Merge branch 'jk/diff-from-contents-fix' into maint-2.51

Recently we attempted to improve "git diff -w" and friends to
handle cases where patch output would be suppressed, but it
introduced a bug that emits unnecessary output, which has been
corrected.

* jk/diff-from-contents-fix:
  diff: restore redirection to /dev/null for diff_from_contents

Author: gitster

diff.c

@@ -6876,6 +6876,15 @@ void diff_flush(struct diff_options *options)
 	if (output_format & DIFF_FORMAT_NO_OUTPUT &&
 	    options->flags.exit_with_status &&
 	    options->flags.diff_from_contents) {
+		/*
+		 * run diff_flush_patch for the exit status. setting
+		 * options->file to /dev/null should be safe, because we
+		 * aren't supposed to produce any output anyway.
+		 */
+		diff_free_file(options);
+		options->file = xfopen("/dev/null", "w");
+		options->close_file = 1;
+		options->color_moved = 0;
 		for (i = 0; i < q->nr; i++) {
 			struct diff_filepair *p = q->queue[i];
 			if (check_pair_status(p))

t/t4035-diff-quiet.sh

@@ -50,6 +50,10 @@ test_expect_success 'git diff-tree HEAD HEAD' '
 	test_expect_code 0 git diff-tree --quiet HEAD HEAD >cnt &&
 	test_line_count = 0 cnt
 '
+test_expect_success 'git diff-tree -w HEAD^ HEAD' '
+	test_expect_code 1 git diff-tree --quiet -w HEAD^ HEAD >cnt &&
+	test_line_count = 0 cnt
+'
 test_expect_success 'git diff-files' '
 	test_expect_code 0 git diff-files --quiet >cnt &&
 	test_line_count = 0 cnt