revision.c: explain what tree_difference does

diff --git a/builtin-shortlog.c b/builtin-shortlog.c
index 2d7726e8b975d9977e14638cc127ed0b30d3058b..29343aefc843c4dd22095f559262bc6b5e381440 100644 (file)
--- a/builtin-shortlog.c
+++ b/builtin-shortlog.c
@@ -304,8 +304,11 @@ int cmd_shortlog(int argc, const char **argv, const char *prefix)
        if (!access(".mailmap", R_OK))
                read_mailmap(".mailmap");
 
-       if (rev.pending.nr == 0)
+       if (rev.pending.nr == 0) {
+               if (isatty(0))
+                       fprintf(stderr, "(reading log to summarize from standard input)\n");
                read_from_stdin(&list);
+       }
        else
                get_from_rev(&rev, &list);