Clearify shorten configuration syntax

[wouterj]

The shorten syntax for connections and entity_managers in the configuration is truly great. But the current implementation has a very big flawback: The error messages are not clear enough. If you are not aware that there is a shorten version, you'll have a hard time understanding code examples in documentations.

We've had a couple of issues about this in the Symfony docs lately: symfony/symfony-docs#3878, symfony/symfony-docs#3946, symfony/symfony-docs#393

Assume you have this config (which is incorrect since it uses both the expanded and shorten syntax):

doctrine:
  orm:
    auto_mapping: true
    entity_managers:
      default:
        dql: ...

You get this error message:

Unrecognized options "auto_mapping" under "doctrine.orm"

As if the auto_mapping option doesn't exists at all.

I propose to improve these error message to include that you already use the expanded version and thus it needs to be placed under the specific entity manager. For instance:

The configuration contains specific entity managers, you should move the "auto_mapping" option to a specific entity manager.

/cc @weaverryan

[stof]

The error messages are coming from the Config component. They cannot be customized

[wouterj]

We can add some custom validation and use ->invalid to override the Config component messages, can't we?

[wouterj]

symfony/symfony-docs#4334

[wouterj]

We can now also add information to the error messages using the info option.

[alcaeus]

Closing here as this can't be changed since it's the config component handling things (and because the issue hasn't been touched in more than 4 years).