valid Mai ACF fields

For #651

lib/fields/validate.php

@@ -0,0 +1,35 @@
+<?php
+/**
+ * Mai Engine.
+ *
+ * @package   BizBudding\MaiEngine
+ * @link      https://bizbudding.com
+ * @author    BizBudding
+ * @copyright Copyright © 2020 BizBudding
+ * @license   GPL-2.0-or-later
+ */
+
+// Prevent direct file access.
+defined( 'ABSPATH' ) || die;
+
+add_filter( 'acf/is_field_key', 'mai_acf_is_field_key', 10, 2 );
+/**
+ * Checks if a field key is a valid ACF field key.
+ * We need this because we wrongly used custom field keys that don't start with `field_`.
+ * Our engine blocks use `mai_` and plugin blocks use `maicca_', `maipub_`, etc., so we check for `mai`.
+ *
+ * @since TBD
+ *
+ * @param bool   $bool The result.
+ * @param string $id   The identifier.
+ *
+ * @return bool
+ */
+function mai_acf_is_field_key( $bool, $id ) {
+	// Bail if already true.
+	if ( $bool ) {
+		return $bool;
+	}
+
+	return $id && str_starts_with( $id, 'mai' );
+}

lib/init.php

@@ -361,6 +361,7 @@ function mai_load_files() {
 		'fields/icons',
 		'fields/wp-query',
 		'fields/wp-term-query',
+		'fields/validate',
 
 		// Blocks.
 		'blocks/general',