Merge branch 'jk/rev-list-empty-input' into maint

"git log --tag=no-such-tag" showed log starting from HEAD, which
has been fixed---it now shows nothing.

* jk/rev-list-empty-input:
  revision: do not fallback to default when rev_input_given is set
  rev-list: don't show usage when we see empty ref patterns
  revision: add rev_input_given flag
  t6018: flesh out empty input/output rev-list tests

builtin/rev-list.c

@@ -352,7 +352,8 @@ int cmd_rev_list(int argc, const char **argv, const char *prefix)
 
 	if ((!revs.commits && reflog_walk_empty(revs.reflog_info) &&
 	     (!(revs.tag_objects || revs.tree_objects || revs.blob_objects) &&
-	      !revs.pending.nr)) ||
+	      !revs.pending.nr) &&
+	     !revs.rev_input_given) ||
 	    revs.diff)
 		usage(rev_list_usage);