Allow finding command by partial name

This small improvement helps to decrease the amount of typing.

$ openstack resource provider list
...
^ too long?

$ alias os=openstack
$ os r p l
...
^ much better!

Change-Id: I713eab2bd9f949da01c03b65ff16a01de92e3e62

cliff/commandmanager.py

@@ -22,6 +22,18 @@ import pkg_resources
 LOG = logging.getLogger(__name__)
 
 
+def _get_commands_by_partial_name(args, commands):
+    n = len(args)
+    candidates = []
+    for command_name in commands:
+        command_parts = command_name.split()
+        if len(command_parts) != n:
+            continue
+        if all(command_parts[i].startswith(args[i]) for i in range(n)):
+            candidates.append(command_name)
+    return candidates
+
+
 class EntryPointWrapper(object):
     """Wrap up a command class already imported to make it look like a plugin.
     """
@@ -96,8 +108,17 @@ class CommandManager(object):
             # Convert the legacy command name to its new name.
             if name in self._legacy:
                 name = self._legacy[name]
+
+            found = None
             if name in self.commands:
-                cmd_ep = self.commands[name]
+                found = name
+            else:
+                candidates = _get_commands_by_partial_name(
+                    argv[:i], self.commands)
+                if len(candidates) == 1:
+                    found = candidates[0]
+            if found:
+                cmd_ep = self.commands[found]
                 if hasattr(cmd_ep, 'resolve'):
                     cmd_factory = cmd_ep.resolve()
                 else:

cliff/tests/test_commandmanager.py

@@ -199,3 +199,57 @@ class TestLegacyCommand(base.TestBase):
             mgr.find_command,
             ['cmd2'],
         )
+
+
+class TestLookupAndFindPartialName(base.TestBase):
+
+    scenarios = [
+        ('one-word', {'argv': ['o']}),
+        ('two-words', {'argv': ['t', 'w']}),
+        ('three-words', {'argv': ['t', 'w', 'c']}),
+    ]
+
+    def test(self):
+        mgr = utils.TestCommandManager(utils.TEST_NAMESPACE)
+        cmd, name, remaining = mgr.find_command(self.argv)
+        self.assertTrue(cmd)
+        self.assertEqual(' '.join(self.argv), name)
+        self.assertFalse(remaining)
+
+
+class TestGetByPartialName(base.TestBase):
+
+    def setUp(self):
+        super(TestGetByPartialName, self).setUp()
+        self.commands = {
+            'resource provider list': 1,
+            'resource class list': 2,
+            'server list': 3,
+            'service list': 4}
+
+    def test_no_candidates(self):
+        self.assertEqual(
+            [], commandmanager._get_commands_by_partial_name(
+                ['r', 'p'], self.commands))
+        self.assertEqual(
+            [], commandmanager._get_commands_by_partial_name(
+                ['r', 'p', 'c'], self.commands))
+
+    def test_multiple_candidates(self):
+        self.assertEqual(
+            2, len(commandmanager._get_commands_by_partial_name(
+                ['se', 'li'], self.commands)))
+
+    def test_one_candidate(self):
+        self.assertEqual(
+            ['resource provider list'],
+            commandmanager._get_commands_by_partial_name(
+                ['r', 'p', 'l'], self.commands))
+        self.assertEqual(
+            ['resource provider list'],
+            commandmanager._get_commands_by_partial_name(
+                ['resource', 'provider', 'list'], self.commands))
+        self.assertEqual(
+            ['server list'],
+            commandmanager._get_commands_by_partial_name(
+                ['serve', 'l'], self.commands))