brancher refactor

dvc/repo/brancher.py

@@ -36,9 +36,9 @@ def brancher(  # noqa: E302
     if all_tags:
         tags = scm.list_tags()
 
-    if branches is None:
+    if branches is None and not (all_tags and not all_branches):
         revs.extend([scm.active_branch()])
-    else:
+    elif branches is not None:
         revs.extend(branches)
 
     if tags is not None:

dvc/repo/metrics/show.py

@@ -269,9 +269,6 @@ def show(
         if metrics:
             res[branch] = metrics
 
-    if all_tags and not all_branches:
-        res.pop(repo.scm.active_branch())
-
     if not res:
         if path:
             raise BadMetricError(path)