src/Composer/Util/Filesystem.php
public function isSymlinkedDirectory($directory)
    {
        if (!is_dir($directory)) {
            return false;
        }

        $resolved = $this->resolveSymlinkedDirectorySymlink($directory);

        return is_link($resolved);
    }
public function isSymlinkedDirectory($directory)
    {
        if (!is_dir($directory)) {
            return false;
        }

        $resolved = $this->resolveSymlinkedDirectorySymlink($directory);

        return is_link($resolved);
    }
return true if that directory is a symlink.

@param string $directory

@return bool