Add logic for the new registration (static) variables

[Viicos]

After a lot of thinking about the technical implementation:

• Having all registration static variables registered under the same registry is not reliable, as I expect registration plugins to provide similar (if not identical) static variables, and duplicate identifiers would fail.
• To overcome this issue, each plugin can provide their own registry.
• get_static_variables was adapted so that it can iterate over a provided registry, instead of the default one for vanilla static variables.
• A bit unrelated but can be reviewed in separate commits: an endpoint returning the available registration variables was added. It is designed mainly as a backend for frontend endpoint.

This preserves backward compatibility, as get_static_variables([, submission=...]) will still use the default registry. It also works well this way because get_static_variables is currently used in:

• jsonlogic trigger validation: ✅
  

  open-forms/src/openforms/forms/api/validators.py

  Lines 126 to 128 in bed8118

  	# Check if the trigger references a static variable
  	needle_bits = needle.split(".")
  	for variable in get_static_variables():

  
  registration static variables shouldn't be referenced.
• Validate form variables are unique: ⚠️
  

  open-forms/src/openforms/forms/api/serializers/form_variable.py

  Lines 54 to 55 in bed8118

  	if item["key"] in static_data_keys:
  	errors[f"{index}.key"].append(

  
  Ideally registration variables should be taken into account as well. Not sure how common a name collision between a form variable and a registration variable would be. If we want to validate this, it might get tricky as every registration backend should be taken into account. So perhaps a new include_registration boolean option to get_static_variables could be added? (Issue is it is conflicting with the variables_registry argument).
• get_variables_for_context: ✅
  

  open-forms/src/openforms/variables/utils.py

  Lines 52 to 56 in bed8118

  	formio_data = FormioData(
  	**{
  	variable.key: variable.initial_value
  	for variable in get_static_variables(submission=submission)
  	},

  
  get_variables_for_context is only used for the Objects API (where it makes sense to not include reg. variables, those are added manually in the context by accessing ObjectsAPIRegistrationData) and the email backend (not sure about this one, probably doesn't make sense to have registration variables for this plugin anyway?).
• static variables endpoint: ✅
  

  open-forms/src/openforms/variables/api/views.py

  Lines 24 to 30 in bed8118

  	class StaticFormVariablesView(ListMixin, APIView):
  	authentication_classes = (authentication.SessionAuthentication,)
  	permission_classes = (permissions.IsAdminUser,)
  	serializer_class = FormVariableSerializer
  	def get_objects(self):
  	return get_static_variables()

  
  As expected, reg. variables are in a separate endpoint.

---

For tests, I'm planning on testing I tested the ObjectsAPIRegistrationData creation, in particular how it behaves when I get an API error when trying to create documents. Not sure where to put these, ideally I don't want to touch the big 1k lines ObjectsAPIBackendTests test class, although it might require some refactor?

Added registration variables will be tested in #3982, when the v2 registration will be tested.

[codecov]

Codecov Report

Attention: Patch coverage is 86.41975% with 22 lines in your changes are missing coverage. Please review.

Project coverage is 96.02%. Comparing base (bed8118) to head (86401a6).
Report is 28 commits behind head on master.

Files	Patch %	Lines
...ions/contrib/objects_api/registration_variables.py	68.96%	18 Missing ⚠️
...ons/contrib/objects_api/submission_registration.py	96.22%	0 Missing and 2 partials ⚠️
src/openforms/registrations/base.py	75.00%	1 Missing ⚠️
...nforms/registrations/contrib/objects_api/plugin.py	87.50%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3984      +/-   ##
==========================================
- Coverage   96.11%   96.02%   -0.10%     
==========================================
  Files         724      726       +2     
  Lines       22625    22753     +128     
  Branches     2607     2620      +13     
==========================================
+ Hits        21747    21848     +101     
- Misses        622      649      +27     
  Partials      256      256              

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[sergei-maertens]

I think this is too naive, you lose the information of which file/component the Document URL belongs too.

I'd still prefer to have the variable of a file upload explicitly mapped into the schema, e.g. something like:

type: object
properties:
  proofOfEmployment:
    type: string
    format: uri
  bankStatements:
    type: array
    items:
        type: string
        format: uri

so that you can make the (single) file upload "proof of employment" to /proofOfEmployment and the multi-file upload "bank statements" to /bankStatements

Possibly we do this in a separate PR

[Viicos]

Considering this requires thinking and probably some work, it will probably be part of the next PR

[sergei-maertens]

Just need to fix CI :)