Add debug strategy plugin (#15125)

* Add debug strategy plugin

* Fix Python 2-3 compatiblity issue

* Add document for debug strategy

5 files changed, 330 insertions, 1 deletions

diff --git a/ansible-core-sitemap.xml b/ansible-core-sitemap.xml
index 84a048d311..ea05e356f3 100644
--- a/ansible-core-sitemap.xml
+++ b/ansible-core-sitemap.xml
@@ -113,6 +113,11 @@
 		<priority>0.5</priority>
 	</url>
 	<url>
+		<loc>http://docs.ansible.com/ansible/playbooks_debugger.html</loc>
+		<changefreq>weekly</changefreq>
+		<priority>0.5</priority>
+	</url>
+	<url>
 		<loc>http://docs.ansible.com/ansible/become.html</loc>
 		<changefreq>weekly</changefreq>
 		<priority>0.5</priority>
@@ -2713,4 +2718,4 @@
 		<priority>0.3</priority>
 	</url>
 
-</urlset>
\ No newline at end of file
+</urlset>
diff --git a/docsite/rst/playbooks_debugger.rst b/docsite/rst/playbooks_debugger.rst
new file mode 100644
index 0000000000..dc22d7b9a4
--- /dev/null
+++ b/docsite/rst/playbooks_debugger.rst
@@ -0,0 +1,159 @@
+Playbook Debugger
+=================
+
+.. contents:: Topics
+
+In 2.1 we added a ``debug`` strategy. This strategy enables you to invoke a debugger when a task is
+failed, and check several info, such as the value of a variable. Also, it is possible to update module
+arguments in the debugger, and run the failed task again with new arguments to consider how you
+can fix an issue.
+
+To use ``debug`` strategy, change ``strategy`` attribute like this::
+
+    - hosts: test
+      strategy: debug
+      tasks:
+      ...
+
+For example, run the playbook below::
+
+    - hosts: test
+      strategy: debug
+      gather_facts: no
+      vars:
+        var1: value1
+      tasks:
+        - name: wrong variable
+          ping: data={{ wrong_var }}
+
+The debugger is invoked since *wrong_var* variable is undefined. Let's change the module's args,
+and run the task again::
+
+    PLAY ***************************************************************************
+
+    TASK [wrong variable] **********************************************************
+    fatal: [192.168.1.1]: FAILED! => {"failed": true, "msg": "ERROR! 'wrong_var' is undefined"}
+    Debugger invoked
+    (debug) p result
+    {'msg': u"ERROR! 'wrong_var' is undefined", 'failed': True}
+    (debug) p task.args
+    {u'data': u'{{ wrong_var }}'}
+    (debug) task.args['data'] = '{{ var1 }}'
+    (debug) p task.args
+    {u'data': '{{ var1 }}'}
+    (debug) redo
+    ok: [192.168.1.1]
+
+    PLAY RECAP *********************************************************************
+    192.168.1.1               : ok=1    changed=0    unreachable=0    failed=0
+
+This time, the task runs successfully!
+
+.. _available_commands:
+
+Available Commands
+++++++++++++++++++
+
+.. _p_command:
+
+p *task/vars/host/result*
+`````````````````````````
+
+Print values used to execute a module::
+
+    (debug) p task
