Conditional adding/removing of choices

[MaciejPatro]

Hello

What is the intended way to handle adding/removing choices based on previously answered prompt?

The example is I want to let user have more options of unit testing frameworks based on C++ standard the project is supposed to support:

I've solved this problem in this way:

cpp_standard:
  type: int
  default: 17
  choices:
    Cpp23: 23
    Cpp20: 20
    Cpp17: 17
    Cpp14: 14
    Cpp11: 11
    Cpp98: 0
    
unit_testing_98:
  type: str
  default: null
  when: "{{ cpp_standard == 0 }}"
  choices:
    - GTest
    - None

unit_testing_11:
  type: str
  default: null
  when: "{{ cpp_standard > 0 }}"
  choices:
    - doctest
    - GTest
    - None

and using context hook I populate unit_testing with the correct choice.

Is there a smarter way of handling "conditional" choices? Because if I would like to introduce support for C++17 or newer unit testing framework I would need to again add another parameter and complicate the copier.yaml file even more.

[yajo]

There's really not a much better option available right now 🤔

This is the 1st time I see this use case.

I guess #698 will help you here, being able to validate an answer and provide feedback on why it cannot be chosen.

Also we could add support for the disabled property of Choice.

[MaciejPatro]

Thank you for quick answer!

I would guess for now I will keep the solution I came up with.

The goal for me was to ensure that users can't make a wrong choice in the first place.
Failing to generate a template for choosing an option that was given to the user seems as bad design of this particular template - for that reason I think validation is not really a good use-case here.

The disabled property seems interesting as this not only "saves" user from failing - but also allows to inform them what kind of configuration they need, to use the disabled choice (if for any reason they want it).

Maybe I will look in the weekend if the implementation is not too complicated.

[pawamoy]

Maybe we could remove empty choices from the list?

unit_testing:
  type: str
  default: null
  choices:
    - "{% if cpp_standard > 0 %}doctest{% endif %}"
    - GTest
    - None

Just like we don't create files/dirs with empty names?

[yajo]

I don't think this is a good idea. If you want a value that can be evaluated as false and your type is str, then "" is that value. My guess is that somebody out there can be already using that behavior.

I think it's better to support a more complex choice structure with extra keys such as disabled or when.