apply: strip ./ prefix from --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).

Since using "./" is almost memory muscle for many, strip the "./"
prefix so it behaves the same as --directory=some/sub.

Signed-off-by: Joaquim Rocha <joaquim@amutable.com>

Author: joaquimrocha

apply.c

@@ -5001,6 +5001,10 @@ static int apply_option_parse_directory(const struct option *opt,
 	BUG_ON_OPT_NEG(unset);
 
 	strbuf_reset(&state->root);
+
+	if (starts_with(arg, "./"))
+		arg += 2;
+
 	strbuf_addstr(&state->root, arg);
 	strbuf_complete(&state->root, '/');
 	return 0;

t/t4128-apply-root.sh

@@ -43,6 +43,15 @@ 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
+'
+
 cat > patch << EOF
 diff --git a/newfile b/newfile
 new file mode 100644