Merge branch 'ld/maint-diff-quiet-w' into maint

* ld/maint-diff-quiet-w:
  git-diff: add a test for git diff --quiet -w
  git diff --quiet -w: check and report the status

Author: gitster

diff.c

@@ -3522,6 +3522,29 @@ void diff_flush(struct diff_options *options)
 		separator++;
 	}
 
+	if (output_format & DIFF_FORMAT_NO_OUTPUT &&
+	    DIFF_OPT_TST(options, EXIT_WITH_STATUS) &&
+	    DIFF_OPT_TST(options, DIFF_FROM_CONTENTS)) {
+		/*
+		 * run diff_flush_patch for the exit status. setting
+		 * options->file to /dev/null should be safe, becaue we
+		 * aren't supposed to produce any output anyway.
+		 */
+		if (options->close_file)
+			fclose(options->file);
+		options->file = fopen("/dev/null", "w");
+		if (!options->file)
+			die_errno("Could not open /dev/null");
+		options->close_file = 1;
+		for (i = 0; i < q->nr; i++) {
+			struct diff_filepair *p = q->queue[i];
+			if (check_pair_status(p))
+				diff_flush_patch(p, options);
+			if (options->found_changes)
+				break;
+		}
+	}
+
 	if (output_format & DIFF_FORMAT_PATCH) {
 		if (separator) {
 			putc(options->line_termination, options->file);

t/t4017-diff-retval.sh

@@ -5,6 +5,9 @@ test_description='Return value of diffs'
 . ./test-lib.sh
 
 test_expect_success 'setup' '
+	echo "1 " >a &&
+	git add . &&
+	git commit -m zeroth &&
 	echo 1 >a &&
 	git add . &&
 	git commit -m first &&
@@ -13,6 +16,18 @@ test_expect_success 'setup' '
 	git commit -a -m second
 '
 
+test_expect_success 'git diff --quiet -w  HEAD^^ HEAD^' '
+	git diff --quiet -w HEAD^^ HEAD^
+'
+
+test_expect_success 'git diff --quiet HEAD^^ HEAD^' '
+	test_must_fail git diff --quiet HEAD^^ HEAD^
+'
+
+test_expect_success 'git diff --quiet -w  HEAD^ HEAD' '
+	test_must_fail git diff --quiet -w HEAD^ HEAD
+'
+
 test_expect_success 'git diff-tree HEAD^ HEAD' '
 	git diff-tree --exit-code HEAD^ HEAD
 	test $? = 1