Using helper function in config file break artisan.

I was having this issue https://laracasts.com/discuss/channels/laravel/2016-php-artisan-dont-show-anything where my artisan command don't work and doesn't show any error. Nor it show anything in the log file.

I am newbie so I created new project and try artisan and it was working in new project. I start copying file from older project into new project and artisan stop working again. I made another project and start copy file/folder one by one. And I found that the cause was of a custom config file i created in config folder. My code looks like this. When i remove url() function , my artisan start to work again.

Although this config file and its value work all across the site. But it just break the artisan command. I don't know why.

My question is it a well known and strict rule that helper function are not allowed in custom config file ?

return [ 'cache_enabled' => false, 'sidebar_menu' => array( array("title" => "Home" , "url" => url('/') ), array("title" => "Contact Us" , "url" => url('/page/contact-us.html')), ) ];