- Add abstract base class for Processing widget wrappers to c++
- Add wrapper factory interface to c++
- Make QgsProcessingGuiRegistry also register widget wrapper
factories, and be responsible for creation of new c++
processing widget wrapper instances
- Start on private c++ implementation of boolean widget wrapper,
including unit tests
Since these expressions were only evaluated immediately, it led to
confusing behavior for users who were expecting that the expression
would be applied per-feature.
Given that expressions can be directly entered into spin boxes, we already
have a way of users evaluating simple calculations for numeric
parameters at least.
I don't think there's a strong enough use case for needing to
calculate string results to leave the confusing expression builder
option in place.
This should be re-evaluated when we add UI support for dynamic
parameters (which are already supported in the backend), where
expressions are evaluated per-feature.
Fixes#17267
