output: base: don't forget to return empty cache (#2656)

* output: base: don't forget to return empty cache

CC @Suor

Fixes https://gist.github.com/leimbernon/21924e02a998e3f1604990f8a7824c37

Signed-off-by: Ruslan Kuprieiev <[email protected]>

* gc: add test for missing .dir cache file

dvc/exceptions.py

@@ -325,3 +325,7 @@ class CheckoutError(DvcException):
             "forget to fetch?".format("\n".join(targets))
         )
         super(CheckoutError, self).__init__(m)
+
+
+class CollectCacheError(DvcException):
+    pass

dvc/output/base.py

@@ -7,7 +7,7 @@ from schema import Or, Optional
 
 from dvc.cache import NamedCache
 import dvc.prompt as prompt
-from dvc.exceptions import DvcException
+from dvc.exceptions import DvcException, CollectCacheError
 from dvc.utils.compat import str, urlparse
 from dvc.remote.base import RemoteBASE
 
@@ -353,7 +353,7 @@ class OutputBase(object):
             nc.add(self.scheme, 'd3b07384d113', 'directory/bar')
         """
 
-        ret = []
+        cache = NamedCache()
 
         if self.cache.changed_cache_file(self.checksum):
             try:
@@ -373,14 +373,13 @@ class OutputBase(object):
                 "Would you like to continue? Use '-f' to force."
             )
             if not force and not prompt.confirm(msg.format(self.path_info)):
-                raise DvcException(
+                raise CollectCacheError(
                     "unable to fully collect used cache"
                     " without cache for directory '{}'".format(self)
                 )
             else:
-                return ret
+                return cache
 
-        cache = NamedCache()
         for entry in self.dir_cache:
             checksum = entry[self.remote.PARAM_CHECKSUM]
             path_info = self.path_info / entry[self.remote.PARAM_RELPATH]

tests/func/test_gc.py

@@ -1,5 +1,7 @@
 from __future__ import unicode_literals
 import os
+
+import pytest
 import configobj
 
 from git import Repo
@@ -7,6 +9,7 @@ from git import Repo
 from dvc.utils.compat import pathlib
 from dvc.main import main
 from dvc.repo import Repo as DvcRepo
+from dvc.exceptions import CollectCacheError
 
 from tests.basic_env import TestDvcGit
 from tests.basic_env import TestDir
@@ -208,3 +211,20 @@ def test_all_commits(git, dvc_repo):
 
 def _count_files(path):
     return sum(len(files) for _, _, files in os.walk(path))
+
+
+def test_gc_no_dir_cache(repo_dir, dvc_repo):
+    dvc_repo.add(repo_dir.FOO)
+    dvc_repo.add(repo_dir.BAR)
+    dir_stage, = dvc_repo.add(repo_dir.DATA_DIR)
+
+    os.unlink(dir_stage.outs[0].cache_path)
+
+    with pytest.raises(CollectCacheError):
+        dvc_repo.gc()
+
+    assert _count_files(dvc_repo.cache.local.cache_dir) == 4
+
+    dvc_repo.gc(force=True)
+
+    assert _count_files(dvc_repo.cache.local.cache_dir) == 2