+    TASK: install package
+    (debug) p task.args
+    {u'name': u'{{ pkg_name }}'}
+    (debug) p vars
+    {u'ansible_all_ipv4_addresses': [u'192.168.1.1'],
+     u'ansible_architecture': u'x86_64',
+     ...
+    }
+    (debug) p vars['pkg_name']
+    u'bash'
+    (debug) p host
+    192.168.1.1
+    (debug) p result
+    {'_ansible_no_log': False,
+     'changed': False,
+     u'failed': True,
+     ...
+     u'msg': u"No package matching 'not_exist' is available"}
+
+.. _update_args_command:
+
+task.args[*key*] = *value*
+``````````````````````````
+
+Update module's argument.
+
+If you run a playbook like this::
+
+    - hosts: test
+      strategy: debug
+      gather_facts: yes
+      vars:
+        pkg_name: not_exist
+      tasks:
+        - name: install package
+          apt: name={{ pkg_name }}
+
+Debugger is invoked due to wrong package name, so let's fix the module's args::
+
+    (debug) p task.args
+    {u'name': u'{{ pkg_name }}'}
+    (debug) task.args['name'] = 'bash'
+    (debug) p task.args
+    {u'name': 'bash'}
+    (debug) redo
+
+Then the task runs again with new args.
+
+.. _update_vars_command:
+
+vars[*key*] = *value*
+`````````````````````
+
+Update vars.
+
+Let's use the same playbook above, but fix vars instead of args::
+
+    (debug) p vars['pkg_name']
+    u'not_exist'
+    (debug) vars['pkg_name'] = 'bash'
+    (debug) p vars['pkg_name']
+    'bash'
+    (debug) redo
+
+Then the task runs again with new vars.
+
+.. _redo_command:
+
+r(edo)
+``````
+
+Run the task again.
+
+.. _continue_command:
+
+c(ontinue)
+``````````
+
+Just continue.
+
+.. _quit_command:
+
+q(uit)
+``````
+
+Quit from the debugger. The playbook execution is aborted.
+
+.. seealso::
+
+   :doc:`playbooks`
+       An introduction to playbooks
+   `User Mailing List <http://groups.google.com/group/ansible-devel>`_
+       Have a question?  Stop by the google group!
+   `irc.freenode.net <http://irc.freenode.net>`_
+       #ansible IRC chat channel
diff --git a/docsite/rst/playbooks_special_topics.rst b/docsite/rst/playbooks_special_topics.rst
index 6593d20a54..3e31d38e22 100644
--- a/docsite/rst/playbooks_special_topics.rst
+++ b/docsite/rst/playbooks_special_topics.rst
@@ -11,6 +11,7 @@ and adopt these only if they seem relevant or useful to your environment.
    playbooks_acceleration
    playbooks_async
    playbooks_checkmode
+   playbooks_debugger
    playbooks_delegation
    playbooks_environment
    playbooks_error_handling
diff --git a/docsite/rst/playbooks_strategies.rst b/docsite/rst/playbooks_strategies.rst
index a9095bc083..a34daa1c1f 100644
--- a/docsite/rst/playbooks_strategies.rst
+++ b/docsite/rst/playbooks_strategies.rst
@@ -26,6 +26,8 @@ The strategies are implemented via a new type of plugin, this means that in the
 execution types can be added, either locally by users or to Ansible itself by
 a code contribution.
 
