bug #11726 [Filesystem Component] mkdir race condition fix #11626 (kc…

…assam)

This PR was squashed before being merged into the 2.3 branch (closes #11726).

Discussion
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[Filesystem Component] mkdir race condition fix #11626

[Filesystem Component] Fix mkdir race condition

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #11626
| License       | MIT
| Doc PR        | none

Commits
-------

0483452 [Filesystem Component] mkdir race condition fix #11626

src/Symfony/Component/Filesystem/Filesystem.php

@@ -78,7 +78,14 @@ public function mkdir($dirs, $mode = 0777)
             }
 
             if (true !== @mkdir($dir, $mode, true)) {
-                throw new IOException(sprintf('Failed to create %s', $dir));
+                $error = error_get_last();
+                if (!is_dir($dir)) {
+                    // The directory was not created by a concurrent process. Let's throw an exception with a developer friendly error message if we have one
+                    if ($error) {
+                        throw new IOException(sprintf('Failed to create "%s": %s.', $dir, $error['message']));
+                    }
+                    throw new IOException(sprintf('Failed to create "%s"', $dir));
+                }
             }
         }
     }