Flarum Custom Layout Extension

bootstrap.php

<?php

namespace Flarum\CustomLayout;

use Flarum\Support\Extension as BaseExtension;
use Illuminate\Events\Dispatcher;
use Flarum\Events\BuildClientView;
use Flarum\Forum\Actions\ClientAction as ForumClientAction;

class Extension extends BaseExtension
{
    public function listen(Dispatcher $events)
    {
        $events->listen(BuildClientView::class, function (BuildClientView $event) {
            if ($event->action instanceof ForumClientAction) {
                $event->view->setLayout(__DIR__.'/forum.blade.php');
            }
        });
    }
}

return Extension::class;

use Illuminate\Events\Dispatcher;
use Flarum\Event\ConfigureClientView;

return function( Dispatcher $events ) {
    $events->listen( ConfigureClientView::class, function( ConfigureClientView $event ) {
        $template = 'forum.blade.php';
        $stringLength = strlen( $template );
        if( substr( $event->view->layout, -$stringLength ) === $template ) {
            $event->view->layout = __DIR__.'/forum.blade.php';
        }
    });
};