more useful messages when module failure (ansible#43576)

* more useful messages when module failure

specially if the 'interpreter' is not found

* 1 less var

* shebang can be none

* remove typoes

changelogs/fragments/missing_interpreter.yml

@@ -0,0 +1,2 @@
+bugfixes:
+    - nicer message when we are missing interpreter

lib/ansible/plugins/action/__init__.py

@@ -60,6 +60,8 @@ def __init__(self, task, connection, play_context, loader, templar, shared_loade
         # Backwards compat: self._display isn't really needed, just import the global display and use that.
         self._display = display
 
+        self._used_interpreter = None
+
     @abstractmethod
     def run(self, tmp=None, task_vars=None):
         """ Action Plugins should implement this method to perform their
@@ -753,6 +755,7 @@ def _execute_module(self, module_name=None, module_args=None, tmp=None, task_var
         if not shebang and module_style != 'binary':
             raise AnsibleError("module (%s) is missing interpreter line" % module_name)
 
+        self._used_interpreter = shebang
         remote_module_path = None
 
         if not self._is_pipelining_enabled(module_style, wrap_async):
@@ -896,12 +899,20 @@ def _parse_returned_data(self, res):
         except ValueError:
             # not valid json, lets try to capture error
             data = dict(failed=True, _ansible_parsed=False)
-            data['msg'] = "MODULE FAILURE"
             data['module_stdout'] = res.get('stdout', u'')
             if 'stderr' in res:
                 data['module_stderr'] = res['stderr']
                 if res['stderr'].startswith(u'Traceback'):
                     data['exception'] = res['stderr']
+
+            # try to figure out if we are missing interpreter
+            if self._used_interpreter is not None and '%s: No such file or directory' % self._used_interpreter.lstrip('!#') in data['module_stderr']:
+                data['msg'] = "The module failed to execute correctly, you probably need to set the interpreter."
+            else:
+                data['msg'] = "MODULE FAILURE"
+
+            data['msg'] += '\nSee stdout/stderr for the exact error'
+
             if 'rc' in res:
                 data['rc'] = res['rc']
         return data