Make add_host be idempotent/show changed status (#69897)

Change:
- The `add_host` action now shows an accurate change status.

Test Plan:
- Added a plethora of integration tests.

Tickets:
Fixes #69881

Signed-off-by: Rick Elrod <rick@elrod.me>

changelogs/fragments/69881-add_host-show-changed.yml

@@ -0,0 +1,2 @@
+bugfixes:
+  - add_host action now correctly shows idempotency/changed status

lib/ansible/plugins/action/add_host.py

@@ -85,6 +85,6 @@ class ActionModule(ActionBase):
             if k not in special_args:
                 host_vars[k] = self._task.args[k]
 
-        result['changed'] = True
+        result['changed'] = False
         result['add_host'] = dict(host_name=name, groups=new_groups, host_vars=host_vars)
         return result

lib/ansible/plugins/strategy/__init__.py

@@ -641,7 +641,7 @@ class StrategyBase:
                     if 'add_host' in result_item:
                         # this task added a new host (add_host module)
                         new_host_info = result_item.get('add_host', dict())
-                        self._add_host(new_host_info, iterator)
+                        self._add_host(new_host_info, result_item)
 
                     elif 'add_group' in result_item:
                         # this task added a new group (group_by module)
@@ -792,11 +792,13 @@ class StrategyBase:
 
         return ret_results
 
-    def _add_host(self, host_info, iterator):
+    def _add_host(self, host_info, result_item):
         '''
         Helper function to add a new host to inventory based on a task result.
         '''
 
+        changed = False
+
         if host_info:
             host_name = host_info.get('host_name')
 
@@ -804,20 +806,30 @@ class StrategyBase:
             if host_name not in self._inventory.hosts:
                 self._inventory.add_host(host_name, 'all')
                 self._hosts_cache_all.append(host_name)
+                changed = True
             new_host = self._inventory.hosts.get(host_name)
 
             # Set/update the vars for this host
-            new_host.vars = combine_vars(new_host.get_vars(), host_info.get('host_vars', dict()))
+            new_host_vars = new_host.get_vars()
+            new_host_combined_vars = combine_vars(new_host_vars, host_info.get('host_vars', dict()))
+            if new_host_vars != new_host_combined_vars:
+                new_host.vars = new_host_combined_vars
+                changed = True
 
             new_groups = host_info.get('groups', [])
             for group_name in new_groups:
                 if group_name not in self._inventory.groups:
                     group_name = self._inventory.add_group(group_name)
+                    changed = True
                 new_group = self._inventory.groups[group_name]
-                new_group.add_host(self._inventory.hosts[host_name])
+                if new_group.add_host(self._inventory.hosts[host_name]):
+                    changed = True
 
             # reconcile inventory, ensures inventory rules are followed
-            self._inventory.reconcile_inventory()
+            if changed:
+                self._inventory.reconcile_inventory()
+
+            result_item['changed'] = changed
 
     def _add_group(self, host, result_item):
         '''

test/integration/targets/add_host/tasks/main.yml

@@ -37,3 +37,81 @@
     - groups['bogusgroup'] is not defined # same check as above to ensure that bogus groups are undefined...
     - groups['newdynamicgroup'] is defined
     - "'newdynamichost' in groups['newdynamicgroup']"
+
+# Tests for idempotency
+- name: Add testhost01 dynamic host
+  add_host:
+    name: testhost01
+  register: add_testhost01
+
+- name: Try adding testhost01 again, with no changes
+  add_host:
+    name: testhost01
+  register: add_testhost01_idem
+
+- name: Add a host variable to testhost01
+  add_host:
+    name: testhost01
+    foo: bar
+  register: hostvar_testhost01
+
+- name: Add the same host variable to testhost01, with no changes
+  add_host:
+    name: testhost01
+    foo: bar
+  register: hostvar_testhost01_idem
+
+- name: Add another host, testhost02
+  add_host:
+    name: testhost02
+  register: add_testhost02
+
+- name: Add it again for good measure
+  add_host:
+    name: testhost02
+  register: add_testhost02_idem
+
+- name: Add testhost02 to a group
+  add_host:
+    name: testhost02
+    groups:
+      - testhostgroup
+  register: add_group_testhost02
+
+- name: Add testhost01 to the same group
+  add_host:
+    name: testhost01
+    groups:
+      - testhostgroup
+  register: add_group_testhost01
+
+- name: Add testhost02 to the group again
+  add_host:
+    name: testhost02
+    groups:
+      - testhostgroup
+  register: add_group_testhost02_idem
+
+- name: Add testhost01 to the group again
+  add_host:
+    name: testhost01
+    groups:
+      - testhostgroup
+  register: add_group_testhost01_idem
+
+- assert:
+    that:
+      - add_testhost01 is changed
+      - add_testhost01_idem is not changed
+      - hostvar_testhost01 is changed
+      - hostvar_testhost01_idem is not changed
+      - add_testhost02 is changed
+      - add_testhost02_idem is not changed
+      - add_group_testhost02 is changed
+      - add_group_testhost01 is changed
+      - add_group_testhost02_idem is not changed
+      - add_group_testhost01_idem is not changed
+      - groups['testhostgroup']|length == 2
+      - "'testhost01' in groups['testhostgroup']"
+      - "'testhost02' in groups['testhostgroup']"
+      - hostvars['testhost01']['foo'] == 'bar'