docker_container idempotency: work around Docker not returning true configured command when command is [] (#1085)

* Work around Docker not returning true configured command when command is [].

* Lint.

* Add test.

* Add changelog fragment.

changelogs/fragments/1085-docker_container-command-empty.yml

@@ -0,0 +1,2 @@
+bugfixes:
+  - "docker_container - fix idempotency if ``command=[]`` and ``command_handling=correct`` (https://github.com/ansible-collections/community.docker/issues/1080, https://github.com/ansible-collections/community.docker/pull/1085)."

plugins/module_utils/module_container/docker_api.py

@@ -1274,6 +1274,34 @@ def _preprocess_container_names(module, client, api_version, value):
     return 'container:{0}'.format(container['Id'])
 
 
+def _get_value_command(module, container, api_version, options, image, host_info):
+    value = container['Config'].get('Cmd', _SENTRY)
+    if value is _SENTRY:
+        return {}
+    return {"command": value}
+
+
+def _set_value_command(module, data, api_version, options, values):
+    if "command" not in values:
+        return
+    value = values["command"]
+    data['Cmd'] = value
+
+
+def _get_expected_values_command(module, client, api_version, options, image, values, host_info):
+    expected_values = {}
+    if 'command' in values:
+        command = values['command']
+        if command == [] and image and image["Config"].get("Cmd"):
+            command = image["Config"].get("Cmd")
+        expected_values['command'] = command
+    return expected_values
+
+
+def _needs_container_image_command(values):
+    return values.get('command') == []
+
+
 OPTION_AUTO_REMOVE.add_engine('docker_api', DockerAPIEngine.host_config_value('AutoRemove'))
 
 OPTION_BLKIO_WEIGHT.add_engine('docker_api', DockerAPIEngine.host_config_value('BlkioWeight', update_parameter='BlkioWeight'))
@@ -1286,7 +1314,12 @@ OPTION_CGROUP_NS_MODE.add_engine('docker_api', DockerAPIEngine.host_config_value
 
 OPTION_CGROUP_PARENT.add_engine('docker_api', DockerAPIEngine.host_config_value('CgroupParent'))
 
-OPTION_COMMAND.add_engine('docker_api', DockerAPIEngine.config_value('Cmd'))
+OPTION_COMMAND.add_engine('docker_api', DockerAPIEngine(
+    get_value=_get_value_command,
+    set_value=_set_value_command,
+    get_expected_values=_get_expected_values_command,
+    needs_container_image=_needs_container_image_command,
+))
 
 OPTION_CPU_PERIOD.add_engine('docker_api', DockerAPIEngine.host_config_value('CpuPeriod', update_parameter='CpuPeriod'))
 

tests/integration/targets/docker_container/tasks/tests/options.yml

@@ -385,6 +385,16 @@
     force_kill: true
   register: command_5
 
+- name: command (correct, empty list, idempotency)
+  docker_container:
+    image: "{{ docker_test_image_alpine }}"
+    command_handling: correct
+    command: []
+    name: "{{ cname }}"
+    state: present  # the container will use the default command and likely has been exited by this point, so don't use 'state: started' here
+    force_kill: true
+  register: command_6
+
 - name: cleanup
   docker_container:
     name: "{{ cname }}"
@@ -399,6 +409,7 @@
       - command_3 is not changed
       - command_4 is changed
       - command_5 is changed
+      - command_6 is not changed
 
 ####################################################################
 ## cpu_period ######################################################