Graceful error message for abstract base classes in PluginLoader

lib/ansible/plugins/__init__.py

@@ -31,7 +31,6 @@ import warnings
 from collections import defaultdict
 
 from ansible import constants as C
-from ansible.compat.six import string_types
 from ansible.module_utils._text import to_text
 
 
@@ -370,7 +369,14 @@ class PluginLoader:
         self._display_plugin_load(self.class_name, name, self._searched_paths, path,
                                   found_in_cache=found_in_cache, class_only=class_only)
         if not class_only:
-            obj = obj(*args, **kwargs)
+            try:
+                obj = obj(*args, **kwargs)
+            except TypeError as e:
+                if "abstract" in e.args[0]:
+                    # Abstract Base Class.  The found plugin file does not
+                    # fully implement the defined interface.
+                    return None
+                raise
 
         return obj
 
@@ -430,7 +436,10 @@ class PluginLoader:
             self._display_plugin_load(self.class_name, name, self._searched_paths, path,
                                       found_in_cache=found_in_cache, class_only=class_only)
             if not class_only:
-                obj = obj(*args, **kwargs)
+                try:
+                    obj = obj(*args, **kwargs)
+                except TypeError as e:
+                    display.warning("Skipping plugin (%s) as it seems to be incomplete: %s" % (path, to_text(e)))
 
             # set extra info on the module, in case we want it later
             setattr(obj, '_original_path', path)