins'
+)