Let command always return stdout & stderr (#73004)

The `command` module does not return stdout & sterr when calling
a non existing executable or an unknown exception arises. This fix
lets the module return empty byte strings in those cases.

changelogs/fragments/73004-let-command-always-return-stdout-and-stderr.yml

@@ -0,0 +1,2 @@
+bugfixes:
+- Command module now returns stdout & stderr if executable is missing or an unknown error occurs

lib/ansible/module_utils/basic.py

@@ -2772,10 +2772,10 @@ class AnsibleModule(object):
             rc = cmd.returncode
         except (OSError, IOError) as e:
             self.log("Error Executing CMD:%s Exception:%s" % (self._clean_args(args), to_native(e)))
-            self.fail_json(rc=e.errno, msg=to_native(e), cmd=self._clean_args(args))
+            self.fail_json(rc=e.errno, stdout=b'', stderr=b'', msg=to_native(e), cmd=self._clean_args(args))
         except Exception as e:
             self.log("Error Executing CMD:%s Exception:%s" % (self._clean_args(args), to_native(traceback.format_exc())))
-            self.fail_json(rc=257, msg=to_native(e), exception=traceback.format_exc(), cmd=self._clean_args(args))
+            self.fail_json(rc=257, stdout=b'', stderr=b'', msg=to_native(e), exception=traceback.format_exc(), cmd=self._clean_args(args))
 
         # Restore env settings
         for key, val in old_env_vals.items():

test/integration/targets/command_nonexisting/aliases

@@ -0,0 +1 @@
+shippable/posix/group2

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

@@ -0,0 +1,4 @@
+- command: commandthatdoesnotexist --would-be-awkward
+  register: res
+  changed_when: "'changed' in res.stdout"
+  failed_when: "res.stdout != '' or res.stderr != ''"

test/units/module_utils/basic/test_command_nonexisting.py

@@ -0,0 +1,31 @@
+from __future__ import (absolute_import, division, print_function)
+__metaclass__ = type
+
+import sys
+import pytest
+import json
+import sys
+import pytest
+import subprocess
+import ansible.module_utils.basic
+from ansible.module_utils._text import to_bytes
+from ansible.module_utils import basic
+
+
+def test_run_non_existent_command(monkeypatch):
+    """ Test that `command` returns std{out,err} even if the executable is not found """
+    def fail_json(msg, **kwargs):
+        assert kwargs["stderr"] == b''
+        assert kwargs["stdout"] == b''
+        sys.exit(1)
+
+    def popen(*args, **kwargs):
+        raise OSError()
+
+    monkeypatch.setattr(basic, '_ANSIBLE_ARGS', to_bytes(json.dumps({'ANSIBLE_MODULE_ARGS': {}})))
+    monkeypatch.setattr(subprocess, 'Popen', popen)
+
+    am = basic.AnsibleModule(argument_spec={})
+    monkeypatch.setattr(am, 'fail_json', fail_json)
+    with pytest.raises(SystemExit):
+        am.run_command("lecho", "whatever")