[7.x] Fix null value injected from container in routes

[mathieutu]

Hi,

This PR fixes laravel/ideas#2114 (no idea why this bug have been moved to ideas, maybe I haven't made me understood 😕)

Context:
When injecting something witch can be null, the \Illuminate\Routing\RouteDependencyResolverTrait::resolveMethodDependencies method doesn't add it to parameters to inject, because it can't difference it from void return.

I've added a default return value, to indicate that we want to strip the value, to allow null value.

• This PR should not be a breaking change: all tests pass, and the previous behavior was not changed.
• A test to address this case was added.

You can reproduce the bug with:

class AppServiceProvider extends ServiceProvider
{
    public function register()
    {
        $this->app->bind(Service::class, fn() => null);
    }

    public function boot()
    {
        Route::get('/foo/{id}', function (?Service $service, string $id) {
            // Argument 1 passed ... must be an instance of Service or null, string given.
        });

        Route::get('/not-working', function (?Service $service) {
            // Too few arguments ... 0 passed ... and exactly 1 expected.
        });

        Route::get('/working', function (?Service $service = null) {
            // Working
        });
    }
}

And see the errors thrown:

• https://flareapp.io/share/bP9OdL5Q
• https://flareapp.io/share/omwgpomE

Thanks.

Matt'

PS: If you read this, and can answer to this https://twitter.com/mathieutu/status/1236997027122249728?s=20, I would like to propose a PR for the router with a quite important breaking change, and so understand why the behavior of Laravel routing is like that, and why it is different from standard one.
Thanks.

[mathieutu]

StyleCI's not happy, but I'm not comfortable with the change proposed, as it makes the function not understandable.

-        $container->bind(RoutingTestUserModel::class, function() {
-            return null;
+        $container->bind(RoutingTestUserModel::class, function () {
         });

[GrahamCampbell]

Laravel's code standard is like this because when a fucntion that has no return statement is called and the result is used or assigned to a variable, it is the same as using the value null in its place. The actual return statement can be optimized away.

[deleugpn]

I actually tried to fix this about 2 weeks ago and my patch was so bad that I never sent it. This looks like a really good patch with minor code changes to fix a moderate problem.
As someone who failed to find a good solution for this, I can appreciate the nice job you did there.

[mpyw]

Related:

• [5.6] Allow nullable method injection by mpyw · Pull Request #22488 · laravel/framework