Moar constructive (#28254)

* made composite vars and groups generic

now you can do both in every plugin that chooses to suport it
renamed constructed_groups as it now also constructs vars ... to constructed
moved most of constructed_groups logic into base class to easily share

* documented inventory_hostname

* typo fix

lib/ansible/plugins/inventory/constructed.py

@@ -0,0 +1,116 @@
+# Copyright 2017 RedHat, inc
+#
+# This file is part of Ansible
+#
+# Ansible is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# Ansible is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with Ansible.  If not, see <http://www.gnu.org/licenses/>.
+#############################################
+'''
+DOCUMENTATION:
+    name: constructed
+    plugin_type: inventory
+    version_added: "2.4"
+    short_description: Uses Jinja2 to construct vars and groups based on existing inventory.
+    description:
+        - Uses a YAML configuration file to define var expresisions and group conditionals
+        - The Jinja2 conditionals that qualify a host for membership.
+        - The JInja2 exprpessions are calculated and assigned to the variables
+        - Only variables already available from previous inventories can be used for templating.
+        - Failed expressions will be ignored (assumes vars were missing).
+    compose:
+        description: create vars from jinja2 expressions
+        type: dictionary
+        default: {}
+    groups:
+        description: add hosts to group based on Jinja2 conditionals
+        type: dictionary
+        default: {}
+EXAMPLES: | # inventory.config file in YAML format
+    plugin: comstructed
+    compose:
+        var_sum: var1 + var2
+    groups:
+        # simple name matching
+        webservers: inventory_hostname.startswith('web')
+
+        # using ec2 'tags' (assumes aws inventory)
+        development: "'devel' in (ec2_tags|list)"
+
+        # using other host properties populated in inventory
+        private_only: not (public_dns_name is defined or ip_address is defined)
+
+        # complex group membership
+        multi_group: (group_names|intersection(['alpha', 'beta', 'omega']))|length >= 2
+'''
+
+from __future__ import (absolute_import, division, print_function)
+__metaclass__ = type
+
+import os
+
+from ansible.errors import AnsibleParserError
+from ansible.plugins.inventory import BaseInventoryPlugin
+from ansible.module_utils._text import to_native
+from ansible.utils.vars import combine_vars
+
+
+class InventoryModule(BaseInventoryPlugin):
+    """ constructs groups and vars using Jinaj2 template expressions """
+
+    NAME = 'constructed'
+
+    def __init__(self):
+
+        super(InventoryModule, self).__init__()
+
+    def verify_file(self, path):
+
+        valid = False
+        if super(InventoryModule, self).verify_file(path):
+            file_name, ext = os.path.splitext(path)
+
+            if not ext or ext == '.config':
+                valid = True
+
+        return valid
+
+    def parse(self, inventory, loader, path, cache=False):
+        ''' parses the inventory file '''
+
+        super(InventoryModule, self).parse(inventory, loader, path, cache=True)
+
+        try:
+            data = self.loader.load_from_file(path)
+        except Exception as e:
+            raise AnsibleParserError("Unable to parse %s: %s" % (to_native(path), to_native(e)))
+
+        if not data or data.get('plugin') != self.NAME:
+            raise AnsibleParserError("%s is empty or not a constructed groups config file" % (to_native(path)))
+
+        try:
+            # Go over hosts (less var copies)
+            for host in inventory.hosts:
+
+                # get available variables to templar
+                hostvars = inventory.hosts[host].get_vars()
+                if host in inventory.cache:  # adds facts if cache is active
+                    hostvars = combine_vars(hostvars, inventory.cache[host])
+
+                # create composite vars
+                self._set_composite_vars(data.get('compose'), hostvars, host)
+
+                # constructed groups based on conditionals
+                self._add_host_to_composed_groups(data.get('groups'), hostvars, host)
+
+        except Exception as e:
+            raise AnsibleParserError("failed to parse %s: %s " % (to_native(path), to_native(e)))