clarify backup_file (#1391) (#1440)

* add conditional

Also backup_file would not be present if updated is not changed

* clarify docs too

* better desc

(cherry picked from commit ba39855)

Co-authored-by: Brian Coca <bcoca@users.noreply.github.com>

docs/docsite/rst/reference_appendices/common_return_values.rst

@@ -18,7 +18,7 @@ Common
 
 backup_file
 ```````````
-For those modules that implement `backup=no|yes` when manipulating files, a path to the backup file created.
+For those modules that implement `backup=no|yes` when manipulating files, a path to the backup file created if original file was changed.
 
     .. code-block:: console
 

docs/docsite/rst/reference_appendices/faq.rst

@@ -826,29 +826,32 @@ and backups, which most file based modules also support:
 
 .. code-block:: yaml
 
-    - name: update config and backout if validation fails
+    - name: maintain config and backout if validation after change fails
       block:
-         - name: do the actual update, works with copy, lineinfile and any action that allows for `backup`.
-           template: src=template.j2 dest=/x/y/z backup=yes moreoptions=stuff
-           register: updated
+        - name: do the actual update, works with copy, lineinfile and any action that allows for `backup`.
+          template: src=template.j2 dest=/x/y/z backup=yes moreoptions=stuff
+          register: updated
 
         - name: run validation, this will change a lot as needed. We assume it returns an error when not passing, use `failed_when` if otherwise.
           shell: run_validation_commmand
           become: true
           become_user: requiredbyapp
           environment:
             WEIRD_REQUIREMENT: 1
+          when: updated is changed
      rescue:
         - name: restore backup file to original, in the hope the previous configuration was working.
           copy:
              remote_src: true
              dest: /x/y/z
              src: "{{ updated['backup_file'] }}"
+          when: updated is changed
      always:
         - name: We choose to always delete backup, but could copy or move, or only delete in rescue.
           file:
              path: "{{ updated['backup_file'] }}"
              state: absent
+          when: updated is changed
 
 .. _jinja2_faqs: