add check_mode option for tasks (#16056)

* add check_mode option for tasks

includes example testcases for the template module

* extend check_mode option

* replace always_run, see also proposal rename_always_run
* rename always_run where used and add deprecation warning
* add some documentation

* have check_mode overwrite always_run

* use unique template name to prevent conflicts

test_check_mode was right before, but failed due to using the same filename as other roles

* still mention always_run in the docs

* set deprecation of always_run to version 2.4

* fix rst style

* expand documentation on per-task check mode

docsite/rst/playbooks_checkmode.rst

@@ -20,31 +20,50 @@ Example::
 
 .. _forcing_to_run_in_check_mode:
 
-Running a task in check mode
+Enabling or disabling check mode for tasks
-````````````````````````````
+``````````````````````````````````````````
 
-.. versionadded:: 1.3
+.. versionadded:: 2.2
 
-Sometimes you may want to have a task to be executed even in check
+Sometimes you may want to modify the check mode behavior of individual tasks. This is done via the ``check_mode`` option, which can
-mode. To achieve this, use the `always_run` clause on the task. Its
+be added to tasks. 
-value is a Jinja2 expression, just like the `when` clause. In simple
+
-cases a boolean YAML value would be sufficient as a value.
+There are two options:
+
+1. Force a task to **run in check mode**, even when the playbook is called **without** ``--check``. This is called ``check_mode: yes``.
+2. Force a task to **run in normal mode** and make changes to the system, even when the playbook is called **with** ``--check``. This is called ``check_mode: no``.
+
+.. note:: Prior to version 2.2 only the the equivalent of ``check_mode: no`` existed. The notation for that was ``always_run: yes``.
+
+Instead of ``yes``/``no`` you can use a Jinja2 expression, just like the ``when`` clause.
 
 Example::
 
     tasks:
 
-      - name: this task is run even in check mode
+      - name: this task will make changes to the system even in check mode
         command: /something/to/run --even-in-check-mode
-        always_run: yes
+        check_mode: no
 
-As a reminder, a task with a `when` clause evaluated to false, will
+      - name: this task will always run under checkmode and not change the system
-still be skipped even if it has a `always_run` clause evaluated to
+        lineinfile: line="important config" dest=/path/to/myconfig.conf state=present
-true. 
+        check_mode: yes
 
-Also if you want to skip, or ignore errors on some tasks in check mode
+
-you can use a boolean magic variable `ansible_check_mode` (added in version 2.1)
+Running single tasks with ``check_mode: yes`` can be useful to write tests for
-which will be set to `True` during check mode.
+ansible modules, either to test the module itself or to the the conditions under
+which a module would make changes. 
+With ``register`` (see :doc:`playbooks_conditionals`) you can check the
+potential changes.
+
+Information about check mode in variables
+`````````````````````````````````````````
+
+.. versionadded:: 2.1
+
+If you want to skip, or ignore errors on some tasks in check mode
+you can use a boolean magic variable ``ansible_check_mode``
+which will be set to ``True`` during check mode.
 
 Example::
 

docsite/rst/test_strategies.rst

@@ -42,7 +42,7 @@ existing system, using the `--check` flag to the `ansible` command will report i
 bring the system into a desired state.
 
 This can let you know up front if there is any need to deploy onto the given system.  Ordinarily scripts and commands don't run in check mode, so if you
-want certain steps to always execute in check mode, such as calls to the script module, add the 'always_run' flag::
+want certain steps to always execute in check mode, such as calls to the script module, disable check mode for those tasks::
 
 
    roles:
@@ -50,7 +50,7 @@ want certain steps to always execute in check mode, such as calls to the script
 
