diff: allow --color-moved with --no-ext-diff

We ignore the option --color-moved if an external diff program is
configured, presumably because its overhead is unnecessary in that case.
Respect the option if we don't actually use the external diff, though.

Reported-by: lolligerhans@gmx.de
Helped-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: rscharfe

diff.c

@@ -4926,7 +4926,8 @@ void diff_setup_done(struct diff_options *options)
 	if (options->flags.follow_renames)
 		diff_check_follow_pathspec(&options->pathspec, 1);
 
-	if (!options->use_color || external_diff())
+	if (!options->use_color ||
+	    (options->flags.allow_external && external_diff()))
 		options->color_moved = 0;
 
 	if (options->filter_not) {

t/t4015-diff-whitespace.sh

@@ -1184,6 +1184,15 @@ test_expect_success 'detect moved code, complete file' '
 	test_cmp expected actual
 '
 
+test_expect_success '--color-moved with --no-ext-diff' '
+	test_config color.diff.oldMoved "yellow" &&
+	test_config color.diff.newMoved "blue" &&
+	args="--color --color-moved=zebra --no-renames HEAD" &&
+	git diff $args >expect &&
+	git -c diff.external=echo diff --no-ext-diff $args >actual &&
+	test_cmp expect actual
+'
+
 test_expect_success 'detect malicious moved code, inside file' '
 	test_config color.diff.oldMoved "normal red" &&
 	test_config color.diff.newMoved "normal green" &&