+One example is ``debug`` strategy. See :doc:`playbooks_debugger` for details.
+
 .. seealso::
 
    :doc:`playbooks`
diff --git a/lib/ansible/plugins/strategy/debug.py b/lib/ansible/plugins/strategy/debug.py
new file mode 100644
index 0000000000..fbfe01cbe1
--- /dev/null
+++ b/lib/ansible/plugins/strategy/debug.py
@@ -0,0 +1,162 @@
+
+from __future__ import (absolute_import, division, print_function)
+__metaclass__ = type
+
+import cmd
+import pprint
+import sys
+
+from ansible.plugins.strategy import linear
+from ansible.plugins.strategy import StrategyBase
+
+try:
+    from __main__ import display
+except ImportError:
+    from ansible.utils.display import Display
+    display = Display()
+
+
+class NextAction(object):
+    """ The next action after an interpreter's exit. """
+    REDO = 1
+    CONTINUE = 2
+    EXIT = 3
+
+    def __init__(self, result=EXIT):
+        self.result = result
+
+
+class StrategyModule(linear.StrategyModule, StrategyBase):
+    # Usually inheriting linear.StrategyModule is enough. However, StrategyBase class must be
+    # direct ancestor to be considered as strategy plugin, and so we inherit the class here.
+
+    def __init__(self, tqm):
+        self.curr_tqm = tqm
+        StrategyBase.__init__(self, tqm)
+
+    def _queue_task(self, host, task, task_vars, play_context):
+        self.curr_host = host
+        self.curr_task = task
+        self.curr_task_vars = task_vars
+        self.curr_play_context = play_context
+
+        StrategyBase._queue_task(self, host, task, task_vars, play_context)
+
+    def _process_pending_results(self, iterator, one_pass=False):
+        if not hasattr(self, "curr_host"):
+            return StrategyBase._process_pending_results(self, iterator, one_pass)
+
+        prev_host_state = iterator.get_host_state(self.curr_host)
+        results = StrategyBase._process_pending_results(self, iterator, one_pass)
+
+        while self._need_debug(results):
+            next_action = NextAction()
+            dbg = Debugger(self, results, next_action)
+            dbg.cmdloop()
+
+            if next_action.result == NextAction.REDO:
+                # rollback host state
+                self.curr_tqm.clear_failed_hosts()
+                iterator._host_states[self.curr_host.name] = prev_host_state
+                if reduce(lambda total, res : res.is_failed() or total, results, False):
+                    self._tqm._stats.failures[self.curr_host.name] -= 1
+                elif reduce(lambda total, res : res.is_unreachable() or total, results, False):
+                    self._tqm._stats.dark[self.curr_host.name] -= 1
+
+                # redo
+                StrategyBase._queue_task(self, self.curr_host, self.curr_task, self.curr_task_vars, self.curr_play_context)
+                results = StrategyBase._process_pending_results(self, iterator, one_pass)
+            elif next_action.result == NextAction.CONTINUE:
+                break
+            elif next_action.result == NextAction.EXIT:
+                exit(1)
+
+        return results
+
+    def _need_debug(self, results):
+        return reduce(lambda total, res : res.is_failed() or res.is_unreachable() or total, results, False)
+
+
+class Debugger(cmd.Cmd):
+    prompt = '(debug) '  # debugger
+    prompt_continuous = '> '  # multiple lines
+
+    def __init__(self, strategy_module, results, next_action):
+        # cmd.Cmd is old-style class
+        cmd.Cmd.__init__(self)
+
+        self.intro = "Debugger invoked"
+        self.scope = {}
+        self.scope['task'] = strategy_module.curr_task
+        self.scope['vars'] = strategy_module.curr_task_vars
+        self.scope['host'] = strategy_module.curr_host
+        self.scope['result'] = results[0]._result
+        self.scope['results'] = results  # for debug of this debugger
+        self.next_action = next_action
+
+    def cmdloop(self):
+        try:
+            cmd.Cmd.cmdloop(self)
+        except KeyboardInterrupt:
+            pass
+
+    def do_EOF(self, args):
+        return self.do_quit(args)
+
+    def do_quit(self, args):
+        display.display('aborted')
+        self.next_action.result = NextAction.EXIT
+        return True
+
+    do_q = do_quit
+
+    def do_continue(self, args):
+        self.next_action.result = NextAction.CONTINUE
+        return True
+
+    do_c = do_continue
+
+    def do_redo(self, args):
+        self.next_action.result = NextAction.REDO
+        return True
+
+    do_r = do_redo
+
+    def evaluate(self, args):
+        try:
+            return eval(args, globals(), self.scope)
+        except:
+            t, v = sys.exc_info()[:2]
+            if isinstance(t, str):
+                exc_type_name = t
+            else:
+                exc_type_name = t.__name__
+            display.display('***%s:%s' % (exc_type_name, repr(v)))
+            raise
+
+    def do_p(self, args):
+        try:
+            result = self.evaluate(args)
+            display.display(pprint.pformat(result))
+        except:
+            pass
+
+    def execute(self, args):
+        try:
+            code = compile(args + '\n', '<stdin>', 'single')
+            exec(code, globals(), self.scope)
+        except:
+            t, v = sys.exc_info()[:2]
+            if type(t) == type(''):
+                exc_type_name = t
+            else:
+                exc_type_name = t.__name__
+            display.display('***%s:%s' % (exc_type_name, repr(v)))
+            raise
+
+    def default(self, line):
+        try:
+            self.execute(line)
+            display.display(pprint.pformat(result))
+        except:
+            pass