Allow subcommands to accept --help when using 'deferred_help'.

This patch changes how cliff handles help for subcommands but only when
'deferred_help' is enabled. Currently cliff consumes --help requests at the top
level. This means `myapp foo --help` and `myapp --help` produce the same output.
To get help for `foo` one must use `myapp help foo`. With this change
`myapp foo --help` will produce the same output as `myapp help foo` by
transforming the --help request into a help subcommand one. This is only done
when there are any options on the command line other than --help. When a top
level --help is requested the original behavior of print_help_if_requested()
is preserved.

Change-Id: I628bbfc383de516045288512cc023213d723a027
Closes-Bug: 1444983

cliff/app.py

@@ -221,6 +221,18 @@ class App(object):
             self.options, remainder = self.parser.parse_known_args(argv)
             self.configure_logging()
             self.interactive_mode = not remainder
+            if self.deferred_help and self.options.deferred_help and remainder:
+                # When help is requested and `remainder` has any values disable
+                # `deferred_help` and instead allow the help subcommand to
+                # handle the request during run_subcommand(). This turns
+                # "app foo bar --help" into "app help foo bar". However, when
+                # `remainder` is empty use print_help_if_requested() to allow
+                # for an early exit.
+                # Disabling `deferred_help` here also ensures that
+                # print_help_if_requested will not fire if called by a subclass
+                # during its initialize_app().
+                self.options.deferred_help = False
+                remainder.insert(0, "help")
             self.initialize_app(remainder)
             self.print_help_if_requested()
         except Exception as err:

cliff/tests/test_app.py

@@ -401,6 +401,26 @@ def test_deferred_help():
     _test_help(True)
 
 
+def test_subcommand_help():
+    app, _ = make_app(deferred_help=False)
+
+    # Help is called immediately
+    with mock.patch('cliff.help.HelpAction.__call__') as helper:
+        app.run(['show', 'files', '--help'])
+
+    assert helper.called
+
+
+def test_subcommand_deferred_help():
+    app, _ = make_app(deferred_help=True)
+
+    # Show that provide_help_if_requested() did not show help and exit
+    with mock.patch.object(app, 'run_subcommand') as helper:
+        app.run(['show', 'files', '--help'])
+
+    helper.assert_called_once_with(['help', 'show', 'files'])
+
+
 def test_unknown_cmd():
     app, command = make_app()
     assert app.run(['hell']) == 2