Fixes #17958: use stderr instead of the default stdout for fatal errors (#17962)

* add a callback plugin that sends failures to stderr

* fix warnings

lib/ansible/plugins/callback/stderr.py

@@ -0,0 +1,80 @@
+# (c) 2017, Frederic Van Espen <github@freh.be>
+#
+# This file is part of Ansible
+#
+# Ansible is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# Ansible is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with Ansible.  If not, see <http://www.gnu.org/licenses/>.
+
+# Make coding more python3-ish
+from __future__ import (absolute_import, division, print_function)
+__metaclass__ = type
+
+from ansible import constants as C
+from ansible.plugins.callback.default import CallbackModule as CallbackModule_default
+
+
+class CallbackModule(CallbackModule_default):
+
+    '''
+    This is the stderr callback plugin, which reuses the default
+    callback plugin but sends error output to stderr.
+    '''
+
+    CALLBACK_VERSION = 2.0
+    CALLBACK_TYPE = 'stdout'
+    CALLBACK_NAME = 'stderr'
+
+    def __init__(self):
+
+        self.super_ref = super(CallbackModule, self)
+        self.super_ref.__init__()
+
+    def v2_runner_on_failed(self, result, ignore_errors=False):
+
+        delegated_vars = result._result.get('_ansible_delegated_vars', None)
+        self._clean_results(result._result, result._task.action)
+
+        if self._play.strategy == 'free' and self._last_task_banner != result._task._uuid:
+            self._print_task_banner(result._task)
+
+        self._handle_exception(result._result, errors_to_stderr=True)
+        self._handle_warnings(result._result)
+
+        if result._task.loop and 'results' in result._result:
+            self._process_items(result)
+
+        else:
+            if delegated_vars:
+                self._display.display("fatal: [%s -> %s]: FAILED! => %s" % (result._host.get_name(), delegated_vars['ansible_host'],
+                                                                            self._dump_results(result._result)), color=C.COLOR_ERROR,
+                                      stderr=True)
+            else:
+                self._display.display("fatal: [%s]: FAILED! => %s" % (result._host.get_name(), self._dump_results(result._result)),
+                                      color=C.COLOR_ERROR, stderr=True)
+
+        if ignore_errors:
+            self._display.display("...ignoring", color=C.COLOR_SKIP)
+
+    def _handle_exception(self, result, errors_to_stderr=False):
+
+        if 'exception' in result:
+            msg = "An exception occurred during task execution. "
+            if self._display.verbosity < 3:
+                # extract just the actual error message from the exception text
+                error = result['exception'].strip().split('\n')[-1]
+                msg += "To see the full traceback, use -vvv. The error was: %s" % error
+            else:
+                msg = "The full traceback is:\n" + result['exception']
+                del result['exception']
+
+            self._display.display(msg, color=C.COLOR_ERROR, stderr=errors_to_stderr)