dvc: change help output of diff command and minor fixes

dvc/command/diff.py

@@ -3,6 +3,7 @@ from __future__ import unicode_literals
 import dvc.logger as logger
 from dvc.exceptions import DvcException
 from dvc.command.base import CmdBase
+from dvc.utils.collections import compact
 
 
 class CmdDiff(CmdBase):
@@ -16,20 +17,18 @@ class CmdDiff(CmdBase):
             )
             self._show(msg)
         except DvcException:
-            msg = "failed to get diff "
-            if self.args.target:
-                msg += self.args.target + " "
-            if self.args.a_ref:
-                msg += self.args.a_ref + " "
-            if self.args.b_ref:
-                msg += self.args.b_ref + " "
+            msg = "failed to get 'diff "
+            msg += " ".join(
+                compact([self.args.target, self.args.a_ref, self.args.b_ref])
+            )
+            msg += "'"
             logger.error(msg)
         return 0
 
 
 def add_parser(subparsers, parent_parser):
     description = (
-        "show diff of a data file or a directory that "
+        "Show diff of a data file or a directory that "
         "is under DVC control. Some basic statistics "
         "summary, how many files were deleted/changed."
     )
@@ -43,7 +42,8 @@ def add_parser(subparsers, parent_parser):
         default=None,
         help=(
             "Source path to a data file or directory. Default None,"
-            "if None shows the diff between all DVC tracked files/directories"
+            "If not specified, compares all files and directories "
+            "that are under DVC control in the current working space."
         ),
     )
     diff_parser.add_argument(

dvc/repo/diff.py

@@ -8,7 +8,15 @@ import inflect
 from dvc.scm.base import FileNotInCommitError
 
 
-def _extract_output(self, output):
+def _extract_dir(self, output):
+    """Extract the content of dvc tree file
+    Args:
+        self(object) - Repo class instance
+        output(object) - OutputLOCAL class instance
+    Returns:
+        dict - dictionary with keys - paths to file in .dvc/cache
+                               values -checksums for that files
+    """
     lst = output.dir_cache
     return {i["relpath"]: i["md5"] for i in lst}
 
@@ -81,12 +89,12 @@ def _diff_dir(self, target, diff_dct):
         msg += "-{} with md5 {}\n".format(
             target, diff_dct["a_output"].checksum
         )
-        a_entries = _extract_output(self, diff_dct["a_output"])
+        a_entries = _extract_dir(self, diff_dct["a_output"])
     if not diff_dct["deleted_file"]:
         msg += "+{} with md5 {}\n".format(
             target, diff_dct["b_output"].checksum
         )
-        b_entries = _extract_output(self, diff_dct["b_output"])
+        b_entries = _extract_dir(self, diff_dct["b_output"])
     msg += "\n"
     result = _get_tree_changes(self, a_entries, b_entries)
     msg += f"{result['ident']} " + engine.plural("file", result["ident"])
@@ -139,9 +147,9 @@ def _diff_file(self, target, diff_dct):
 
 
 def _diff_royal(self, target, diff_dct):
-    msg = "diff for " + target + "\n"
+    msg = "diff for '" + target + "'\n"
     if diff_dct["is_dir"]:
-        return _diff_dir(self, target, diff_dct)
+        return msg + _diff_dir(self, target, diff_dct)
     return msg + _diff_file(self, target, diff_dct)
 
 

dvc/scm/git/__init__.py

@@ -236,15 +236,14 @@ class Git(Base):
     def get_tree(self, rev):
         return GitTree(self.git, rev)
 
-    def _get_diff_trees(self, a_ref, **kwargs):
+    def _get_diff_trees(self, a_ref, b_ref):
 
         from gitdb.exc import BadObject, BadName
 
         trees = {"a_tree": None, "b_tree": None}
         commits = []
         try:
-            if "b_ref" in kwargs and kwargs["b_ref"] is not None:
-                b_ref = kwargs["b_ref"]
+            if b_ref is not None:
                 a_commit = self.git.commit(a_ref)
                 b_commit = self.git.commit(b_ref)
                 commits.append(str(a_commit))
@@ -263,7 +262,7 @@ class Git(Base):
             raise SCMError("git problem", cause=e)
         return trees, commits
 
-    def get_diff_trees(self, a_ref, **kwargs):
+    def get_diff_trees(self, a_ref, b_ref=None):
         """Method for getting two repo trees between two git tag commits
         returns the dvc hash names of changed file/directory
 
@@ -275,7 +274,7 @@ class Git(Base):
             dict - dictionary with keys: (a_tree, b_tree, a_ref, b_ref, equal)
         """
         diff_dct = {"equal": False}
-        trees, commit_refs = self._get_diff_trees(a_ref, **kwargs)
+        trees, commit_refs = self._get_diff_trees(a_ref, b_ref)
         diff_dct["a_ref"] = commit_refs[0]
         diff_dct["b_ref"] = commit_refs[1]
         if commit_refs[0] == commit_refs[1]:

dvc/utils/collections.py

@@ -0,0 +1,6 @@
+from __future__ import unicode_literals
+
+
+# just simple check for Nones and emtpy strings
+def compact(args):
+    return list(filter(bool, args))

setup.py

@@ -23,6 +23,8 @@ install_requires = [
     "distro>=1.3.0",
     "appdirs>=1.4.3",
     "treelib>=1.5.5",
+    "inflect>=2.1.0",
+    "humanize>=0.5.1",
 ]
 
 # Extra dependencies for remote integrations

tests/test_diff.py

@@ -35,7 +35,7 @@ class TestDiffRepo(TestDiff):
         new_ref = self.git.head.commit
         msg = self.dvc.diff(self.new_file, a_ref=self.a_ref)
         test_msg = "dvc diff from {} to {}\n\n".format(new_ref, self.a_ref)
-        test_msg += "diff for {}\n".format(self.new_file)
+        test_msg += "diff for '{}'\n".format(self.new_file)
         test_msg += "-new_file with md5 25fa8325e4e0eb8180445e42558e60bd\n"
         test_msg += "deleted file with size -8 Bytes"
         self.assertEqual(test_msg, msg)
@@ -77,6 +77,7 @@ class TestDiffDirRepo(TestDiffDir):
         msg = self.dvc.diff(self.DATA_DIR, a_ref=self.a_ref)
         test_msg = "dvc diff from ".format(self.DATA_DIR)
         test_msg += "{} to {}\n\n".format(new_ref, self.a_ref)
+        test_msg += "diff for '{}'\n".format(self.DATA_DIR)
         test_msg += "-data_dir with md5 d5782f3072167ad3a53ee80b92b30718.dir\n"
         test_msg += (
             "+data_dir with md5 bff5a787d16460f32e9f2e62b183b1cc.dir\n\n"