Actually adding the file

src/ORM/AssociationsNormalizerTrait.php

@@ -0,0 +1,66 @@
+<?php
+/**
+ * CakePHP(tm) : Rapid Development Framework (http://cakephp.org)
+ * Copyright (c) Cake Software Foundation, Inc. (http://cakefoundation.org)
+ *
+ * Licensed under The MIT License
+ * For full copyright and license information, please see the LICENSE.txt
+ * Redistributions of files must retain the above copyright notice.
+ *
+ * @copyright     Copyright (c) Cake Software Foundation, Inc. (http://cakefoundation.org)
+ * @link          http://cakephp.org CakePHP(tm) Project
+ * @since         3.0.0
+ * @license       http://www.opensource.org/licenses/mit-license.php MIT License
+ */
+namespace Cake\ORM;
+
+/**
+ * Contains methods for parsing the associated tables array that is typically
+ * passed to  a save operation
+ */
+trait AssociationsNormalizerTrait {
+
+/**
+ * Returns an array out of the original passed associations list where dot notation
+ * is transformed into nested arrays so that they can be parsed by other routines
+ *
+ * @param array $associations The array of included associations.
+ * @return array An array having dot notation trnasformed into nested arrays
+ */
+	protected function _normalizeAssociations($associations) {
+		$result = [];
+		foreach ($associations as $table => $options) {
+			$pointer =& $result;
+
+			if (is_int($table)) {
+				$table = $options;
+				$options = [];
+			}
+
+			if (!strpos($table, '.')) {
+				$result[$table] = $options;
+				continue;
+			}
+
+			$path = explode('.', $table);
+			$table = array_pop($path);
+			$first = array_shift($path);
+			$pointer += [$first => []];
+			$pointer =& $pointer[$first];
+			$pointer += ['associated' => []];
+
+			foreach ($path as $t) {
+				$pointer += ['associated' => []];
+				$pointer['associated'] += [$t => []];
+				$pointer['associated'][$t] += ['associated' => []];
+				$pointer =& $pointer['associated'][$t];
+			}
+
+			$pointer['associated'] += [$table => []];
+			$pointer['associated'][$table] = $options + $pointer['associated'][$table];
+		}
+
+		return isset($result['associated']) ? $result['associated'] : $result;
+	}
+
+}