fail silently but with a more sound error message

* Add a `_missing` key to the return value of `repo.metrics.show` to
include targets not recognized as metrics or not found.

dvc/command/metrics.py

@@ -2,9 +2,8 @@ from __future__ import unicode_literals
 
 import argparse
 import logging
-import itertools
 
-from dvc.exceptions import DvcException
+from dvc.exceptions import DvcException, BadMetricError
 from dvc.command.base import CmdBase, fix_subparsers, append_doc_link
 
 
@@ -17,6 +16,10 @@ def show_metrics(metrics, all_branches=False, all_tags=False):
         metrics (list): Where each element is either a `list`
             if an xpath was specified, otherwise a `str`
     """
+    # When `metrics` contains a `_missing` key, it means that some files
+    # specified as `targets` in `repo.metrics.show` didn't contain any metrics.
+    missing = metrics.pop("_missing", None)
+
     for branch, val in metrics.items():
         if all_branches or all_tags:
             logger.info("{branch}:".format(branch=branch))
@@ -33,6 +36,9 @@ def show_metrics(metrics, all_branches=False, all_tags=False):
             else:
                 logger.info("\t{}: {}".format(fname, metric))
 
+    if missing:
+        raise BadMetricError(missing)
+
 
 class CmdMetricsShow(CmdBase):
     def run(self):
@@ -47,24 +53,6 @@ class CmdMetricsShow(CmdBase):
             )
 
             show_metrics(metrics, self.args.all_branches, self.args.all_tags)
-
-            found = set(
-                itertools.chain.from_iterable(
-                    metric.keys() for metric in metrics.values()
-                )
-            )
-
-            missing = set(self.args.targets) - found
-
-            if missing:
-                logger.error(
-                    "the following metrics do not exists, "
-                    "are not metric files or are malformed: {paths}".format(
-                        paths=", ".join("'{}'".format(x) for x in missing)
-                    )
-                )
-                return 1
-
         except DvcException:
             logger.exception("failed to show metrics")
             return 1

dvc/exceptions.py

@@ -195,6 +195,16 @@ class ReproductionError(DvcException):
         super(ReproductionError, self).__init__(msg, cause=ex)
 
 
+class BadMetricError(DvcException):
+    def __init__(self, paths):
+        super(BadMetricError, self).__init__(
+            "the following metrics do not exists, "
+            "are not metric files or are malformed: {paths}".format(
+                paths=", ".join("'{}'".format(path) for path in paths)
+            )
+        )
+
+
 class NoMetricsError(DvcException):
     def __init__(self):
         super(NoMetricsError, self).__init__(

dvc/repo/metrics/show.py

@@ -152,12 +152,11 @@ def _read_metric(fd, typ=None, xpath=None, fname=None, branch=None):
         return None
 
 
-def _collect_metrics(repo, targets, recursive, typ, xpath, branch):
+def _collect_metrics(repo, path, recursive, typ, xpath, branch):
     """Gather all the metric outputs.
 
     Args:
-        targets (list): List of paths to metric files or directories.
-            If there's no target, collect all metrics.
+        path (str): Path to a metric file or a directory.
         recursive (bool): If path is a directory, do a recursive search for
             metrics on the given path.
         typ (str): The type that will be used to interpret the metric file,
@@ -172,25 +171,20 @@ def _collect_metrics(repo, targets, recursive, typ, xpath, branch):
             - xpath:
     """
     outs = [out for stage in repo.stages() for out in stage.outs]
-    found = []
 
-    if targets:
-        for target in targets:
-            try:
-                found += repo.find_outs_by_path(
-                    target, outs=outs, recursive=recursive
+    if path:
+        try:
+            outs = repo.find_outs_by_path(path, outs=outs, recursive=recursive)
+        except OutputNotFoundError:
+            logger.debug(
+                "DVC-file not for found for '{}' in branch '{}'".format(
+                    path, branch
                 )
-            except OutputNotFoundError:
-                logger.debug(
-                    "DVC-file not for found for '{}' in branch '{}'".format(
-                        target, branch
-                    )
-                )
-    else:
-        found = outs
+            )
+            return []
 
     res = []
-    for o in found:
+    for o in outs:
         if not o.metric:
             continue
 
@@ -273,16 +267,32 @@ def show(
     recursive=False,
 ):
     res = {}
+    found = set()
+
+    if not targets:
+        # Iterate once to call `_collect_metrics` on all the stages
+        targets = [None]
 
     for branch in repo.brancher(all_branches=all_branches, all_tags=all_tags):
-        entries = _collect_metrics(
-            repo, targets, recursive, typ, xpath, branch
-        )
-        metrics = _read_metrics(repo, entries, branch)
+        metrics = {}
+
+        for p in targets:
+            entries = _collect_metrics(repo, p, recursive, typ, xpath, branch)
+            metric = _read_metrics(repo, entries, branch)
+
+            if metric:
+                found.add(p)
+                metrics.update(metric)
+
         if metrics:
             res[branch] = metrics
 
-    if not res and not targets:
+    if not res and not any(targets):
         raise NoMetricsError()
 
+    missing = set(targets) - found
+
+    if missing:
+        res["_missing"] = missing
+
     return res

tests/func/test_metrics.py

@@ -415,7 +415,7 @@ class TestMetricsRecursive(TestDvcGit):
         ret = self.dvc.metrics.show(
             ["nested"], all_branches=True, recursive=False
         )
-        self.assertEqual(len(ret), 0)
+        self.assertEqual(len(ret), 1)
 
         ret = self.dvc.metrics.show(
             ["nested"], all_branches=True, recursive=True