Add support for Laravel 9

[tabacitu]

WHY

BEFORE - What was wrong? What was happening before this PR?

Could not install Backpack on Laravel 9.

AFTER - What is happening after this PR?

Can install, but only Backpack 4.2. I think this is a good way to proceed, because if you have the time to upgrade Laravel, you should also have the time to upgrade Backpack.

HOW

How did you achieve that, in technical terms?

Bumped composer.json requirements.

Is it a breaking change or non-breaking change?

Non-breaking for 4.2.

How can we test the before & after?

Try installing without - shouldn't work. Try installing with - should work.

[tabacitu]

While adding support, I've discovered quite a few issues in our dependencies. These ALL need to be fixed, in order to be able to provide full support for Laravel 9:

MUST-DOs, otherwise we can't say we provide support:

• exception on all pages, because prologue/alerts AlertsMessageBag::count() declaration must be compatible with Illuminate\Support\MessageBag::count() in v9; fixed by add support for Laravel 9, remove support for everything else prologuephp/alerts#39
• error on @php artisan package:discover because fideloper/proxy has not tagged a new version in 1.5 years (workaround - use dev-master as 4.4.99); solved by removing the fideloper/proxy dependency entirely, since the demo doesn't actually use it;

SHOULD-DOs, otherwise some Backpack addons won't work under Laravel 9:

• conflict because of DevTools, which requires Livewire, which requires symfony/http-kernel v5 (will probably be solved in Laravel 9 support livewire/livewire#4544);
• conflict because of BackupManager, which requires spatie/backups v6 and does not support v8 yet; fixed by add support for spatie v7 and v8 and backpack 4.2 BackupManager#98
• confict because of FileManager, which requires barryvdh/laravel-elfinder, which requires flysystem v1 (OUCH!);

[tabacitu]

Turns out Backpack/CRUD doesn't really need much to support Laravel 9. So I'm going to merge this into 4.2, so we can also test against it. We still need to add support to two of our dependencies in order to "fully" support L9, though. But I've mentioned that in Laravel-Backpack/demo#342 which will stay open until we do (could take a few days).

[lakuapik]

@tabacitu will this laravel 9 support lands on 4.x eventually or its only available for 5.x ?

[tabacitu]

Hi @lakuapik ,

We don't plan on adding L9 support to Backpack 4.1 - it supports already L6, L7 and L8.

If we added L9 support to B4.1 it would mean people would be using it B4.1 for 1+ year going forward, which would mean bug reports and feature requests 1+ year going forwards. Unfortunately we don't have that kind of resources, we can only focus on one major version at a time - and right now that version is 5.x. We'll still add a few minor fixes we want in 4.1, and security fixes if they are ever needed... but we can't maintain it any longer, I'm afraid, so L9 support is a no-go.

Plus, v5 is a super-easy upgrade for most people, there's no reason not to upgrade.

Cheers!