Fix ensureDirectoryExists not working when a broken symlink appears somewhere in the path, fixes #11864

src/Composer/Util/Filesystem.php

@@ -257,7 +257,21 @@ class Filesystem
             }
 
             if (!@mkdir($directory, 0777, true)) {
-                throw new \RuntimeException($directory.' does not exist and could not be created: '.(error_get_last()['message'] ?? ''));
+                $e = new \RuntimeException($directory.' does not exist and could not be created: '.(error_get_last()['message'] ?? ''));
+
+                // in pathological cases with paths like path/to/broken-symlink/../foo is_dir will fail to detect path/to/foo
+                // but normalizing the ../ away first makes it work so we attempt this just in case, and if it still fails we
+                // report the initial error we had with the original path, and ignore the normalized path exception
+                // see https://github.com/composer/composer/issues/11864
+                $normalized = $this->normalizePath($directory);
+                if ($normalized !== $directory) {
+                    try {
+                        $this->ensureDirectoryExists($normalized);
+                        return;
+                    } catch (\Throwable $ignoredEx) {}
+                }
+
+                throw $e;
             }
         }
     }