apply --root: thinkofix.

The end of a string is string[length-1], not string[length+1].
I pointed it out during the review, but I forgot about it when applying the
patch.  This should fix it.

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

builtin-apply.c

@@ -3130,10 +3130,10 @@ int cmd_apply(int argc, const char **argv, const char *unused_prefix)
 			inaccurate_eof = 1;
 			continue;
 		}
-		if (!strncmp(arg, "--root=", strlen("--root="))) {
+		if (!prefixcmp(arg, "--root=")) {
 			arg += strlen("--root=");
 			root_len = strlen(arg);
-			if (root_len && arg[root_len + 1] != '/') {
+			if (root_len && arg[root_len - 1] != '/') {
 				char *new_root;
 				root = new_root = xmalloc(root_len + 2);
 				strcpy(new_root, arg);

t/t4128-apply-root.sh

@@ -8,7 +8,9 @@ test_expect_success 'setup' '
 
 	mkdir -p some/sub/dir &&
 	echo Hello > some/sub/dir/file &&
-	git add some/sub/dir/file
+	git add some/sub/dir/file &&
+	git commit -m initial &&
+	git tag initial
 
 '
 
@@ -21,7 +23,7 @@ diff a/bla/blub/dir/file b/bla/blub/dir/file
 +Bello
 EOF
 
-test_expect_success 'apply --root -p --index' '
+test_expect_success 'apply --root -p (1)' '
 
 	git apply --root=some/sub -p3 --index patch &&
 	test Bello = $(git show :some/sub/dir/file) &&
@@ -29,4 +31,13 @@ test_expect_success 'apply --root -p --index' '
 
 '
 
+test_expect_success 'apply --root -p (2) ' '
+
+	git reset --hard initial &&
+	git apply --root=some/sub/ -p3 --index patch &&
+	test Bello = $(git show :some/sub/dir/file) &&
+	test Bello = $(cat some/sub/dir/file)
+
+'
+
 test_done