Deny creating subdirectories

Currently if we put a path separator in slug, "reno new" command
creates subdirectories under the notes subdirectory. This usually
results in the situation where the note file is put to an unexpected
place.
For example we have seen several cases with reno files placed under
releasenote/notes/releasenote/notes directory because the notes
subdirectory path is accidentally included in slug, like;

$ reno new releasenotes/notes/something-new
no configuration file in: ./releasenotes/config.yaml, ./reno.yaml
Created new notes file in releasenotes/notes/releasenotes/notes/something-new-2ff053c99583fc69.yaml

This change prohibits users from creating such subdirectries under
the notes subdirectory. The previous behavior can be restored by
the allow_subdirectories config option.

Change-Id: I30b5de3d5f35abb3b903e9ed9e4db42671421e88

reno/config.py

@@ -31,6 +31,11 @@ _OPTIONS = [
         notes live.
         """)),
 
+    Opt('allow_subdirectories', False,
+        textwrap.dedent("""\
+        Allow creating subdirectories under the notes subdirectory.
+        """)),
+
     Opt('collapse_pre_releases', True,
         textwrap.dedent("""\
         Should pre-release versions be merged into the final release

reno/create.py

@@ -64,6 +64,11 @@ def create_cmd(args, conf):
     # their local git tree, and so there should not be any concurrency
     # concern.
     slug = args.slug.replace(' ', '-')
+
+    if not conf.options['allow_subdirectories'] and os.sep in slug:
+        raise ValueError('Slug should not include the path separator (%s)'
+                         % os.sep)
+
     filename = _pick_note_file_name(conf.notespath, slug)
     encoding = conf.options['encoding']
     if args.from_template:

reno/tests/test_create.py

@@ -16,6 +16,7 @@ from unittest import mock
 
 import fixtures
 import io
+import os
 
 from reno import config
 from reno import create
@@ -72,7 +73,7 @@ class TestCreate(base.TestCase):
         args.edit = False
         conf = mock.create_autospec(config.Config)
         conf.notespath = self.tmpdir
-        conf.options = {'encoding': None}
+        conf.options = {'allow_subdirectories': False, 'encoding': None}
         with mock.patch('sys.stdout', new=io.StringIO()) as fake_out:
             create.create_cmd(args, conf)
         filename = self._get_file_path_from_output(fake_out.getvalue())
@@ -87,8 +88,34 @@ class TestCreate(base.TestCase):
         args.edit = False
         conf = mock.create_autospec(config.Config)
         conf.notespath = self.tmpdir
+        conf.options = {'allow_subdirectories': False, 'encoding': None}
         self.assertRaises(ValueError, create.create_cmd, args, conf)
 
+    def test_create_from_user_template_fails_because_path_separator(self):
+        args = mock.Mock()
+        args.from_template = self._create_user_template('i-am-a-user-template')
+        args.slug = 'the' + os.sep + 'slug'
+        args.edit = False
+        conf = mock.create_autospec(config.Config)
+        conf.notespath = self.tmpdir
+        conf.options = {'allow_subdirectories': False, 'encoding': None}
+        self.assertRaises(ValueError, create.create_cmd, args, conf)
+
+    def test_create_from_template_with_path_separator_allowed(self):
+        args = mock.Mock()
+        args.from_template = self._create_user_template('i-am-a-user-template')
+        args.slug = 'the' + os.sep + 'slug'
+        args.edit = False
+        conf = mock.create_autospec(config.Config)
+        conf.notespath = self.tmpdir
+        conf.options = {'allow_subdirectories': True, 'encoding': None}
+        with mock.patch('sys.stdout', new=io.StringIO()) as fake_out:
+            create.create_cmd(args, conf)
+        filename = self._get_file_path_from_output(fake_out.getvalue())
+        with open(filename, 'r') as f:
+            body = f.read()
+        self.assertEqual('i-am-a-user-template', body)
+
     def test_edit(self):
         self.useFixture(fixtures.EnvironmentVariable('EDITOR', 'myeditor'))
         with mock.patch('subprocess.call') as call_mock: