feat: questionnaire validation

[RoyalTS]

I'd love a possibility to validate questionnaire inputs. Being able to validate str against regex would already be a huge help, e.g. by specifying a field appropriately in copier.yml:

project_name:
  type: str
  help: Your project name
  validate: ^[a-zA-Z][_a-zA-Z0-9]+$

[yajo]

This was the feature I was hoping nobody asked 🤣

Yes, gotta do it.

However, I'm more o the side of allowing a Jinja template to validate, so you can validate any data type. It'd be interesting for YAML questions for example.

[eyllanesc]

my 2 cents: I think "validate" should accept jinja filters, and there should be filters like regex ones, range validators, etc.

[andrew-glenn]

@yajo Just to clarify - you're thinking an inline jinja template, versus a path to a jinja template on the local filesystem, correct?

FWIW my team is discussing this and considering a contribution; Just want to align with maintainer desires to (hopefully) fast-track any PR that we submit. :)

[yajo]

I was thinking on an in-line template that, if renders to an empty (or whitespace-only) string means OK, but if it renders to some text, that text is considered the error message. Does that make sense for you?

[pawamoy]

@yajo, could you provide some examples of Jinja templates as validators? I'm imagining single conditions for simple values, and multiline templates for more complex ones?

project_name:
  type: str
  help: Your project name
  validator: "{% if not project_name %}project_name cannot be empty{% endif %}"

metadata:
  type: yaml
  help: Your project metadata
  validator: |
    {% if metadata is not mapping %}metadata must be a mapping, not a list or other type{% endif %}
    {% for name, value in metadata.items() %}
      {% if value is mapping %}{{ name }}: value cannot be a mapping, only simple types or lists{% endif %}
    {% endfor %}

[yajo]

Correct!

Another example:

your_age:
  type: int
  validator: "{% if your_age <= 0 %}Must be positive{% endif %}"

[barrywhart]

@yajo: This feature looks really useful! If I understand correctly, it hasn't been released yet. Will there be a new release soon? 🙏

[yajo]

I wanted to release sonner, but saw there's some incompatibility with dependencies that you can see in #785. I want to at least fix that before the next release, or I'll get a flood of issues.

I still didn't have time though... if someone volunteers, the next release will be sooner.

[barrywhart]

Thanks! I may be able to look at it early next week.

Great project, BTW. We are switching from cookiecutter soon. 🙌🏽

[pawamoy]

I can take a look this week as well.

[barrywhart]

@yajo, @pawamoy: I have a possible fix for the test failures in #785. See PR #804.

[nils-borrmann-y42]

@yajo I'm a bit confused about this feature. This doesn't seem to be able to solve the original usecase of validating a regex. Obviously the validator could look something like this - but this fails since re is not available:

  validator: "{% if not re.fullmatch('[a-z-]+', project_name) %}invalid project name{% endif %}"

I tried a few things, but wasn't able to import re from the jinja template. A quick google search told me that it actually isn't possible to import modules from within a jinja template. What am I missing? How can I do a regex validation?

[pawamoy]

Either Copier itself could add some modules from the standard library into the Jinja context, or we could write an extension that does just that. The extension package would expose multiple extensions, one for each stdlib module of interest, and one that adds all modules of interest at once maybe? 🤔

[yajo]

Copier includes https://gitlab.com/dreamer-labs/libraries/jinja2-ansible-filters, which contain regex filters.

[nils-borrmann-y42]

Thanks, but I tried a few things and couldn't get this to work. Could you please give an example of what a regex validation could look like? (I guess this should also be added to the docs, considering that regex is likely one of the most common usecases for validations.)

[yajo]

Please would you mind to use the forum for this kind of questions? That'll be most helpful for the community, as there might be multiple ways of validating and some users would like to share them. Thanks for your understanding 😀