diff: allow --no-patch as synonym for -s

This follows the usual convention of having a --no-foo option to negate
--foo.

Signed-off-by: Matthieu Moy <Matthieu.Moy@imag.fr>
Reviewed-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/rev-list-options.txt

@@ -839,5 +839,6 @@ options may be given. See linkgit:git-diff-files[1] for more options.
 	Show the tree objects in the diff output. This implies '-r'.
 
 -s::
+--no-patch::
 	Suppress diff output.
 endif::git-rev-list[]

diff.c

@@ -3540,7 +3540,7 @@ int diff_opt_parse(struct diff_options *options, const char **av, int ac)
 		options->output_format |= DIFF_FORMAT_NAME;
 	else if (!strcmp(arg, "--name-status"))
 		options->output_format |= DIFF_FORMAT_NAME_STATUS;
-	else if (!strcmp(arg, "-s"))
+	else if (!strcmp(arg, "-s") || !strcmp(arg, "--no-patch"))
 		options->output_format |= DIFF_FORMAT_NO_OUTPUT;
 	else if (!prefixcmp(arg, "--stat"))
 		/* --stat, --stat-width, --stat-name-width, or --stat-count */

t/t4000-diff-format.sh

@@ -59,4 +59,16 @@ test_expect_success 'validate git diff-files -p output.' '
 	compare_diff_patch expected actual
 '
 
+test_expect_success 'git diff-files -s after editing work tree' '
+	git diff-files -s >actual 2>err &&
+	test_must_be_empty actual &&
+	test_must_be_empty err
+'
+
+test_expect_success 'git diff-files --no-patch as synonym for -s' '
+	git diff-files --no-patch >actual 2>err &&
+	test_must_be_empty actual &&
+	test_must_be_empty err
+'
+
 test_done