bug(lookup/merge_variables): Fix rendering foreign variables (#8303)

* manually prepare variables of foreign host including hostvars property

* render variables from context of current host

* add integration test for cross host merge

* lint fixes

* adjust cross host merge unit tests to provide a tiny bit of the HostVars Class API

* add license information

* lint

* add changelog fragment

* Update tests/integration/targets/lookup_merge_variables/test_cross_host_merge_play.yml

Okay

Co-authored-by: Mark <40321020+m-a-r-k-e@users.noreply.github.com>

* Update tests/integration/targets/lookup_merge_variables/test_cross_host_merge_play.yml

Okay

Co-authored-by: Mark <40321020+m-a-r-k-e@users.noreply.github.com>

* Update tests/integration/targets/lookup_merge_variables/test_cross_host_merge_play.yml

Okay

Co-authored-by: Mark <40321020+m-a-r-k-e@users.noreply.github.com>

* rename _HostVars to HostVarsMock

* removing unnecessary task

---------

Co-authored-by: Gitlab CI <alexander.petrenz@posteo.de>
Co-authored-by: Mark <40321020+m-a-r-k-e@users.noreply.github.com>

tests/integration/targets/lookup_merge_variables/runme.sh

@@ -14,3 +14,6 @@ ANSIBLE_MERGE_VARIABLES_PATTERN_TYPE=suffix \
 
 ANSIBLE_LOG_PATH=/tmp/ansible-test-merge-variables \
     ansible-playbook -i test_inventory_all_hosts.yml test_all_hosts.yml "$@"
+
+ANSIBLE_LOG_PATH=/tmp/ansible-test-merge-variables \
+    ansible-playbook -i test_cross_host_merge_inventory.yml test_cross_host_merge_play.yml "$@"

tests/integration/targets/lookup_merge_variables/test_cross_host_merge_inventory.yml

@@ -0,0 +1,33 @@
+---
+# Copyright (c) 2020, Thales Netherlands
+# Copyright (c) 2021, Ansible Project
+# GNU General Public License v3.0+ (see LICENSES/GPL-3.0-or-later.txt or https://www.gnu.org/licenses/gpl-3.0.txt)
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+common:
+  vars:
+    provider_instances:
+      servicedata1:
+        host: "{{ hostvars[groups['provider'] | first].inventory_hostname }}"
+        user: usr
+        pass: pwd
+      servicedata2:
+        host: down
+        user: usr2
+        pass: pwd2
+  hosts:
+    host1:
+    host2:
+
+consumer:
+  vars:
+    service_data: "{{ provider_instances.servicedata1 }}"
+    merge2__1: "{{ service_data }}"  # service_data is a variable only known to host2, so normally it´s not available for host1 that is performing the merge
+  hosts:
+    host2:
+
+provider:
+  vars:
+    merge_result: "{{ lookup('community.general.merge_variables', 'merge2__', pattern_type='prefix', groups=['consumer']) }}"
+  hosts:
+    host1:

tests/integration/targets/lookup_merge_variables/test_cross_host_merge_play.yml

@@ -0,0 +1,21 @@
+---
+# Copyright (c) 2020, Thales Netherlands
+# Copyright (c) 2021, Ansible Project
+# GNU General Public License v3.0+ (see LICENSES/GPL-3.0-or-later.txt or https://www.gnu.org/licenses/gpl-3.0.txt)
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+- name: Test merge_variables lookup plugin (merging host reference variables)
+  hosts: host1
+  connection: local
+  gather_facts: false
+  tasks:
+    - name: Print merge result
+      ansible.builtin.debug:
+        msg: "{{ merge_result }}"
+    - name: Validate merge result
+      ansible.builtin.assert:
+        that:
+          - "merge_result | length == 3"
+          - "merge_result.host == 'host1'"
+          - "merge_result.user == 'usr'"
+          - "merge_result.pass == 'pwd'"