[RFC][DX][Workflow] Configuration of initial places and marking store

[HeahDude]

Description

1. In [Workflow] Deprecate MultipleStateMarkingStore and SingleStateMarkingStore in favor of MethodMarkingStore #30551, the marking store has been "simplified" internally, but the configuration is now more confusing (ref [Workflow] Deprecate MultipleStateMarkingStore and SingleStateMarkingStore in favor of MethodMarkingStore #30551 (review)).

2. In [Workflow] Added support for many inital places #30468, initial_place has been renamed initial_places but still supports passing one place that will be normalized to an array despite this single example in the upgrade file. Also, this naming is now a bit confusing too, whether we can use it with one place is not obvious anymore.

Proposition

1. Simplify the method type configuration which is the only one built-in we want to support now, and infer the single state from the type of the workflow, this leaves one argument to configure, the property name:

   framework:
    workflows:
        article:
            type: state_machine # or workflow for multiple states
            marking_store:
                type: method # this line can be removed in Symfony 5.0
                property: state

   Instead of inferring we can use another key: state (single or multiple) along with property,
   or use a boolean as suggested by @pbowyer in the review linked above.

2. We could rename initial_places to something invariant like initial_marking or initial_state.

Any other suggestions? What do you think? ping @javiereguiluz @lyrixx

[pbowyer]

Re the marking store, this is how the 4.3 behaviour looks when added to the documentation: symfony/symfony-docs@6f51164.

I like the idea of inferring the single state from the workflow type state_machine. If there are complications, would it be bad though to keep single_state and multiple_state as wrapper classes/shims for easier configuration by developers? This doesn't change the implementation, but makes it obvious what developers need to use.

[HeahDude]

Currently I see a DX problem that should be handled at configuration level, because having state_machine by default (https://github.com/symfony/symfony/blob/master/src/Symfony/Bundle/FrameworkBundle/DependencyInjection/Configuration.php#L269) is not compatible with default false in the marking store (https://github.com/symfony/symfony/blob/master/src/Symfony/Component/Workflow/MarkingStore/MethodMarkingStore.php#L40).

[lyrixx]

@HeahDude Very nice idea. I love it. Would you mind submitting a PR?

type: method # this line can be removed in Symfony 5.0
This is not possible, since it could be a service (but could be the default value though)

[HeahDude]

Ok I can do it, thank you for the feedback.