…ices (nicolas-grekas)

This PR was merged into the 3.3-dev branch.

Discussion
----------

[DI] Allow extensions to create ServiceLocator as services

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

https://github.com/symfony/symfony/pull/21770/files?w=1

With this PR, DI extensions are able to create "service locator" services.
They are easily created as such:
```php
$container->register('my_service_locator', ServiceLocator::class)
    ->addArgument(array(
        'exposed_id' => new ServiceClosureArgument(new Reference('internal_id')),
    ))
```
I already need this in two different PRs to come.

Commits
-------

1d96633 [DI] Allow creating ServiceLocator-based services in extensions

…s" tag to inject services into actions (nicolas-grekas)

This PR was merged into the 3.3-dev branch.

Discussion
----------

[FrameworkBundle] Add new "controller.service_arguments" tag to inject services into actions

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | (no test yet)
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

Talking with @simensen and @weaverryan, we wondered if we could leverage the `ArgumentResolver` mechanism to make it inject services on demand, using e.g. autowiring.

```php
class PostController
{
  public function indexAction(Request $request, PostRepository $postRepository)
  {
    // PostRepository comes from the container
    $postRepository->findAll(); // ...
  }
}
```

This PR achieves that, using a new "controller.service_arguments" tag. Typically:
```yaml
services:
    AppBundle\Controller\PostController:
        autowire: true
        tags:
            - name: controller.service_arguments
```

It also supports with explicit wiring (thus doesn't necessarily require autowiring if you don't want to use it):
```yaml
services:
    AppBundle\Controller\PostController:
        tags:
            - name: controller.service_arguments
              action: fooAction
              argument: logger
              id: my_logger
```

~~The attached diff is bigger than strictly required for now, until #21770 is merged.~~

Todo:
- [x] rebase on top of #21770 when merged
- [x] add tests
- [x] add cleaning pass to remove empty service locators

Commits
-------

9c6e672 [FrameworkBundle] Add new "controller.service_arguments" tag to inject services into actions

…es (HypeMC)

This PR was merged into the 5.4 branch.

Discussion
----------

[DependencyInjection] Add section about Service Closures

Documents service closures added in symfony/symfony#21770 and symfony/symfony#41176, and the `service_closure()` PHP-DSL function added in symfony/symfony#42625 .

Commits
-------

f2b2fdb [DI] Add section about Service Closures