Add support for loading external plugins from directory.

Create new option --plugins to pass a directory for loading external plugins.
Also, add some plugins examples in examples/avocado_example_plugins.py.

The external plugins are loaded from avocado_*.py modules and the plugins are
subclasses of Plugin().
Signed-off-by: NRuda Moura <rmoura@redhat.com>

avocado/cli/app.py

@@ -26,17 +26,26 @@ class AvocadoApp(object):
         self.arg_parser.add_argument('--loglevel', action='store',
                                      help='Debug Level',
                                      dest='log_level', default='')
+        self.arg_parser.add_argument('--plugins', action='store',
+                                     help='Load extra plugins from directory',
+                                     dest='plugins_dir', default='')
 
+        args, extra = self.arg_parser.parse_known_args()
         subparsers = self.arg_parser.add_subparsers(title='subcommands',
                                                     description='valid subcommands',
                                                     help='subcommand help')
 
-        self.load_plugin_manager(subparsers)
+        self.load_plugin_manager(subparsers, args.plugins_dir)
         self.args = self.arg_parser.parse_args()
 
-    def load_plugin_manager(self, parser):
+    def load_plugin_manager(self, parser, plugins_dir):
+        """Load Plugin Manager.
+
+        :param parser: Main argument parser.
+        :param plugins_dir: Extra plugins directory.
+        """
         self.plugin_manager = get_plugin_manager()
-        self.plugin_manager.load_plugins()
+        self.plugin_manager.load_plugins(plugins_dir)
         if self.external_plugins:
             self.plugin_manager.add_plugins(self.external_plugins)
         self.plugin_manager.configure(parser)

avocado/plugins/manager.py

 """Plugin Managers."""
 
 from avocado.plugins.builtin import load_builtins
+from avocado.plugins.plugin import Plugin
 
 DefaultPluginManager = None
 
@@ -23,7 +24,8 @@ class PluginManager(object):
         raise NotImplementedError('Managers must implement the method load_plugins')
 
     def configure(self, parser):
-        raise NotImplementedError('Managers must implement the method configure')
+        for plugin in self.plugins:
+            plugin.configure(parser)
 
 
 class BuiltinPluginManager(PluginManager):
@@ -36,10 +38,6 @@ class BuiltinPluginManager(PluginManager):
         for plugin in load_builtins():
             self.add_plugin(plugin())
 
-    def configure(self, parser):
-        for plugin in self.plugins:
-            plugin.configure(parser)
-
 
 class ExternalPluginManager(PluginManager):
 
@@ -47,6 +45,21 @@ class ExternalPluginManager(PluginManager):
     Load external plugins.
     """
 
+    def load_plugins(self, path, pattern='avocado_*.py'):
+        from glob import glob
+        import os
+        import imp
+        if path:
+            candidates = glob(os.path.join(path, pattern))
+            candidates = [(os.path.splitext(os.path.basename(x))[0], path) for x in candidates]
+            candidates = [(x[0], imp.find_module(x[0], [path])) for x in candidates]
+            for candidate in candidates:
+                mod = imp.load_module(candidate[0], *candidate[1])
+                for name in mod.__dict__:
+                    x = getattr(mod, name)
+                    if isinstance(x, type) and issubclass(x, Plugin):
+                        self.add_plugin(x())
+
     def add_plugins(self, plugins):
         for plugin in plugins:
             self.add_plugin(plugin)
@@ -60,6 +73,13 @@ class AvocadoPluginManager(BuiltinPluginManager, ExternalPluginManager):
     Load builtins and external plugins.
     """
 
+    def __init__(self):
+        BuiltinPluginManager.__init__(self)
+        ExternalPluginManager.__init__(self)
+
+    def load_plugins(self, path=None):
+        BuiltinPluginManager.load_plugins(self)
+        ExternalPluginManager.load_plugins(self, path)
 
 def get_plugin_manager():
     """

examples/avocado_example_plugins.py

+from avocado.plugins import plugin
+from avocado.plugins.manager import get_plugin_manager
+from avocado.core import output
+
+class HelloWorld(plugin.Plugin):
+
+    """
+    Hello World! plugin example.
+    """
+
+    def configure(self, parser):
+        myparser = parser.add_parser('hello',
+                                     help='Hello World! plugin example')
+        myparser.set_defaults(func=self.hello)
+        self.enabled = True
+
+    def hello(self, args):
+        print self.__doc__
+
+
+class PluginsList(plugin.Plugin):
+
+    """
+    List all plugins loaded.
+    """
+
+    def configure(self, parser):
+        myparser = parser.add_parser('plugins',
+                                     help='List all plugins loaded')
+        myparser.set_defaults(func=self.list_plugins)
+        self.enabled = True
+
+    def list_plugins(self, args):
+        bcolors = output.colors
+        pipe = output.get_paginator()
+        pm = get_plugin_manager()
+        pipe.write(bcolors.header_str('Plugins loaded:'))
+        pipe.write('\n')
+        for plug in pm.plugins:
+            pipe.write('    %s - %s\n' % (plug, plug.__doc__))