move print output from repo/diff.py to command/diff.py and minor fixes in command/diff.py

dvc/command/diff.py

@@ -1,13 +1,29 @@
 from __future__ import unicode_literals
 
+import dvc.logger as logger
+from dvc.exceptions import DvcException
 from dvc.command.base import CmdBase
 
 
-class CmdMove(CmdBase):
+class CmdDiff(CmdBase):
+    def _show(self, msg):
+        logger.info(msg)
+
     def run(self):
-        self.repo.diff(
-            self.args.target, a_ref=self.args.a_ref, b_ref=self.args.b_ref
-        )
+        try:
+            msg = self.repo.diff(
+                self.args.target, a_ref=self.args.a_ref, b_ref=self.args.b_ref
+            )
+            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 + " "
+            logger.error(msg)
         return 0
 
 
@@ -33,4 +49,4 @@ def add_parser(subparsers, parent_parser):
         nargs="?",
         default=None,
     )
-    diff_parser.set_defaults(func=CmdMove)
+    diff_parser.set_defaults(func=CmdDiff)

dvc/repo/diff.py

@@ -1,8 +1,6 @@
 import os
 import math
 
-import dvc.logger as logger
-
 
 def _extract_tree(self, cache_dir):
     lst = self.cache.local.load_dir_cache(cache_dir)
@@ -123,7 +121,6 @@ def diff(self, target, a_ref=None, b_ref=None):
         target, diff_dct["a_tag"], diff_dct["b_tag"]
     )
     if diff_dct["equal"]:
-        logger.info(msg)
         return msg
     if diff_dct["is_dir"]:
         dir_info = _diff_dir(self, target, diff_dct)
@@ -131,5 +128,4 @@ def diff(self, target, a_ref=None, b_ref=None):
     else:
         file_info = _diff_file(self, target, diff_dct)
         msg += file_info
-    logger.info(msg)
     return msg