bug symfony#17615 Ensure backend slashes for symlinks on Windows systems (cpsitgmbh)

This PR was submitted for the master branch but it was merged into the 2.3 branch instead (closes symfony#17615).

Discussion
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Ensure backend slashes for symlinks on Windows systems

Resolves: symfony#17614

Commits
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d897956 Ensure backend slashes for symlinks on Windows systems

Author: nicolas-grekas

src/Symfony/Component/Filesystem/Filesystem.php

@@ -301,10 +301,15 @@ private function isReadable($filename)
      */
     public function symlink($originDir, $targetDir, $copyOnWindows = false)
     {
-        if ($copyOnWindows && !function_exists('symlink')) {
-            $this->mirror($originDir, $targetDir);
+        if ('\\' === DIRECTORY_SEPARATOR) {
+            $originDir = strtr($originDir, '/', '\\');
+            $targetDir = strtr($targetDir, '/', '\\');
+
+            if ($copyOnWindows) {
+                $this->mirror($originDir, $targetDir);
 
-            return;
+                return;
+            }
         }
 
         $this->mkdir(dirname($targetDir));