Improved customization for ConfigurableOperationDef (Promotions, ShippingMethods, etc)

[michaelbromley]

Is your feature request related to a problem? Please describe.
We have widely-used class, ConfigurableOperationDef, which is used as the basis of several runtime-configurable objects:

• CollectionFilter
• PaymentMethodHandler
• PromotionAction
• PromotionCondition
• ShippingEligibilityCheker
• ShippingCalculator

The definition allows the developer to define args which can then be configured at run-time with concrete values by the Administrator. In the Admin UI we generate form fields for this purpose.

The problem is that with the current implementation there are a number of limitations:

• The supported data types for the args are fixed and cannot be extended in any way. Supported data types are: 'string' | 'int' | 'float' | 'boolean' | 'datetime' | 'facetValueIds'. Note that facetValueIds is a kind of special case which is actually just an array of strings.
• The Admin UI cannot be customized to use custom components as input for these args values.
• Only simple data types are supported, there is no support for relations. E.g. the facetValueIds seems like it is a relation, but it is really just a dumb list of strings. True relations would be prefereable, and should be generic so that any entity can be related.
• List values are not supported.

Describe the solution you'd like
Disregarding the feasibility for now, here is the ideal solution:

• Args can be defined as any of the datatypes supported by custom fields, as well as a relation to any available Entity
• Arrays of any of those types are also supported
• There is a way to specify a UI component to act as the input control of that arg, in a similar way that we do with custom fields already.

Any breakthroughs in this area may also be applicable to custom fields, such as the ability to define lists and relations.

I have no design for this yet - this is quite a complex problem and after some exploration I'll add any implementation ideas I come up with.