[DependencyInjection] Ambiguous wording regarding `_defaults` in `services.yaml`; using `when@<env>` does not use `_defaults`

[ToshY]

Problem

The documentation regarding the autoconfigure option states the following regarding _defaults:

Above, the services.yaml file has autoconfigure: true in the _defaults section so that it applies to all services defined in that file. With this setting, the container will automatically apply certain configuration to your services, based on your service's class. This is mostly used to auto-tag your services.

(this is also denoted in symfony/symfony#28326 (comment) that the defaults are file-based)

With the introduction of using when@<env> tags that can be used within the same file, like services.yaml file, this statement has become somewhat ambiguous, as _defaults does not (literally) apply to all services defined in the file. When setting autowire, it does only apply to the current services, not to the ones defined under the services if when is used in the same file.

Working example:

services.yaml

services:
  # default configuration for services in *this* file; (this is the default comment from framework bundle recipe)
  _defaults:
    autowire: true
    autoconfigure: true 

  App\My\Service: # has arbitrary amount of arguments

when@prod:
  services:
    _defaults:
      autowire: true
      autoconfigure: true 

    App\My\Service: # autowired arguments passed to service; works

Non-working example:

services.yaml

services:
  # default configuration for services in *this* file ; (this is the default comment from framework bundle recipe)
  _defaults:
    autowire: true
    autoconfigure: true 

  App\My\Service: # has arbitrary amount of arguments

when@prod:
  services:
    App\My\Service: # no explicit arguments given thus failing with "ArgumentCountError" as not autowired

The wording ...that it applies to all services defined in that file or # default configuration for services in *this* file (in the services.yaml) makes it seems as if the "Non-working example" should have worked as everything is defined in the same file (but it doesn't).

Suggestion

Add a note/warning to the autoconfigure option section that the _defaults need to be explicitely redefined when using when in the same services.yaml.