rev-list: don't show usage when we see empty ref patterns

If the user gives us no starting point for a traversal, we
want to complain with our normal usage message. But if they
tried to do so with "--all" or "--glob", but that happened
not to match any refs, the usage message isn't helpful. We
should just give them the empty output they asked for
instead.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/rev-list.c

diff --git a/builtin/rev-list.c b/builtin/rev-list.c
index 95d84d5..1e9cc59 100644
--- a/builtin/rev-list.c
+++ b/builtin/rev-list.c
@@ -350,7 +350,8 @@ int cmd_rev_list(int argc, const char **argv, const char *prefix)
 
 	if ((!revs.commits &&
 	     (!(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);
 

t/t6018-rev-list-glob.sh

diff --git a/t/t6018-rev-list-glob.sh b/t/t6018-rev-list-glob.sh
index f8367b8..d3453c5 100755
--- a/t/t6018-rev-list-glob.sh
+++ b/t/t6018-rev-list-glob.sh
@@ -261,13 +261,13 @@
 	test_cmp expect actual
 '
 
-test_expect_failure 'rev-list should succeed with empty output with all refs excluded' '
+test_expect_success 'rev-list should succeed with empty output with all refs excluded' '
 	>expect &&
 	git rev-list --exclude=* --all >actual &&
 	test_cmp expect actual
 '
 
-test_expect_failure 'rev-list should succeed with empty output with empty --all' '
+test_expect_success 'rev-list should succeed with empty output with empty --all' '
 	(
 		test_create_repo empty &&
 		cd empty &&
@@ -277,7 +277,7 @@
 	)
 '
 
-test_expect_failure 'rev-list should succeed with empty output with empty glob' '
+test_expect_success 'rev-list should succeed with empty output with empty glob' '
 	>expect &&
 	git rev-list --glob=does-not-match-anything >actual &&
 	test_cmp expect actual