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

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

@@ -261,13 +261,13 @@ test_expect_failure 'rev-list should succeed with empty output on empty stdin' '
 	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 --all'
 	)
 '
 
-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