    tasks:
      - script: verify.sh
-       always_run: True
+       check_mode: no
 
 Modules That Are Useful for Testing
 ```````````````````````````````````

lib/ansible/playbook/base.py

@@ -63,6 +63,7 @@ class Base:
     _always_run           = FieldAttribute(isa='bool')
     _run_once             = FieldAttribute(isa='bool')
     _ignore_errors        = FieldAttribute(isa='bool')
+    _check_mode = FieldAttribute(isa='bool')
 
     # param names which have been deprecated/removed
     DEPRECATED_ATTRIBUTES = [

lib/ansible/playbook/play_context.py

@@ -440,10 +440,15 @@ class PlayContext(Base):
         # set become defaults if not previouslly set
         task.set_become_defaults(new_info.become, new_info.become_method, new_info.become_user)
 
-        # have always_run override check mode
         if task.always_run:
+            display.deprecated("always_run is deprecated. Use check_mode = no instead.", version="2.4", removed=False)
             new_info.check_mode = False
 
+        # check_mode replaces always_run, overwrite always_run if both are given
+        if task.check_mode is not None:
+            new_info.check_mode = task.check_mode
+
+
         return new_info
 
     def make_become_cmd(self, cmd, executable=None):

test/integration/roles/test_always_run/tasks/main.yml

@@ -18,7 +18,7 @@
 
 - name: run a command while in check mode
   shell: echo "running"
-  always_run: yes
+  check_mode: no
   register: result
 
 - name: assert that the command was run

test/integration/roles/test_check_mode/tasks/main.yml

@@ -17,23 +17,30 @@
 # along with Ansible.  If not, see <http://www.gnu.org/licenses/>.
 
 - name: fill in a basic template in check mode
-  template: src=foo.j2 dest={{output_dir}}/foo.templated mode=0644
+  template: src=foo.j2 dest={{output_dir}}/checkmode_foo.templated mode=0644
   register: template_result
 
+- name: check whether file exists
+  stat: path={{output_dir}}/checkmode_foo.templated
+  register: foo
+
 - name: verify that the file was marked as changed in check mode
   assert: 
     that: 
-      - "template_result.changed == true"
+      - "template_result|changed"
+      - "not foo.stat.exists"
 
-- name: Actually create the file
+- name: Actually create the file, disable check mode
-  template: src=foo.j2 dest={{output_dir}}/foo.templated2 mode=0644
+  template: src=foo.j2 dest={{output_dir}}/checkmode_foo.templated2 mode=0644
-  always_run: True
+  check_mode: no
+  register: checkmode_disabled
 
-- name: fill in a basic template in check mode
+- name: fill in template with new content
-  template: src=foo.j2 dest={{output_dir}}/foo.templated2 mode=0644
+  template: src=foo.j2 dest={{output_dir}}/checkmode_foo.templated2 mode=0644
   register: template_result2
 
-- name: verify that the file was marked as not changed in check mode
+- name: verify that the file was not changed
   assert: 
     that: 
-      - "template_result2.changed == false"
+      - "checkmode_disabled|changed"
+      - "not template_result2|changed"

test/integration/roles/test_template/tasks/main.yml

@@ -179,3 +179,49 @@
     that:
       - "template_result.changed == False"
 
+
+# check_mode
+
+- name: fill in a basic template in check mode
+  template: src=short.j2 dest={{output_dir}}/short.templated
+  register: template_result
+  check_mode: True
+
+- name: check file exists
+  stat: path={{output_dir}}/short.templated
+  register: templated
+
+- name: verify that the file was marked as changed in check mode but was not created
+  assert: 
+    that: 
+      - "not templated.stat.exists"
+      - "template_result|changed"
+
+- name: fill in a basic template
+  template: src=short.j2 dest={{output_dir}}/short.templated
+
+- name: fill in a basic template in check mode
+  template: src=short.j2 dest={{output_dir}}/short.templated
+  register: template_result
+  check_mode: True
+
+- name: verify that the file was marked as not changes in check mode
+  assert: 
+    that: 
+      - "not template_result|changed"
+      - "'templated_var_loaded' in lookup('file', '{{output_dir | expanduser}}/short.templated')"
+
+- name: change var for the template
+  set_fact: 
+    templated_var: "changed"
+
+- name: fill in a basic template with changed var in check mode
+  template: src=short.j2 dest={{output_dir}}/short.templated
+  register: template_result
+  check_mode: True
+
+- name: verify that the file was marked as changed in check mode but the content was not changed
+  assert: 
+    that: 
+      - "'templated_var_loaded' in lookup('file', '{{output_dir | expanduser }}/short.templated')"
+      - "template_result|changed"

test/integration/roles/test_template/templates/short.j2

@@ -0,0 +1 @@
+{{ templated_var }}