apply: normalize path in --directory argument

When passing a relative path like --directory=./some/sub, the leading
"./" caused apply to prepend it literally to patch filenames, resulting
in an error (invalid path).
There may be more cases like this where users pass some/./path to the
directory which can easily be normalized to an acceptable path, so
these changes try to normalize the path before using it.

Signed-off-by: Joaquim Rocha <joaquim@amutable.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: joaquimrocha

apply.c

@@ -4963,6 +4963,10 @@ static int apply_option_parse_directory(const struct option *opt,
 
 	strbuf_reset(&state->root);
 	strbuf_addstr(&state->root, arg);
+
+	if (strbuf_normalize_path(&state->root) < 0)
+		return error(_("unable to normalize directory: '%s'"), arg);
+
 	strbuf_complete(&state->root, '/');
 	return 0;
 }

t/t4128-apply-root.sh

@@ -43,6 +43,47 @@ test_expect_success 'apply --directory -p (2) ' '
 
 '
 
+test_expect_success 'apply --directory (./ prefix)' '
+	git reset --hard initial &&
+	git apply --directory=./some/sub -p3 --index patch &&
+	echo Bello >expect &&
+	git show :some/sub/dir/file >actual &&
+	test_cmp expect actual &&
+	test_cmp expect some/sub/dir/file
+'
+
+test_expect_success 'apply --directory (double slash)' '
+	git reset --hard initial &&
+	git apply --directory=some//sub -p3 --index patch &&
+	echo Bello >expect &&
+	git show :some/sub/dir/file >actual &&
+	test_cmp expect actual &&
+	test_cmp expect some/sub/dir/file
+'
+
+test_expect_success 'apply --directory (./ in the middle)' '
+	git reset --hard initial &&
+	git apply --directory=some/./sub -p3 --index patch &&
+	echo Bello >expect &&
+	git show :some/sub/dir/file >actual &&
+	test_cmp expect actual &&
+	test_cmp expect some/sub/dir/file
+'
+
+test_expect_success 'apply --directory (../ in the middle)' '
+	git reset --hard initial &&
+	git apply --directory=some/../some/sub -p3 --index patch &&
+	echo Bello >expect &&
+	git show :some/sub/dir/file >actual &&
+	test_cmp expect actual &&
+	test_cmp expect some/sub/dir/file
+'
+
+test_expect_success 'apply --directory rejects leading ../' '
+	test_must_fail git apply --directory=../foo -p3 patch 2>err &&
+	test_grep "unable to normalize directory" err
+'
+
 cat > patch << EOF
 diff --git a/newfile b/newfile
 new file mode 100644