make help list commands if none match exactly; fixes #8

3 files changed, 60 insertions, 1 deletions

diff --git a/cliff/help.py b/cliff/help.py
index 2ac8bc4..1e4793e 100644
--- a/cliff/help.py
+++ b/cliff/help.py
@@ -38,7 +38,20 @@ class HelpCommand(Command):
 
     def run(self, parsed_args):
         if parsed_args.cmd:
-            cmd_factory, cmd_name, search_args = self.app.command_manager.find_command(parsed_args.cmd)
+            try:
+                cmd_factory, cmd_name, search_args = self.app.command_manager.find_command(parsed_args.cmd)
+            except ValueError:
+                # Did not find an exact match
+                cmd = parsed_args.cmd[0]
+                fuzzy_matches = [k[0] for k in self.app.command_manager
+                                 if k[0].startswith(cmd)
+                                 ]
+                if not fuzzy_matches:
+                    raise
+                self.app.stdout.write('Command "%s" matches:\n' % cmd)
+                for fm in fuzzy_matches:
+                    self.app.stdout.write('  %s\n' % fm)
+                return
             cmd = cmd_factory(self.app, search_args)
             full_name = (cmd_name
                          if self.app.interactive_mode
diff --git a/docs/source/history.rst b/docs/source/history.rst
index bb3eb54..5b233b8 100644
--- a/docs/source/history.rst
+++ b/docs/source/history.rst
@@ -2,6 +2,11 @@
  Release History
 =================
 
+dev
+
+  - Asking for help about a command by prefix lists all matching
+    commands.
+
 0.4
 
   - Add shell formatter for single objects.
diff --git a/tests/test_help.py b/tests/test_help.py
index 4a2fd1c..8c7e7ed 100644
--- a/tests/test_help.py
+++ b/tests/test_help.py
@@ -57,6 +57,47 @@ def test_show_help_for_command():
         pass
     assert stdout.getvalue() == 'TestParser'
 
+
+def test_list_matching_commands():
+    # FIXME(dhellmann): Are commands tied too closely to the app? Or
+    # do commands know too much about apps by using them to get to the
+    # command manager?
+    stdout = StringIO()
+    app = App('testing', '1', TestCommandManager('cliff.test'), stdout=stdout)
+    app.NAME = 'test'
+    help_cmd = HelpCommand(app, mock.Mock())
+    parser = help_cmd.get_parser('test')
+    parsed_args = parser.parse_args(['t'])
+    try:
+        help_cmd.run(parsed_args)
+    except SystemExit:
+        pass
+    help_output = stdout.getvalue()
+    assert 'Command "t" matches:' in help_output
+    assert 'two' in help_output
+    assert 'three' in help_output
+
+
+def test_list_matching_commands_no_match():
+    # FIXME(dhellmann): Are commands tied too closely to the app? Or
+    # do commands know too much about apps by using them to get to the
+    # command manager?
+    stdout = StringIO()
+    app = App('testing', '1', TestCommandManager('cliff.test'), stdout=stdout)
+    app.NAME = 'test'
+    help_cmd = HelpCommand(app, mock.Mock())
+    parser = help_cmd.get_parser('test')
+    parsed_args = parser.parse_args(['z'])
+    try:
+        help_cmd.run(parsed_args)
+    except SystemExit:
+        pass
+    except ValueError:
+        pass
+    else:
+        assert False, 'Should have seen a ValueError'
+
+
 def test_show_help_for_help():
     # FIXME(dhellmann): Are commands tied too closely to the app? Or
     # do commands know too much about apps by using them to get to the