Allow tracking empty directories

Handle creating and removing placeholders files for versioning empty
directories as suggested in [1].

[1]: https://git.wiki.kernel.org/index.php/GitFaq#Can_I_add_empty_directories.3F

Author: embs

gitless/cli/file_cmd.py

@@ -7,6 +7,8 @@
 
 from __future__ import unicode_literals
 
+from gitless import core
+
 from . import helpers, pprint
 
 
@@ -35,11 +37,16 @@ def f(args, repo):
 
     for fp in args.files:
       try:
+        empty_dir = fp.endswith(core.GL_KEEP_FILENAME)
         getattr(curr_b, subcmd + '_file')(fp)
+        if empty_dir:
+          fp = fp.replace(core.GL_KEEP_FILENAME, '')
         pprint.ok(
-            'File {0} is now a{1} {2}{3}d file'.format(
+            '{0} {1} is now a{2} {3}{4}d {5}'.format(
+              'Empty directory' if empty_dir else 'File',
               fp, 'n' if subcmd.startswith(VOWELS) else '', subcmd,
-              '' if subcmd.endswith('e') else 'e'))
+              '' if subcmd.endswith('e') else 'e',
+              'directory' if empty_dir else 'file'))
       except KeyError:
         pprint.err('Can\'t {0} non-existent file {1}'.format(subcmd, fp))
         success = False

gitless/cli/helpers.py

@@ -129,6 +129,9 @@ def process_paths():
                 self.skip_dir_cb(curr_dir_rel)
               dirs[:] = []
               continue
+            if not fps:
+              open(os.path.join(curr_dir, core.GL_KEEP_FILENAME), 'a').close()
+              fps.append(core.GL_KEEP_FILENAME)
             for fp in fps:
               yield os.path.join(curr_dir_rel, fp)
         else:

gitless/core.py

@@ -54,6 +54,8 @@ class ApplyFailedError(GlError): pass
 GL_STATUS_TRACKED = 2
 GL_STATUS_IGNORED = 3
 
+GL_KEEP_FILENAME = '.glkeep'
+
 
 def init_repository(url=None):
   """Creates a new Gitless's repository in the cwd.

gitless/tests/test_e2e.py

@@ -683,6 +683,20 @@ def test_uncommitted_tracked_changes_that_conflict_append(self):
     self.assertTrue('contents 2' in contents)
 
 
+class TestEmptyDir(TestEndToEnd):
+
+  def test_track_empty_dir(self):
+    dir_to_track = 'wanted_empty_dir'
+    dir_to_track_path = os.path.join(self.path, dir_to_track)
+    os.mkdir(dir_to_track_path)
+    expected_out = 'Empty directory {0} is now a tracked directory'.format(
+      os.path.join(dir_to_track, ''))
+
+    out = utils.stdout(gl.track(dir_to_track_path))
+
+    self.assertIn(expected_out, out, 'Empty dir wasn\'t tracked')
+
+
 class TestPerformance(TestEndToEnd):
 
   FPS_QTY = 10000