file helper did not preserve relative paths

framework/helpers/BaseFileHelper.php

@@ -48,7 +48,7 @@ class BaseFileHelper
         // the path may contain ".", ".." or double slashes, need to clean them up
         $parts = [];
         foreach (explode($ds, $path) as $part) {
-            if ($part === '..' && !empty($parts)) {
+            if ($part === '..' && !empty($parts) && end($parts) !== '..') {
                 array_pop($parts);
             } elseif ($part === '.' || $part === '' && !empty($parts)) {
                 continue;

tests/unit/framework/helpers/FileHelperTest.php

@@ -367,6 +367,14 @@ class FileHelperTest extends TestCase
         $this->assertEquals("{$ds}c", FileHelper::normalizePath('/a/.\\b//../../c'));
         $this->assertEquals("c", FileHelper::normalizePath('/a/.\\b/../..//../c'));
         $this->assertEquals("..{$ds}c", FileHelper::normalizePath('//a/.\\b//..//..//../../c'));
+
+        // relative paths
+        $this->assertEquals("..{$ds}..{$ds}a", FileHelper::normalizePath('../..\\a'));
+        $this->assertEquals("..{$ds}..{$ds}a", FileHelper::normalizePath('../..\\a/../a'));
+        $this->assertEquals("..{$ds}..{$ds}b", FileHelper::normalizePath('../..\\a/../b'));
+        $this->assertEquals("..{$ds}a", FileHelper::normalizePath('./..\\a'));
+        $this->assertEquals("..{$ds}a", FileHelper::normalizePath('./..\\a/../a'));
+        $this->assertEquals("..{$ds}b", FileHelper::normalizePath('./..\\a/../b'));
     }
 
     public function testLocalizedDirectory()