diff --git a/doc/source/command-wrappers.rst b/doc/source/command-wrappers.rst new file mode 100644 index 0000000000..b14eccdde8 --- /dev/null +++ b/doc/source/command-wrappers.rst @@ -0,0 +1,52 @@ +====================== +Command Class Wrappers +====================== + +When we want to deprecate a command, policy says we need to alert the user. +We do this with a message logged at WARNING level before any command output +is emitted. + +OpenStackClient command classes are derived from the ``cliff`` classes. +Cliff uses ``setuptools`` entry points for dispatching the parsed command +to the respective handler classes. This lends itself to modifying the +command execution at run-time. + +The obvious approach to adding the deprecation message would be to just add +the message to the command class ``take_action()`` method directly. But then +the various deprecations are scattered throughout the code base. If we +instead wrap the deprecated command class with a new class we can put all of +the wrappers into a separate, dedicated module. This also lets us leave the +original class unmodified and puts all of the deprecation bits in one place. + +This is an example of a minimal wrapper around a command class that logs a +deprecation message as a warning to the user then calls the original class. + +* Subclass the deprecated command. + +* Set class attribute ``deprecated`` to ``True`` to signal cliff to not + emit help text for this command. + +* Log the deprecation message at WARNING level and refer to the replacement + for the deprecated command in the log warning message. + +* Change the entry point class in ``setup.cfg`` to point to the new class. + +Example Deprecation Class +------------------------- + +.. code-block: python + + class ListFooOld(ListFoo): + """List resources""" + + # This notifies cliff to not display the help for this command + deprecated = True + + log = logging.getLogger('deprecated') + + def take_action(self, parsed_args): + self.log.warning( + "%s is deprecated, use 'foobar list'", + getattr(self, 'cmd_name', 'this command'), + ) + return super(ListFooOld, self).take_action(parsed_args) diff --git a/doc/source/index.rst b/doc/source/index.rst index 50b1fd24a6..66afc2b5d0 100644 --- a/doc/source/index.rst +++ b/doc/source/index.rst @@ -38,6 +38,7 @@ Developer Documentation developing command-options + command-wrappers Project Goals -------------