Documentation: Add dynamic choice generation and checking examples to mkdocs.

[wolfiex]

Actual Situation

The ability to dynamically create choices is really useful and it should be given as an example in the documentation.

my_collection:
    type: str
    help: A collection of items
    choices: |
        {%- for my_item in items %}
        - {{my_item}}
        {%- endfor %}

And executed with

run_copy(copier_loc, out_dir, data = { "items": ['a','b','c'] } )

I am happy to add it to the mkdocs markdown, but am unsure where it would best live. Just following the Jinja/Macro templates subheading possibly? https://copier.readthedocs.io/en/stable/configuring/#importing-jinja-templates-and-macros

Desired Situation

More people are aware of the functionality.

Proposed solution

I add this to the documentation and it gets merged?

[wolfiex]

I would propose a similar solution to passing through a function and performing a conditional check:

iac:
    type: str
    help: Which IaC tool do you use?
    choices:
        Terraform: tf
        Cloud Formation:
            value: cf
            validator: "{% if not check_installed(cloud) %}Requires AWS{% endif %}"

And run as:

def check_installed(x):
    ...

run_copy(copier_loc, out_dir, data = { "check_installed":check_installed } )

[sisp]

Do you have an example where the choice items are not provided as runtime data? Or can you elaborate on your use case?

[wolfiex]

Both methods work fine. It would be nice to have an example in the documentation demonstrating their use.

A use case would be polling an API to establish the latest selection of available choices, or having a function evaluate the possible choices based on a non-arbitary selection of items (e.g. currently running processes)