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-rw-r--r--doc/source/command-wrappers.rst52
-rw-r--r--doc/source/index.rst1
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diff --git a/doc/source/command-wrappers.rst b/doc/source/command-wrappers.rst
new file mode 100644
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@@ -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 50b1fd24..66afc2b5 100644
--- a/doc/source/index.rst
+++ b/doc/source/index.rst
@@ -38,6 +38,7 @@ Developer Documentation
developing
command-options
+ command-wrappers
Project Goals
-------------