diff: the -w option breaks --exit-code for --raw and other output modes

The output from "--raw", "--name-status", and "--name-only" modes in
"git diff" does depend on and does not reflect how certain different
contents are considered equal, unlike "--patch" and "--stat" output
modes do, when used with options like "-w" (another way of thinking
about it is that it is not like we recompute the hash of the blob
after removing all whitespaces to show "git diff --raw -w" output).

But the fact that "--raw" and friends ignore "-w" is not a good
excuse for "diff --raw -w --exit-code" to also ignore the request to
report the differences with its exit status.  When run without "-w",
"git diff --exit-code --raw" does report with its exit status the
differences as requested, and we should do the same when run with
"-w", too.

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

diff.c

@@ -4744,6 +4744,10 @@ void diff_setup_done(struct diff_options *options)
 	else
 		options->prefix_length = 0;
 
+	/*
+	 * --name-only, --name-status, --checkdiff, and -s
+	 * turn other output format off.
+	 */
 	if (options->output_format & (DIFF_FORMAT_NAME |
 				      DIFF_FORMAT_NAME_STATUS |
 				      DIFF_FORMAT_CHECKDIFF |
@@ -6072,6 +6076,8 @@ static void flush_one_pair(struct diff_filepair *p, struct diff_options *opt)
 		fprintf(opt->file, "%s", diff_line_prefix(opt));
 		write_name_quoted(name_a, opt->file, opt->line_termination);
 	}
+
+	opt->found_changes = 1;
 }
 
 static void show_file_mode_name(struct diff_options *opt, const char *newdelete, struct diff_filespec *fs)

t/t4015-diff-whitespace.sh

@@ -11,8 +11,12 @@ TEST_PASSES_SANITIZE_LEAK=true
 . ./test-lib.sh
 . "$TEST_DIRECTORY"/lib-diff.sh
 
-for opts in --patch --quiet -s --stat --shortstat --dirstat=lines
+for opt_res in --patch --quiet -s --stat --shortstat --dirstat=lines \
+	       --raw! --name-only! --name-status!
 do
+	opts=${opt_res%!} expect_failure=
+	test "$opts" = "$opt_res" ||
+		expect_failure="test_expect_code 1"
 
 	test_expect_success "status with $opts (different)" '
 		echo foo >x &&
@@ -40,7 +44,7 @@ do
 		echo foo >x &&
 		git add x &&
 		echo " foo" >x &&
-		git diff -w $opts --exit-code x
+		$expect_failure git diff -w $opts --exit-code x
 	'
 done