difftool: honor --trust-exit-code for builtin tools

run_merge_tool() was not setting $status, which prevented the
exit code for builtin tools from being forwarded to the caller.

Capture the exit status and add a test to guarantee the behavior.

Reported-by: Adria Farres <14farresa@gmail.com>
Signed-off-by: David Aguilar <davvid@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/git-mergetool--lib.sh b/git-mergetool--lib.sh
index c45a020301..cce4f8c494 100644
--- a/git-mergetool--lib.sh
+++ b/git-mergetool--lib.sh
@@ -221,6 +221,7 @@ run_merge_tool () {
 	else
 		run_diff_cmd "$1"
 	fi
+	status=$?
 	return $status
 }