[PATCH] Show error for 'git merge' with unset merge.defaultToUpstream

[Vincent van Ravesteijn <vfr@lyx.org>]

'git merge' can be called without any arguments if merge.defaultToUpstream
is set. However, when merge.defaultToUpstream is not set, the user will be
presented the usage information as if he entered a command with a wrong
syntaxis. Ironically, the usage information confirms that no arguments are
mandatory.

This adds a proper error message telling the user why the command failed. As
a side-effect this can help the user in discovering the possibility to merge
with the upstream branch by setting merge.defaultToUpstream.

Signed-off-by: Vincent van Ravesteijn <vfr@lyx.org>
---
 builtin/merge.c |    9 ++++++---
 1 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/builtin/merge.c b/builtin/merge.c
index dffd5ec..900a297 100644
--- a/builtin/merge.c
+++ b/builtin/merge.c
@@ -1160,9 +1160,12 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
 		die(_("You cannot combine --no-ff with --ff-only."));
 
 	if (!abort_current_merge) {
-		if (!argc && default_to_upstream)
-			argc = setup_with_upstream(&argv);
-		else if (argc == 1 && !strcmp(argv[0], "-"))
+		if (!argc) {
+			if (default_to_upstream)
+				argc = setup_with_upstream(&argv);
+			else
+				die(_("No commit specified and merge.defaultToUpstream not set."));
+		} else if (argc == 1 && !strcmp(argv[0], "-"))
 			argv[0] = "@{-1}";
 	}
 	if (!argc)
-- 
1.7.4.1