diff: correct interaction between --exit-code and -I<pattern>

Just like "git diff -w --exit-code" should exit with 0 when ignoring
whitespace differences results in no changes shown, if ignoring
certain changes with "git diff -I<pattern> --exit-code" result in an
empty patch, we should exit with 0.

The test suite did not cover the interaction between "--exit-code"
and "-w"; add one while adding a new test for "--exit-code" + "-I".

Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/diff.c b/diff.c
index 92e247fb83..e162d59eae 100644
--- a/diff.c
+++ b/diff.c
@@ -4602,7 +4602,8 @@ void diff_setup_done(struct diff_options *options)
 	 * inside contents.
 	 */
 
-	if ((options->xdl_opts & XDF_WHITESPACE_FLAGS))
+	if ((options->xdl_opts & XDF_WHITESPACE_FLAGS) ||
+	    options->ignore_regex_nr)
 		options->flags.diff_from_contents = 1;
 	else
 		options->flags.diff_from_contents = 0;